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Home > Electronic Reading Room > Document Collections > Commission Documents > Commission Meetings, Slides, Transcripts, Meeting SRMs, and Full Written Explanation for Closed Meetings > 1997
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05/07/1997
1
UNITED STATES OF AMERICA
NUCLEAR REGULATORY COMMISSION
***
BRIEFING ON IPE INSIGHT REPORT
***
PUBLIC MEETING
***
Nuclear Regulatory Commission
Room 1F-16
One White Flint North
11555 Rockville Pike
Rockville, Maryland
Wednesday, May 7, 1997
The Commission met in open session, pursuant to
notice, at 2:01 p.m., the Honorable SHIRLEY A. JACKSON,
Chairman of the Commission, presiding.
COMMISSIONERS PRESENT:
SHIRLEY A. JACKSON, Chairman of the Commission
KENNETH C. ROGERS, Member of the Commission
GRETA J. DICUS, Member of the Commission
NILS J. DIAZ, Member of the Commission
EDWARD McGAFFIGAN, JR., Member of the Commission
. 2
STAFF AND PRESENTERS SEATED AT THE COMMISSION TABLE:
JOHN C. HOYLE, Secretary
KAREN D. CYR, General Counsel
JOSEPH CALLAN, EDO
GARY HOLAHAN, Director, Division of Systems Safety
and Analysis, NRR
WAYNE HODGES, Director of Systems Technology, RES
ASHOK THADANI, Deputy Director, RES
MARY DROUIN, IPE/IPEEE Section Leader, RES
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P R O C E E D I N G S
[2:01 p.m.]
CHAIRMAN JACKSON: Good afternoon. It is always
good to see the handsome faces. I am pleased to welcome
members of the Staff to brief the Commission on the IPE
insight report.
In November of 1988 the Commission issued the
Generic Letter 8820, requiring each utility licensed to
operate nuclear power plants to perform an Individual Plant
Examination, or IPE, of each of its plants to search for
previously unidentified vulnerabilities to severe accidents.
As a result of performing an IPE a licensee was
expected to develop an appreciation of severe accident
behavior, to gain an understanding of the most likely
accident sequences that could occur at its plants and to
gain a more quantitative understanding of overall
probabilities of core damage and fission product releases.
The Staff examined the IPE submittals to determine
what the collective IPE results imply about the safety of
U.S. nuclear power plants and how the IPE program has
affected reactor safety.
During today's briefing the Staff will summarize
the results of the IPE insights program examination. I and
my fellow Commissioners are looking forward to your briefing
today and I understand that copies of the viewgraphs are
. 4
available at the entrances to this room.
Good afternoon. Please, Mr. Callan, proceed.
MR. CALLAN: Good afternoon. With me at the table
are Ashok Thadani, the Deputy Office Director of the Office
of Research -- you are into your second week?
MR. THADANI: Second week, yes.
MR. CALLAN: I still want to say NRR.
Mr. Gary Holahan, the Director of the Division of
System Safety and Analysis from NRR; Wayne Hodges, the
Director of the Division of Systems Technology and Research;
and Mary Drouin, the Acting Branch Chief of the
Probabilistic Risk Analysis Branch in Research -- she works
for Wayne Hodges. She is also the technical lead for the
IPE program.
Mr. Thadani will give an overview of the IPE
program. He will then be followed by Mary Druin, who will
cover the status of the IPE program, the insights documented
in NUREG-1560, and the recent NRC IPE public workshop that
was held in Austin, Texas a few weeks ago.
Finally, Mr. Holahan will brief the Commission
about the NRC follow-up activities.
Ashok?
MR. THADANI: Could we go to viewgraph number 3,
please?
As you well know, following the accident at Three
. 5
Mile Island was tremendous activity, both within the
industry as well as at the Agency. Focus was starting to be
given to the potential for severe accidents that now became
more credible than they had been considered in the past.
During the early period after the accident, a
significant number of backfits were imposed on the industry
and a number of research activities were initiated, both in
this country as well as other countries.
In mid-1980s the Commission issued a policy
statement on severe accidents. In that policy statement the
Commission concluded that the existing plants do not pose an
undue level of risk to the public and that no immediate
changes were necessary. This statement recognized a number
of changes that had been imposed during the previous few
years as a result of the accident at TMI.
The Commission, however, recognized that there may
be some aspects of designs and that some plants may be
outliers in terms of potential impact on public health and
safety, and so the Commission indicated that the Agency was
going to move towards developing a systematic approach to
trying to understand what the impact might be on a plant-
specific basis.
As part of the severe accident closure plan, the
Staff had three key elements to address to ensure that the
issues of severe accidents were being adequately addressed.
. 6
The three elements were -- the first one was the
concept of making sure that there was much better
understanding of capability of containments, various types
of containments to deal with severe accidents.
There was a considerable margin in terms of design
of these containments and it was judged that the
containments could handle significant types of challenges
from severe accidents.
This was called the Containment Performance
Initiative. By and large it was the Agency's effort with
some limited work also done by the industry.
The second element of the closure plan was
accident management.
It was indeed critical to fully understand severe
accident behavior and a lot of research went into getting
that understanding.
With that understanding and the sense of
containment capability, it was then deemed that one can use
that information in conjunction with individual plant
examinations -- that is, a plant by plant look at the design
aspects that integrate this information and then make
decisions on whether any further actions were required,
backfits or whatever those actions might be.
The important element of this was the recognition
that IPEs provide very valuable information to the
. 7
licensees, that they can develop their command and control
activities in dealing with accidents, taking information
from Individual Plant Examination, the severe accident
behavior studies, and integrating them and making sure that
the emergency response organization then could deal, if
there were an accident deal with that accident.
These were the three key elements. Of course,
today we are going to be discussing what was in Generic
Letter 8820, and as the Chairman noted, the objective there
was to look for potential vulnerabilities on a plant-
specific basis.
CHAIRMAN JACKSON: Let me ask you a question
before you go on. How many generic issues are there that
are on the books? How successful have we been in resolving
them, using IPE insights or results?
MR. THADANI: I don't know the number of generic
issues we have on the books, but a fair number of generic
issues have been resolved on the basis of getting some
insights from these Individual Plant Examinations.
One that clearly comes to mind is one of the more
important ones, which was reactor coolant pump seal LOCA
issue, and the Commission indicated that the Staff should
follow up on the basis of looking at the Individual Plant
Examinations -- but we can get the numbers.
CHAIRMAN JACKSON: I think it would be useful
. 8
because I think it seems that we have some softness in terms
of how many generic issues are still out there, and the
question would be is there a systematic approach to
resolving or dispositioning them?
MR. THADANI: There are two elements that I may
just touch. Clearly, the first -- whenever there is a
generic issue identified there is clearly prioritization
that is done and the prioritization utilizes information
from the Individual Plant Examinations and then in some
cases even resolution is based -- but we will get the
numbers.
CHAIRMAN JACKSON: Well, it relates really to two
things. It's systematic disposition of the generic issues,
and the second is the use of the IPE.
MR. HOLAHAN: There is an additional set of
generic issues associated with the IPEEE program.
CHAIRMAN JACKSON: Right.
MR. HOLAHAN: That have to do with external
events, and of course the Agency has a tracking system
for --
CHAIRMAN JACKSON: I know, but the issue has to do
with resolving them as opposed to tracking them.
MR. HOLAHAN: Yes, but there are many of them I
think which -- for which IPE is not the ideal mechanism for
resolving those issues.
. 9
CHAIRMAN JACKSON: I think Commissioner Diaz --
COMMISSIONER DIAZ: I was just going to say that
if we are going to get the numbers, they might be in some
categories so that we can determine this and work on it.
CHAIRMAN JACKSON: That is the whole point of
using the IPE results, because they give you a way of
assessing risk significance to the extent that they are
useful.
MR. HOLAHAN: Yes.
MS. DROUIN: What I would also add is that as part
of the generic letter the licensee could elect to try and
resolve on a plant-specific basis a generic issue, and there
were some that some of the licensees for the most part most
licensees did not elect to resolve generic issues.
There were some. We do discuss that in the NUREG.
CHAIRMAN JACKSON: They elected not to do it on a
plant-specific basis?
MS. DROUIN: On a plant-specific basis.
CHAIRMAN JACKSON: But what about invoking IPE
results to -- as part of those plant-specific --
MS. DROUIN: That is what I am saying. Very few
of them did.
We are going to be issuing a report over the next
couple of months in terms of what generic issues were
resolved through the IPE process.
. 10
CHAIRMAN JACKSON: That would be helpful. Yes,
okay.
MR. THADANI: Yes, I think that would address the
question you have raised.
May I have the next viewgraph, please -- no,
Viewgraph Number 4, please.
Again, you have covered, in your introduction you
covered the focus in attention of the generic letter. I do
want to make a point that the probabilistic risk assessments
are probably the only tool we know where you integrate
design and operational aspects and you take a total look at
the plant rather than a part of the plant at a time, so to
speak.
In that sense, it provides very useful, very
important understanding of the behavior and interaction of
man-machine, so to speak.
And we in the generic letter emphasized the
importance in terms of participation on the part of the
utilities in the conduct of these studies, and a number of
licensees did play a fairly active role in the conduct of
these studies, and in fact when we go through some of the
results and so on, the maximum I would say the biggest
benefit of these studies was (a) the understanding on the
part of the industry, and as I said, it's being utilized as
part of accident management plan. But also during the
. 11
conduct of these studies, some licensees identified some
significant safety issues, and in some cases actually made
changes, design changes, before they in fact submitted the
individual plant evaluations. And I think that was -- in my
mind that was a great benefit, because these were
potentially very significant outliers they identified during
the conduct of the evaluations, took corrective actions, and
in many cases, the results they submitted took credit for
those modifications. So I want -- the point I want to make
is the purpose of the IPE in that sense was served initially
through these evaluations.
CHAIRMAN JACKSON: Well, in a sense, doesn't that
address the fourth objective?
MR. THADANI: Yes, but there are two parts to
that. The first one is what I would call very significant
safety problems that they identified and fixed essentially
by and large. The next step is are there still some
concerns, some potentially significant contributors? I
would put these in generally two categories. Some would be
very plant-unique. Maybe there is a significant accident
sequence. It's a very plant-unique issue. If we want to
take action of course we would use our backfoot requirements
rule to make sure we're consistent with our procedures.
Another element of this is when you see similar insights
from let's say 20, 30, 40 plants, and the one you've heard
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more than once I know, for example, station blackout is
still an important contributor when you look at these
studies, so there's that generic implication there still,
and as you will hear, our plans are to look at both
elements. Should we be taking plant-specific followup
actions? And we are reassessing some generic issues such as
station blackout. I mentioned that in an earlier --
CHAIRMAN JACKSON: You've identified a time line
on which you plan to do this?
MR. THADANI: Well, I received the message of the
schedule I had for station blackout which initially was
1298. We're relooking at that as I indicated during the
grid reliability discussion. We will be reassessing
schedule.
CHAIRMAN JACKSON: So would you say that there are
licensees or any licensees that did not meet the fourth
objective of reducing the probabilities, because -- where
there were significant contributors to risk?
MR. THADANI: There -- if I may hold back on that
one, if you focus only on IPE's, then I think by and large
licensees have taken what I would call at least minimum
steps. There may be other things that could be done. You
will hear a little bit about some plants. There are some
questions about how close they come to quantitative health
objectives. There may be other things that can be done, and
. 13
perhaps ought to be done. That's now our responsibility to
see. I will qualify my comments by saying that is only on
IPE's. IP triple E's there are already some indications, at
least I know of one plant where there's a significant issue
on fire. That licensee has made initial modifications to
reduce risk from fire, but there are still some questions
how far have they reduced risk from fire, and we're going to
be looking at that issue further.
COMMISSIONER ROGERS: Just before we leave this, I
may be wrong on this, but my recollection is that when we
got into the IPE process, when we first started to think
about requiring IPE's, it was really on the basis of closing
the severe-accident program, and that that looked like the
final cap of that program, to ask each licensee to do an
individual plant examination. Now, there was no requirement
that that be done using a PRA. As a matter of fact, back in
1988, as I recall, we were very antsy about using risk
analysis, PRA analysis, that when we're talking about
probabilities and risk and so on and so forth, it was with
some ambivalence about how to do this, and we certainly
didn't require that every plant do a PRA. They had to do a
plant examination, and they had flexibility in how they
could do it. In the long run it turned out I guess that
everybody did a PRA, when all things shook down.
MR. THADANI: Yes.
. 14
COMMISSIONER ROGERS: But I think that it is
important to keep that in mind, because the general approach
was, in my recollection, that this was really to be a value
to the licensees in understanding their plants better in
light of the severe accident possibilities, not for all
purposes in the plant, but really originally directed
towards closing the severe-accident program. And what I
think is happening here, and I'm not sure it's a bad thing,
but I think we ought to recognize that it's happening, that
we are drifting over now into using the results of the
IPE's, which now have turned out to be PRA-based, for
broader purposes. Now that may be very good, but I think
that one should recognize that we are taking steps beyond
what the original purpose of the IPE was, and I'm a bit
concerned because I feel that at the time that -- and I may
be not quite right on this, and the record will have to be
looked at to find out -- that I think the Commission's
general posture of the Commissioners was that we weren't --
we didn't expect to use those IPE's for regulatory purposes.
MR. THADANI: If I may comment on that, you're
quite correct. In the '88 time frame the focus clearly was
to identify those potentially handful of plants which may
pose significant risk, and so to identify what we called
outliers --
COMMISSIONER ROGERS: Right.
. 15
MR. THADANI: That was the language. And it's not
to say that the staff was -- I think the staff was of the
view that risk assessments -- doing risk assessments was a
good idea. The concern was the cost of risk assessments,
and staff had a dialogue with the industry, and there were
simpler methodologies developed by organizations outside
which we said -- which was short of risk assessments -- with
reduced scope as a matter of fact which we said would be
acceptable to meet the intent of these evaluations, but the
industry chose to go beyond, and they did spend more
resources, and that was the basic concern we had.
COMMISSIONER ROGERS: Well, I think our own
resources, I think we made a statement that we couldn't
possibly review every one of these --
MR. THADANI: That's absolutely correct. We could
not review these.
The staff review of the IPE's has always been
mindful of what was the intent of these studies, and the
scope of the reviews therefore has also been fairly limited
in that sense, but as we go into the kind of regime that
we're talking about now of risk-informed use in essentially
all of our regulatory activities, then the issue of scope,
quality reviews and so on clearly has to be --
COMMISSIONER ROGERS: Oh, absolutely.
MR. THADANI: Consistent with that application.
. 16
COMMISSIONER ROGERS: I just think that it's
important that the Commission keep in mind that historical
background, because we didn't start out with this program as
a uniform PRA for every plant, that then we would look to
see what more could be done on the basis of it. It was
really to really find the outliers.
MR. THADANI: Yes, indeed. That was the
objective. And now --
CHAIRMAN JACKSON: Well, were the IPE's
consistently reviewed or was there guidance to ensure
that --
MR. THADANI: We had guidance for consistent
review of the IPE's. The issue is the scope and the depth
of our reviews was fairly -- in most cases I guess we call
step 1, and then step 2 reviews. The scope and depth of
step 2 review was higher than that of step 1. We had to
have a reason to go on to step 2 review because of resource
considerations, and Mary can probably tell you if you're
interested that what level of effort we expended on these
reviews, it was not very significant, if you look at a
plant-by-plant basis.
CHAIRMAN JACKSON: You say it was not very --
MR. THADANI: Not very significant.
CHAIRMAN JACKSON: Okay.
MR. HOLOHAN: Could I add something before we
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leave the subject? That is, in trying to come to grips with
the issue of where did we start on the IPE program, and
where are we going in the future, I think it's helpful to
distinguish between what is IPE and what are PRA's. The IPE
was really intended to be a one-time examination of plants.
The PRA's are really the tools to do that. I think in the
long run the PRA's have a role, but the IPE's I think will
come to an end. I think there are some additional things
that we are talking about doing, and sometimes we get a
little confused about the IPE's as though they are the
tools, and I think it's helpful to maintain that distinction
between the tool and the program, and the IPE reviews were
for the purpose of the IPE program. Were the analyses good
enough to find vulnerabilities? Now when we're talking, as
we did yesterday, talk about future uses of PRA, I think it
raises, you know, additional issues and additional reviews.
CHAIRMAN JACKSON: So the PRA's were a tool to do
the IPE's.
MR. HOLOHAN: Yes, exactly.
CHAIRMAN JACKSON: It was of finite duration.
MR. HOLOHAN: Yes, exactly.
CHAIRMAN JACKSON: Always meant to be with a
specific focus, but the PRA's live on with these other
regulatory potential uses?
MR. HOLOHAN: Exactly.
. 18
CHAIRMAN JACKSON: A la the discussion yesterday.
MR. HOLOHAN: Yes.
CHAIRMAN JACKSON: Okay.
MR. HOLOHAN: Or maybe even newer and better
versions of PRA for future uses.
CHAIRMAN JACKSON: Okay.
MR. THADANI: Okay. Mary.
MS. DROUIN: Okay. Slide number 5, please.
Before we get into NUREG 1560 I think we can
benefit by talking just briefly about the whole IPE program,
because the IPE program is much broader than the actual
NUREG that was issued. Two points here that I want to make
on the slide is one, in looking at all these IPE submittals,
the staff received a tremendous amount of information on
severe accidents, plant design and operating
characteristics, core damage frequency, system dependencies,
so when you look across these 76 submittals, the wealth of
information there was just tremendous.
In trying to understand all the information that
was contained in these submittals, we divided up the program
into four primary activities.
The first one, of course, was to look at each of
the submittals and review them against the intent of the
generic letter. Was the analysis, as Mr. Holahan said,
adequate enough such that had a vulnerability existed at the
. 19
plant and indeed been discovered.
In parallel with that, we created an IPE database
where we took information out of the submittals, entered it
into a database that allows the user to query across plants
so if you are interested in something on a group of plants,
you could get that without having to dig through 76
different volumes of information.
Also, as we were reviewing -- all these activities
have been going on in parallel. We have been going out to
each of the regions, meeting with the resident inspectors
and various regional personnel, providing them insights on a
plant-specific basis of what we have been learning from
these IPE submittals.
And then, lastly, the main topic for today is
NUREG 1560, what we have documented as the different
insights that we have gleaned from looking at all these
different submittals.
COMMISSIONER ROGERS: Just before you leave that,
how do you define within class in the IPE?
MS. DROUIN: Within a class, we define class, for
example, when you are looking at the reactor design by
interpolis design so we are looking at the BWR 1/2/3s, the
isolation condenser plants, the BWR 3/4s, Westinghouse four
loops, Combustion Engineering BMW and then on the
containment side, dividing it by containment type and that
. 20
is what we meant by class of plants.
Just quickly, also giving you a status of where we
are on the four various activities, in terms of the IPE
reviews, out of all of these the staff evaluation reports
have been issued to NRR and to the licensees on all the
submittals except five and we are in the midst of wrapping
up these remaining five as we speak.
In terms of the IPE database, it's complete. It
has been made available to the public. It is on the web
page and we have also issued a NUREG. I believe it is 1603,
which is a user manual of how to use the database.
COMMISSIONER ROGERS: Do we have any information
on users of that database, yet? I mean, do we have any
indication of how useful it is or has been so far?
MS. DROUIN: Well, we have been using it
internally for several years now.
COMMISSIONER ROGERS: I was thinking, since it's
on the Internet.
MS. DROUIN: In terms of the public, we just put
it there. I mean, it's been there like less than two weeks.
So in terms of how many people have downloaded it --
COMMISSIONER ROGERS: I had a little trouble
getting on it myself this morning.
MS. DROUIN: Well, we will be delighted to come up
and personally, you know, load it for you.
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CHAIRMAN JACKSON: What use have the regions made
of the IPE results?
MS. DROUIN: I think a lot in their inspection
activities because we have also been given briefing for the
inspections, the IPAP inspections, day to day decisions.
MR. CALLAN: Chairman, Mary is right. The regions
are getting into it but they have been lagging NRR
substantially and it has only been in the last several
months that the graduates from this two-year training
program, the -- what's the title?
MR. THADANI: Senior reactor analyst.
MR. CALLAN: Senior reactor analyst, which is a
fairly intense qualification process, are now starting to
become productive and that was a major, major step in the
process of exporting PRA expertise to the regions.
Now speaking as an ex-regional person is one of
the frustrations the regions have is their perceived
inability to interact with the licensees in their region on
PRA issues and licensees, as you know, are making increasing
use of PRA risk insights and all facets of their
interactions with the staff, whether it be on enforcement
issues, requests for enforcement discretion and the whole
range of issues that we interact and the regions are very
frustrated because they don't have the expertise to deal
with those things without extensive support from NRR.
. 22
CHAIRMAN JACKSON: So it is an expertise issue,
not having put the framework into place?
MR. CALLAN: Yes. The inspection procedures are
out there, the training programs are in place but the
regions don't have the expertise, the sophistication.
CHAIRMAN JACKSON: In the regions?
MR. CALLAN: In the regions at this point.
As I said, that may change in the coming year or
so as the SRAs, the senior reactor analysts, start stepping
out and exerting some leadership.
CHAIRMAN JACKSON: Do we have -- I mean, are we
going to have going out this year senior reactor analysts to
each of the regions at least?
MR. CALLAN: Each region has two billets. One of
the problems is that the individuals who were selected for
these positions were, as you would expect, are among the
best and brightest of the inspectors. They are also the top
candidates for promotion and several of them have been
promoted. Several of them are now in headquarters. Some
have been on your staff and my staff and because -- so there
has been a substantial turnover in the role. That was
intended, actually.
The intention was to train these people and have
them move on but, unfortunately, the demands of the
organizations have often plucked them out of the training
. 23
program prematurely so that has been frustrating.
This will take time to get the regions up to
speed. The regions are definitely lagging in this area.
CHAIRMAN JACKSON: That's interesting. Okay,
thank you.
MS. DROUIN: Okay.
Regarding NUREG 1560, we did publish volumes one
and two last October for public comment. Over the last
several months, we have received comments from a dozen
utilities. We have received comments from EPRI, from NEI
and other members of the public. We held a three-day
workshop back in April and we had an attendance of about 100
people and I am going to speak more to the workshop later on
in the presentation.
We do plan on issuing a final version of the NUREG
this summer.
Okay, NUREG 1560. As I spoke earlier, when you
look at all these submittals, there is just a tremendous
amount of information and deciding what perspectives, what
insights, how you are going to slice information was a job
in and of itself. What we finally settled on was to look at
it from four different perspectives. One was first going
back to the original intent of the generic letter which was
the impact on reactor safety. So that was one of the first
objectives in terms of the perspectives we wanted to get
. 24
from these submittals and document.
The second one was now looking more towards the
actual results in the submittals, you know, looking at the
core damage frequencies at the accident sequences, at the
containment failure modes. What were the results telling us
in terms of reactor design and containment performance
versus the assumptions that are in these analyses? So we
were trying to get perspectives on that item.
Third, moving away from the actual results,
looking at the models and the methods that were used, what
insights and perspectives could we learn about the models
and methods that were used in these submittals and to
provide perspectives on that one.
Then, last, there were two things that we were
explicitly asked to look at. Was one, what could we say
from the IPE results regarding the Commission's safety goals
and also what has been the impact of the station blackout
rule and core damage frequency. So we were looking at the
results for that too.
Next slide, please.
Before I get into some of the results, I think it
behooves to put into perspective, into context, what NUREG
1560 addresses and what it doesn't address. First of all,
it was 75 submittals we looked at that covered 108 units so
we did make the decision early on that the perspectives were
. 25
going to be treated on a unit basis, not a submittal basis.
That seems trivial but that actually can really skew your
results and your insights but we did decide --
CHAIRMAN JACKSON: I was actually going to ask you
a question about that when you said there were 75 and I knew
there were more units than it actually represented.
MS. DROUIN: Yes. It represents 108, so we did
treat the results on a unit basis.
Also, the IPEs only cover a level one two PRA at
full power internal events only with internal flooding. So
perspectives regarding low-power shutdown, other modes of
operation, external events, those are not covered in this
insights report.
Now, some of the external events stuff will be
covered later on as part of the IPEEE program but it is not
in this document.
Next is that we do recognize that these PRAs were
originally done back in the era of about 1990. Utilities
have been, in some cases, updating them. That updated
information is not reflected in here. It is based on the
original IPE submittals.
And, lastly, the accuracy of the information is
not reflected so if a utility told us they had a two-train
system, we believed them so we did not go and verify --
CHAIRMAN JACKSON: So you didn't verify any of the
. 26
IPE results for any of the plants by, say, getting the fault
trees and event trees and looking at it in terms of the
systems for any of the plants?
MS. DROUIN: No, that's correct.
CHAIRMAN JACKSON: You just took it as it was?
MS. DROUIN: We took it as it was.
COMMISSIONER ROGERS: What would be -- how
difficult would it be to update, you know, the third bullet?
The fact that, you know, you took things -- this report --
MS. DROUIN: Can I address that later on? Because
that is something we will talk about when I get to the
workshops, what we plan to do.
COMMISSIONER ROGERS: Oh, sure.
MS. DROUIN: Next slide, please.
Okay, if we look at the first objective, which was
the impact of the IPE program on reactor safety, there were
several questions that we asked ourselves in pursuing these
perspectives and, you know, what was the type of
vulnerabilities that were identified, you know, what were
the improvements and what was the impact of these
improvements on the overall safety.
And what we saw was, first, that very few
vulnerabilities were identified. That was more, I believe,
due to the different definition that was used for
vulnerability. Vulnerability was not defined in the generic
. 27
letter or NUREG 1335, which was the supporting guidance
document. Definition of vulnerability was left to the
licensees and we saw many different definitions. Most of
them came down to either using, for example, like one E
minus four per reactor year and if you were above that, it
was the vulnerability. If your accident sequence or
contributor, for example, was greater than 50 percent of
your core damage or your containment failure, that would be
a vulnerability.
Some of them use sensitivity analyses but they
were different definitions.
CHAIRMAN JACKSON: So the industry did not develop
itself some overall --
MS. DROUIN: There was and it was the NUMARC but
not every licensee, only about 25 percent of the licensees
elected to use the NUMARC guide document for their
definition of vulnerability. I think it was around 25
percent.
CHAIRMAN JACKSON: Okay, Commissioner Dicus, I
think, had a question.
COMMISSIONER DICUS: Pretty well along those
lines, but I guess I want to be sure I understand this.
So few "vulnerabilities" were identified not
necessarily because there are few but because of the
definition issue? Is that another way to look at this?
. 28
MS. DROUIN: I think that is one way to look at
it, but I would think the next thing is to look at the next
bullet. Regardless of whether a licensee explicitly used
the word "vulnerability," they all identified weaknesses or
safety issues, if you want to call it that, and identified
improvements.
CHAIRMAN JACKSON: Do they credit the IPE program
for those improvements?
MS. DROUIN: Yes. Well, I don't want to say --
they discussed them in their submittal. So if you go to
each submittal, there are improvements that are discussed in
great length in each submittal that have been made. I would
suspect that probably some of them, if they weren't an exact
result of the IPE analysis, they certainly are using these
improvements.
CHAIRMAN JACKSON: Okay.
MR. THADANI: If I may, NUMARC issued guidance
document and in terms of their thought process on what
should one do with the results and they indicated they had
two key areas. One was frequency of core damage and the
other was frequency of potential for large early release.
In terms of frequency of core damage, they
indicated that if that frequency is greater than 10 to the
minus four, design options should be considered by the
licensee, design improvements hardware changes, whatever
. 29
have you. If the frequency of core damage is in the range
of 10 to the minus four to 10 to the minus five, one could
look into procedural improvements and enhancements. And if
the frequency was below 10 to the minus five, then that
could be considered down the road as part of accident
management considerations.
As far as frequency of large release is concerned,
everything I said applies except reduced by an order of
magnitude in frequency. Frequency of 10 to the minus five
for large releases, if it's higher than that it is either
design or hardware changes. Ten to the minus five to 10 to
the minus six, look at procedural changes. Below that,
then, look at it down the road as part of accident
management.
We -- we thought that was a fairly reasonable
approach and it turns out, I would say, reasonably
consistent with some of the things we have been talking
about.
COMMISSIONER ROGERS: When did we settle on our
definition of a large release? When -- what point --
MR. THADANI: We never did settle on the
definition of large early release. What we settled on was
we will convert that to early containment failure and we
defined early in terms of number of hours after onset of
core damage. But we didn't really end up defining large
. 30
early release because we started out with release that has a
potential for prompt fatality. One or more. And then there
were a lot of discussions back and forth.
So what we have now is, I might say, some kind of
surrogate means of saying if these conditions exist we
believe that would lead to a large early release, without
defining what that is.
COMMISSIONER ROGERS: I understand. But when did
we come to the conclusion of what that definition of what
that surrogate is?
MR. THADANI: In 1993, in a Commission paper, we
indicated the difficulties with the definition and the SRM,
I don't remember the dates, but soon after the SRM came
indicating, discontinue those studies of trying to define
large early release.
COMMISSIONER ROGERS: The only problem I was
trying to get at is when the licensees had something to work
with that was more or less common --
MR. THADANI: I think this -- their definition
was, I think, reasonably consistent. We used early
containment failure and they also were talking about early
containment failure. And the differences, I think, could be
in timing of early containment failure. But the thought
process still was, does it lead to early containment failure
and as you know, over the years we have had a number of
. 31
issues, what kind of challenges one should worry about with
the potential for early containment failure.
We have taken some actions in those areas, I
think, over the last several years and, by in large, it has
been a timing approach.
MR. HOLAHAN: The other thing I would add is
regulatory analysis guidelines contain effectively a
definition of -- a working definition of large early release
in the context that Mr. Thadani mentioned but also in the
guidance documents we spoke about yesterday.
The regulatory guides of standard review plans
provide effectively a working definition for large early
release. That's a little different, but basically what Mr.
Thadani said. It's a timing issue with respect to core
damage and containment failure.
MR. THADANI: The definition is in fact given in
the regulatory analysis guideline, and it talks about x
hours after onset of core damage as a definition.
CHAIRMAN JACKSON: Please?
MS. DROUIN: Okay. Just to give you a couple of
examples of some of the improvements, we certainly saw a lot
of improvements were associated with loss-of-power concerns,
and we are seeing improvements, you know, like adding,
replacing diesel generators, increasing redundant offsite
power capabilities, improving the ability to cross-tie from
. 32
buses or units. We saw things, replacing the emergency core
cooling system pump, air -- motors with air-cooled motors,
using the fire water system for core cooling. Also using
the fire water system for sealed cooling to your pumps,
increased training for feed-and-bleed operation. So this is
just a small sample of the improvements, but I think we
cataloged like over 500 improvements when you went through
across all the 70-some-odd submittals received by the staff.
Of all those improvements we did try and get a
feel for what was the status of them, and at the time of the
IPE submittals that we're now going back you know to the
1992 time frame, about 50 percent of those improvements had
been implemented at that time.
CHAIRMAN JACKSON: Let me ask you this question at
taking great risk, but if you look back at some of the
requirements that came post-TMI, are they any of them that
upon review or that the IPE insights would suggest were less
significant or less important than others? Or have you
really done that examination?
MR. THADANI: We haven't done that examination.
It may not be very easy to do that, but the converse I think
one can say that a number of the changes clearly were
significant improvements.
CHAIRMAN JACKSON: Okay.
MS. DROUIN: I would agree with that. I'm sorry,
. 33
I lost my train of thought.
One of the things is that we also did look at as
part of the review to see what level of participation, you
know, the licensees had in their analyses, and we did see
that there was a good-faith effort. I mean, we did not -- I
don't recall of an instance -- I mean, I could be wrong, but
I don't recall one -- where a licensee just went out and
turned over their IPE to a contractor. You saw a lot of the
work being performed in-house so that you were seeing, you
know, this in-house capability certainly increasing.
I don't want to mislead you, because one of the
things that did come out of the workshop, you know we're now
in the time frame of 1997 versus back in 1990 when they were
being done, but one of the things that did come out of the
workshop was even though this in-house capability had, you
know, increased, we're now starting to see a decrease,
because of a sense of frustration on the public, you know,
how quickly we're moving forward in this area.
Next slide, please.
If we move to the second objective, which was
looking at the results themselves and what they were telling
us, some of the things that we were trying to get a feel for
is that when you take a class of plants, for example, if you
look at all your BWR 6's or you look at all your CE plants
or you look at your large, dry containments, within that
. 34
group you see tremendous variabilities in the results, and
begs the question, you know, what's driving this
variability? Is it due to plant-specific design
differences, or is it due to assumptions or methods, you
know, how does the human play a role in this. And these
were the type of things that we were trying to derive as we
went through all of these submittals.
The biggest thing that comes out is that the
plant-specific features certainly play a tremendous role in
that variability, and I can't emphasize that enough. No two
plants look alike when you start getting into the depths of
these plants, and you start looking at the support systems,
you start looking at electric power, at service water, at
component cooling water, these plants start looking very
different, and these are the things that tend to drive the
results. But at the same time the differences in the scope
and the boundary conditions and the assumptions also played
an equal part in causing the variability. So it's not
strictly plant design, you have a mixture of these two in
there.
When you look at the results across the plants,
you do see that station blackout and transients are the
primary contributors to risk across all the plants, whether
you're looking at boilers or whether you're looking at your
pressurizers, and even when you look at your individual
. 35
classes. However, when you start looking at on a plant-
specific basis and trying to understand the reason, the
reason from plant to plant to plant varies. Why station
blackout is important at one plant and why it's important at
another plant are for very different reasons, and that
usually gets down into the design differences of the support
systems, and in many cases also of the analysis assumptions
that are behind it.
When we started looking at the human actions, this
was a little bit more difficult, because this is the one
area where you have very much inconsistency in how some of
the methods are applied, and I'm going to talk a little bit
more than that, but I think the biggest thing that we noted
is that what human actions are important is probably more
driven by analysis here than plant-specific design
differences. When you start looking at what were the top
human actions, it wasn't surprising what we saw. I mean,
for the boilers you saw depressurization, containment
venting, aligning containment or suppression pool cooling,
initiating your standby liquid control system, on the PWR
side of course the switchover to recirc where you don't have
the automatic switchover, feed and bleed, depressurization,
and cooldown, these were the ones that tended to be the top,
but they weren't important in every single plant.
CHAIRMAN JACKSON: Let me ask you this question.
. 36
This is more similar to Commissioner Rogers' question about
large early release. Is there a common definition of core
damage used in all of the --
MS. DROUIN: You preempted my next slide.
CHAIRMAN JACKSON: Oh, so sorry.
MS. DROUIN: So why don't we go to the next slide,
because I think that's where the heart of a lot of this is.
When we got past the results in trying to, you know, look
at, you know, the design differences and the assumption
differences in terms of, you know, what was causing the
variability in the results, you know, the other thing of
course that we were looking at, you know, was what -- and
where were the strengths in these models and methods, and
where were the weaknesses, and were the weaknesses more due
to a lack of knowledge versus misapplication of the method,
and I think that's a very, you know, difference between the
two, because in some cases it's not a lack of knowledge,
it's a lack of -- misapplication, and that's really what we
found.
When you looked at the different methods that are
used in these PRA's, when you look at your systems analysis,
your accident sequence analysis, your plant damage that your
containment of entry, the methods and the models behind
them, you know, are very well established. The problem
comes into how they implement these methods when you look at
. 37
the scopes and the boundary conditions, you start seeing
very differences, and I'll address, you know, for example,
the core-damage definition. There's not a standard core-
damage definition, so you could see anywhere from someone
defining core damage as once the reactor water level gets
below the top of active fuel to two feet above the bottom of
active fuel, to the peak cladding temperature. You saw a
varied differences, and there's no right or wrong in this
case, but it bounds and it scopes the problem, and they
will -- you will now get very different results.
CHAIRMAN JACKSON: Well, let me -- you know what
my next question inevitably is going to be, and that is, you
know, this is along the line of some of what we were
discussing in the briefing yesterday where we were talking
about, you know, five 10 to the minus 4 versus five point
one 10 to the minus 4. Since core damage frequency is what,
you know, many of these PRA's reference, what can you tell
me?
MS. DROUIN: I think it's like any analysis. You
have to look at what the analysis handles and what it
doesn't handle, and it doesn't mean the number is right or
wrong. I think when you look at any engine in the analysis
and you look at, you know, what was the input and what was
the scope that dictates then, you know, what that result
means.
. 38
CHAIRMAN JACKSON: No, I appreciate completely
what you're saying, but, you know, we have some triggers or
thresholds or whatever that are built into --
MR. HOLOHAN: Guidelines.
CHAIRMAN JACKSON: Guidelines. Okay.
MS. DROUIN: And if you get into the -- because I
was here yesterday, and if you start looking at the
uncertainties in the distribution on these things, if you go
back, for example, to NUREG 1150 and you start looking at
other PRA's and you look at what their distributions are,
and I'm just going to focus in on the level 1 part, because
that's all I have in my head at the moment, but if you look
at what their main values are, and you look at what the 95th
percentile, what you see is a factor of 3.
CHAIRMAN JACKSON: Okay.
MS. DROUIN: You do not see, you know, a factor of
10 or a factor of 100.
CHAIRMAN JACKSON: You don't see orders of
magnitude.
MS. DROUIN: No, you do not.
CHAIRMAN JACKSON: Okay. Then that's the most --
okay.
MR. THADANI: But I would also -- I think I would
also hasten to add that that's a rather stylized look at
hardware data.
. 39
CHAIRMAN JACKSON: Yes.
MS. DROUIN: Yes.
MR. THADANI: I think what we're talking about
could be more important, and if you step back and look, what
Mary said was dominant contributors are transients, which
means if you're starting to uncover the core, it is -- it
could take some time before one can get to a peak clad
temperature of 2,200 degrees Fahrenheit, which means there
is that much time available for intervention, corrective
action, and so on. That means that is a conservative
analysis if we accept peak clad temperature of 2,200 degrees
Fahrenheit as reflective of core damage. What that says is
that the licensees in some cases have made more conservative
assumptions on failure definition and that the results are
probably biased in that direction. Sometimes that is done
just to reduce the cost, because it is much simpler to go
forward with those assumptions, and this is just one
example. There are differences sometimes in success/failure
criteria. Some licensees will go to greater lengths to try
and better define what is that minimum required to deal with
a challenge. Others will not do that. They will use what is
a final safety analysis report, transient and accident
analysis values, which we know are conservative. So there
will be those differences.
CHAIRMAN JACKSON: Mr. Holahan, you had a comment?
. 40
MR. HOLAHAN: I just wanted to mention that what
Mary was talking about is the amount of variability that you
see in the analysis. That doesn't reflect those things that
you didn't analyze, which I think are also an important
contributor to the uncertainties, and it doesn't really
reflect also the fact that something in the analysis might
be an error or some sort of a bias. So I think although I
would think that a factor of three is maybe the minimum
value, I don't think we're talking about orders of
magnitude.
When I see the number 4.1 times ten to the minus
five, it means to me that the answer is somewhere between
ten to the minus four and ten to the minus five. It's in
that range.
CHAIRMAN JACKSON: Okay. Let me ask you this
question. How many of the inconsistencies that you speak
of, that you've delineated on this viewgraph, would be
eliminated with the issuance of the regulatory guidance and
documents and the standard review plan sections that we
talked about?
MS. DROUIN: I think the bulk of them would be.
When we went through, I believe it was Mr. King who spoke to
this yesterday, and we talked about NUREG-1602 which goes
through and systematically, you know, gives the attributes
of, for lack of a better word, of a quality PRA.
. 41
We started that in NUREG-1560 and we actually
broke down the PRA, you know, starting with your level 1,
your level 2, your level 3, and then, looking at each of the
different levels, what are the different tasks associated
with doing that part of the analysis. And if you're looking
at, for example, one task would be your initiating event
analysis, regardless of what -- the application or the
reason you're doing, if you just wanted to do a very high
quality PRA and given the current models and methods, what
do we mean by that?
CHAIRMAN JACKSON: I understand.
MR. HOLAHAN: In addition to that, even if there
were areas for which changes or improvement were made, using
the regulatory guides I think would highlight those areas
where there were differences and give insights, both to the
licensee and the staff of the limitations of the tool that
they've got.
MR. HODGES: And also, NUREG-1602 is not a
requirement. It says here's what we think would be a good
way of using the state-of-the-art technology to do an
analysis; and if you were reviewing one and they had already
used their bounding assumptions and analysis, you're not
going to make them go back and change. So you won't
necessarily eliminate this, but you might constrain.
CHAIRMAN JACKSON: What it does is it says -- it
. 42
constrains what the use is.
MR. HOLAHAN: Yes. Exactly.
CHAIRMAN JACKSON: How much you can rely on that.
MR. HODGES: Yes.
MR. HOLAHAN: Yes.
CHAIRMAN JACKSON: And that's really what it says.
MR. HOLAHAN: Probably the first and the most
important step is understanding the tool that you propose to
use.
CHAIRMAN JACKSON: Right.
MR. HODGES: Yes.
CHAIRMAN JACKSON: Right. Exactly. Okay.
MS. DROUIN: When we start looking more at these
models and methods, as I said, where we really saw
tremendous inconsistency, not incorrectness but
inconsistency, was in, you know, primarily the scope and the
boundary conditions and the assumptions that were implied or
-- not implied, I'm sorry -- used by the various analysts.
The one area that I probably would highlight would
be the human reliability. There were a couple of things
that we did see here. Certainly again was inconsistency in
the identification and selection of what human actions to
model, and then inconsistency in the implementation of the
various methods.
. 43
The last one was certainly there are types of
errors that the current methods do not cover when you start
looking at errors of commission, those things that the
operator elects to do on his own, not that he has failed to
implement but that he thinks he's doing the right thing but
he does the wrong thing. Those types of errors are not
currently modeled which could have some impact on the final
results in terms of identifying what are going to be the
dominant sequence and contributors.
CHAIRMAN JACKSON: Did you identify any methods or
models that should not be used?
MS. DROUIN: No. No.
MR. HODGES: I think, you know, we found at least
as wide, maybe wider variability in application of a
specific model as we did between models on the human
analysis.
MR. THADANI: I guess one -- I know of one plant
IPE, when they first came in, they assumed that the
likelihood of human error is zero in recovery acts.
MR. HOLAHAN: Yes, I remember that.
MR. THADANI: Zero. And of course that required a
lot of interaction.
CHAIRMAN JACKSON: Say that again.
MR. THADANI: There was one IPE that was submitted
which was based on -- analysis was based on the fact --
. 44
their judgment that their operators will not make errors at
all, probability is zero. That was a submittal.
CHAIRMAN JACKSON: I see.
MR. HODGES: That's one of the five that the
evaluation is not written yet.
[Laughter.]
MS. DROUIN: Again, that was sent -- you know, I
mean, the way I was focusing on was the actual method. That
was not a method; that was --
CHAIRMAN JACKSON: I understand.
MS. DROUIN: They had an assumption.
Okay. Slide 12, please.
We were asked to look at the IPE results as they
compared to the Commission safety goals. In doing this, you
know, there are several concerns or issues. Primarily the
IPEs are internal events at full power looking at core
damage and containment performance only. So we do not have
a level 3 analysis which carries all the way out to risk
looking at off-site health consequences.
They also don't include lower power and shutdown.
They don't include external events. So this is looking at a
very narrow part of the risk when we provide the insights
here.
The first thing we did was to look at the two
numerical objectives, the core damage frequency of 1e minus
. 45
four per reactor year and the conditional containment
failure probability of .1.
When we looked at the core damage frequency, we
saw that the core damage frequencies for the boilers all
fell below the 1e minus four. Most of the PWRs fell below
the 1e minus four, but there were several plants that were
above the 1e minus four.
COMMISSIONER DIAZ: Could you say what most means?
Ninety percent? Ninety-five percent?
MS. DROUIN: I think it was like 10, 15 percent if
you look at it on a unit basis.
CHAIRMAN JACKSON: When you talk about based on
point estimates, this kind of relates to the question I
asked yesterday. Is it based on propagating mean
probabilities through the, you know, the fault tree, or is
it based on carrying forward actual probabilistic
distribution?
MS. DROUIN: Yes. As far as we can tell from the
IPEs, what they reported to us were point estimates.
CHAIRMAN JACKSON: So you multiply this .5 by this
.4 by this .2 by this .1 as opposed to really carrying
forward the full distributions?
MR. THADANI: And one would not call these mean
values.
CHAIRMAN JACKSON: Okay.
. 46
MR. THADANI: They're not really --
CHAIRMAN JACKSON: They're really -- when you say
point estimates, you must mean that, that you multiply point
--
MS. DROUIN: I think most of them are point
estimates. I don't want to say absolutely.
CHAIRMAN JACKSON: No, but I'm saying, most of
them --
MS. DROUIN: But I think most of them are. They
didn't tell us differently.
CHAIRMAN JACKSON: And so when you calculate a net
core damage condition -- core damage frequency, you're
multiplying everything along the sequence?
MS. DROUIN: That's correct.
CHAIRMAN JACKSON: Okay.
MS. DROUIN: That's correct.
CHAIRMAN JACKSON: Yes, Commissioner McGaffigan.
COMMISSIONER McGAFFIGAN: If you were to do a 95
percent confidence interval, your guesstimate, knowing that
they haven't done it, how many plants would have part of
their 95 percent confidence interval below 1e ten to the
minus four?
MS. DROUIN: I think that you will certainly see
some of these above -- I'm going to answer a little bit
differently -- above the 1e minus four because you saw quite
. 47
a few of them that are right at the line.
COMMISSIONER McGAFFIGAN: So an awful lot right at
the line, so therefore if you have any sort of normalized
distribution, part of it's going to be below the line.
MR. HOLAHAN: It's a little dangerous to guess.
My guess is that most of the PWRs, the 90 percentile, the
95th percentile, would be able ten to the minus four. The
boilers might be below, but most -- it's hard for me to
think that most of the PWRs are in the middle or upper range
of ten to the minus fives and that the tail of that curve is
not above ten to the minus four.
MR. THADANI: It -- I'm sorry.
CHAIRMAN JACKSON: Commissioner?
COMMISSIONER DIAZ: I was going to say since, you
know, we have, say, ten to 15 percent that do not meet the -
- do not go, you know, one times ten to the minus four, did
we look at whether there was a generic cause for that?
MR. THADANI: Yes.
MR. HOLAHAN: Well, I think the presentation in
the report puts plants into categories and deals with issues
in categories, and I think that's probably the best way of
addressing what is it that makes some of the numbers higher
than others.
MR. THADANI: If you -- well, basically, on --
let's talk about PWRs, for example, and I have a class of
. 48
plants in here. It shows that if you -- by and large, the
key contributors are station blackout and transients. And I
would expect that means that the auxiliary feedwater system
is playing a very important part in those designs. So you
could then glean, if you took the next step, glean that kind
of information from these.
You have --
MS. DROUIN: I mean, if you want to compare here,
you can see the distribution.
If you look -- well, unfortunately I don't have a
back-up slide on this, but there's a figure in here that has
plotted the 1150 results, the main versus the distribution
from the 95th to the 5th, and plotted against it are the IPE
results. The IPE results, if I look at the PWRs and if I
look at the biggest spread, which is Sequoyah 1150, which
goes from about 2e minus seven all the way up to about 2e
minus five, you see the spread of the IPE results going
outside that spread just on the core damage frequency, and
you see the same thing on the boilers.
In fact, on the boilers, you see that there's
quite a few that are even -- quite a few -- I don't know --
at least a dozen that are above the 95 percentile of the
highest plant, the boilers in 1150.
CHAIRMAN JACKSON: Okay. Why don't you go on.
MS. DROUIN: Okay.
. 49
MR. THADANI: I did want to make a comment, and
that was yesterday when you asked us a question about how
many plants may be approaching safety goals and we gave a
response that there may be some, this is what I would call a
fairly crude analysis, and what this says is -- leaving
aside the issue of at what confidence level should we
discuss this issue of safety goals and so on, what this says
is the judgment was made if you had mean values and the
frequency of early containment failure is less than ten to
the minus five per reactor year, assuming all the analyses
are credible and so on, then I think generically enough work
has gone on, one could say that in that case, one would not
be challenging the safety goals, the early fatality
criterion which would be controlling basically.
The difficulty here is that what we have got is
very, very approximate calculations, and in order to really
give a solid answer to a question like that, I think one has
to dig a little deeper to be able to say how close are some
of these plants or do they exceed these quantitative goals,
and that statement then has to be tied with what kind of
confidence we have in that particular statement, whatever
that confidence level might be, and we don't have that
information as yet. And it's very difficult to do at this
stage from these studies.
MS. DROUIN: And that serves as a great
. 50
introduction to the next slide.
CHAIRMAN JACKSON: Before you go, if I look at the
containment failure probability --
MS. DROUIN: Yes.
CHAIRMAN JACKSON: -- do you have any sense of how
the numbers would go if you had a more full scope results
where you would explicitly consider seismic events, et
cetera?
MS. DROUIN: I mean, it's going to be on a plant-
specific basis, but, you know, you --
CHAIRMAN JACKSON: It's going to drive it that
way.
MS. DROUIN: Primarily, yes.
CHAIRMAN JACKSON: All right. Okay.
MR. HOLAHAN: I think you also get into one of the
inherent difficulties in using conditional containment
failure probability. It's very hard to define what that
really means.
CHAIRMAN JACKSON: Exactly.
MR. HOLAHAN: Which earthquake are we talking
about?
MR. THADANI: I think by and large if -- based on
at least the studies that have been done to date, the early
containment failure -- there's some I'd say unique
characteristics of severe accidents that tend to challenge
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containments. If you look at Mark I and Mark II plants,
they are inert. They're very -- the containments are very
small, and if you had a severe accident and if these
containments were not inert, hydrogen would be the real
cause for failure of the containment, probably fairly early
in the accident.
However, for Mark I containments, the most
significant challenge early on is a potential for the liner
melt through. It's like a light bulb. If you have a corium
coming down into the lower cavity, it will spread out, very
hot, attack the metal, and it will be the failure of the
metal liner.
The way to deal with that problem is very simple,
actually. A lot of work has been done. One needs to make
sure there's a way to get water, a layer of water on top of
the corium. Commissioner Rogers remembers this very well.
And in the IPEs, I believe, all licensees have now got
procedures to find a way to get water in, and that takes
care of that early challenge.
Similarly, the -- another challenge of great
concern for large, dry containments was the direct
containment heating issue.
Which research seems to show is not a real
significant -- I think hydrogen for mark three containments
is still a real issue. Mark three containments have
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igniters but these igniters are powered by off-site power
source so there may be a question about some similar
accidents, whether the igniters will function or not and
could lead to potential for early containment failure.
So I guess what I am getting to is that because
the challenges are sort of unique of that nature, I am not
sure that seismic would be a big issue. Fires could be
because fires can cause station blackout or other kinds of
scenarios.
CHAIRMAN JACKSON: I just used that to capture the
generic fires, you know, et cetera. Whatever.
MR. THADANI: Fires could be.
MR. HODGES: Another bias in some of these IPEs is
many of them did not take credit for some of the research
that has been done on things like direct containment heating
so they are getting actually worse results than you would
expect.
CHAIRMAN JACKSON: Yes.
MS. DROUIN: Looking at the quantitative health
objectives, you know, we looked at both of them, what was
your risk from your latent cancer which is not to exceed .1
percent of the total risk within 10 miles and what is the
risk from your prompt fatality which is not to exceed .1
percent within one mile.
When you look at these, both can be translated
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into numerical objectives looking at the latent cancer,
which implies the risk should be less than five e minus
seven per reactor year and for the early, which is implying
the risk should be limited to below two e minus six per
reactor year.
So looking at these numerical objectives, was
there some way to extrapolate from the IPE results against
those numbers? And, again, I want to say we have the same
issues and concerns because these were limited analyses
again in the sense of just addressing full power internal
events and they were not level three analyses, they did not
include, you know, the other aspects of risk and we are also
dealing with the point estimates. But was there some type
of crude screening thing that we could do to try and get,
you know, a feel for where we are against these objectives?
Well, the first thing we did is that we went back
to NUREG 1150 and recognized that the most limiting margin
in getting there was going to be associated with early
fatality risk. So since we are dealing with early fatality
risk, we then went and looked to see what are the dominant
contributors and your dominant contributors are associated,
you know, with your early containment failure and bypass.
Given that, we went back to the IPE results and
looked at what they were reporting as the frequencies
associated with early containment failure and bypass and see
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if we could screen at that, what was a threshold level that
we could screen at if they were below that level. We could
sort of get a feel that they were not going to approach
these objectives and looking at that we were able to assume
or guess as the threshold of about one e minus five per
reactor year. So if those frequencies fell below that, we
felt comfortable in screening those plants. At that point,
we were able to screen out about 79, 80 of the units fell
below that one e minus five and that left us about 29, 30
units that were above it.
So then we said, well, given that, was there
another gross back-of-the-envelope type calculation that we
could do real quickly to try and get a feel where these
remaining plants fell and there were several things that we
did.
We first went and looked at the release classes
that were reported in the submittals associated with early
containment failure and bypass and we looked at the source
terms that were associated with the early containment
failure bypass release classes in looking at the release
fractions that would give rise to an early fatality, looking
at what the release fractions were for iodine, cesium and
tellurium and then seeing if they were above -- if they were
above a certain threshold it could give rise to this early
fatality.
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So then we went and took that information and then
we tried to then account for the population. In looking at
about one-third of the sector's population out to about one
mile, that translated into a certain thing and through our
back-of-the-envelope calculation real quickly, what we came
out of is that there are another 15 plants we could screen.
But it looked like we had about 14 plants using, you know,
their source terms and release classes and then doing this
crude approximation, we had about 14 that may approach this
numerical objective of the two e minus six per reactor year
for your early fatality which, as Mr. Thadani was also
saying, I'm not trying to say this is very, very crude. It
just sort of is a flag to point of where we might need to go
look some more in depth.
MR. THADANI: I might just note that what Mary is
talking about is discussed in volume two, section 16 and it
starts at pages 16-3 and goes on to 16-11, sort of the
process that we went through.
COMMISSIONER DICUS: Before you go on?
CHAIRMAN JACKSON: Sure.
COMMISSIONER DICUS: I guess obviously, given even
all the qualifiers you put on confidence in these numbers,
it is still a little disturbing to have a document that says
possibly based upon the staff's extrapolations of uncertain
data. I think I have that all right, 14 plants may approach
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this individual early fatality objective. That is somewhat
disturbing to have this and, I guess, go forward and perhaps
it is in some of the documents that I haven't reviewed but
what are you going to do about this? What's the next step?
It might be important to talk a little bit about that at
this point.
MS. DROUIN: Mr. Holahan is going to talk to all
of that.
MR. HOLAHAN: Thank you.
COMMISSIONER DICUS: Had you planned on that?
[Laughter.]
MR. THADANI: No, frankly, we do want to make
sure. I think there are ways to screen out. I think one of
the areas we have discussed, we must follow up on, is all of
those plants which are showing frequency of early
containment failure of greater than 10 to the minus five, as
a way to screen, make sure we are looking at those plants.
I would make another note. And if we want to
impose the backfit, reduce, we will go through our process,
substantial improvement in safety through regulatory
analysis guideline and cost/benefit analysis to see how far
we can actually go.
MR. HOLAHAN: The point that we really --
CHAIRMAN JACKSON: Let's wait. If you are going
to speak to it, let's, for coherence, let her finish, if you
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don't mind.
COMMISSIONER DICUS: No, that's fine, we may come
back to it.
CHAIRMAN JACKSON: Then we can come back and have
a complete discussion.
MS. DROUIN: The next one kind of goes on that
same theme in the sense -- well, let me back up. Let's go
to slide 14.
We were also asked to look at, you know, what we
say in terms of the station blackout rule, what kind of
impact that it has had on core damage frequency.
As we were asked to look at the safety goals, we
had problems here too because, again, we were trying to us
an analysis. This was not the purpose of it and to glean
what we could from it.
When you do look across all these plants, you saw
a tremendous variety in the coping methods that were adopted
as a result of the rule. But now when we are trying to
assess, you know, what has been the impact and we are trying
to glean this from these submittals, the problem came is
that a lot of this information that we needed is simply not
in the submittal and we only had about 15 percent of the
licensees that told us the before and after picture. You
know, here was their core damage frequency before the
station blackout rule and here was their core damage
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frequency after the station blackout rule.
In looking at that, you know, you saw an average
reduction of two e minus five. And so if you are looking
just for the impact, using a very small sample, you do see
reduction that has been a result of the station blackout
rule.
The other thing was to look at, you know, what was
the actual credit and what I mean by that is that, although
we might not have had the before and after, we had a larger
sample in that licensee's totals that they took credit.
They might not have told us the before CDF but we knew that
the core damage frequency that they reported they told us
that they had implemented the station blackout rule and it
was credited in there.
So when we go back and look at that sample of
plants, that was about I think 60 percent of the plants, but
don't quote me on that. I am doing that one off the top of
my head.
You saw that the vast majority fell below the goal
of the one e minus five per reactor year but you did see
some plants that had implemented the station blackout rule
that were still above the one e minus five. I think it begs
the same question.
Here, and I don't want to preempt Mr. Holahan,
because we are working very closely with NRR and trying to
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identify the selection criteria of what activities we are
going to pursue. I think NUREG 1560 serves as the first
step in pointing to some things but, you know, how we
proceed forward, I think you have to come up and decide, you
know, what criteria you are going to use in pursuing based
on these insights and perspectives on some of these plants
that are coming out of the document.
CHAIRMAN JACKSON: How many licensees have, in
fact, implemented the station blackout rule?
MR. THADANI: I can confirm but I believe it is
100 percent.
CHAIRMAN JACKSON: All right.
MR. THADANI: The rule is --
CHAIRMAN JACKSON: I am just looking at what the
next-to-the-last bullet said. For those licensees that had
implemented --
MS. DROUIN: Right because, again, we are basing
this on the submittal which is 1990.
CHAIRMAN JACKSON: All right.
COMMISSIONER ROGERS: Do we have any numbers of
the average cost in dollars per person rem averted in
achieving that average reduction of two e to the minus five?
Can we see what that cost to do that?
CHAIRMAN JACKSON: Can you capture? I mean, is
that data available?
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MR. THADANI: We could -- we can approximate it.
We have --
COMMISSIONER ROGERS: It is just a ballpark number
as it is. How does this compare with it?
MR. THADANI: We could probably estimate it could
be on the order of what I am probably giving I would suspect
is a conservative maybe 200 person rem per year per plant
because if I -- what I am doing is I am making an assumption
here that station blackout is going to lead to a substantial
release and I am using some old siting source term studies
data to try and estimate. But we can give you a much better
estimate.
COMMISSIONER ROGERS: I think it would be
interesting to see how that works out, you know.
MR. THADANI: We can do that. We will do that.
MR. HOLAHAN: I think the risk part --
CHAIRMAN JACKSON: I just want to know, given the
station blackout rule, is station blackout still the
dominant contributor to core damage?
MR. THADANI: It appears to be from most of the
studies, still a dominant contributor to core damage.
MS. DROUIN: But I would also add, you are always
going to have something that contributes to risk and the
question is, is it coming down, is it coming down.
CHAIRMAN JACKSON: You were about to make a
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comment?
MR. HOLAHAN: I was going to say, I think we have
a substantial amount of information about a station blackout
analysis but the costs associated with station blackout or
reducing risks, I think there is very limited information
available.
MR. THADANI: We provided the Commission some
information on costs a few years ago on station blackout and
I thought your question was more on the averted risk in
terms of person rem.
COMMISSIONER ROGERS: Yes, right. We can convert
it to that measure.
MR. THADANI: We can try and get that.
MS. DROUIN: Slide 15, please.
As we said, we did have a workshop back in April
in Austin, Texas. We had three objectives that we had
stated very clearly at the beginning of the workshop that we
had given to all the attendees. What we were trying to
achieve was, one, get feedback on the accuracy of the actual
information and data that was in the NUREG. Also, get
feedback on the perspectives and insights that are discussed
and also get feedback on the potential uses of the results
and the perspectives that are discussed and that's what we
went forward with during the three days and had a lot of
discussion on.
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When you look at the workshop it was attended by
various utilities, all the owner groups, EPRI and NEI was
there. Tremendous comments we received, primarily focusing
on the first objective was what we really got, so the
accuracy and information of the data and that led to the
third bullet down here where we had a general concern that
the information in the NUREG is out of date and what do we
plan to do with that.
When I look at the second objective, in terms of,
you know, what feedback could we get on the perspectives
that were in the NUREG, we really didn't get any kind of
what I would say negative feedback in the sense that what we
had presented was incorrect. It was more, really,
associated with information is out of date and then because
it is out of date, how does the NRC plan to use this? And
those two concerns kind of fed each other.
Our plans right now for NUREG 1560 is that we are
not going to go back and rewrite this NUREG with the updated
information for several reasons. One is that we don't have
the information. We have very -- we have a scarcity and it
is not as simple as just getting the core damage frequency
numbers. You need the core damage frequency numbers, you
need the accident sequences, you need the contributors, you
need the -- I mean, it goes on and on and on. The only --
we did not just look at that bottom line number in coming to
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the perspectives and insights that are reported.
You then go to the next question, is that, you
know, these PRAs are going to keep evolving, keep updating
and the conclusions that we really have here on a global
basis, I think, are still pretty valid. They are not going
to be, of course, on a plant-specific basis and that's the
regime, the realm we're moving into. It might come back,
maybe, years down the road or sooner down the road that we
revisit that. But at this point in time, it is not our plan
to go and update this with the information.
We do plan on citing to a NUREG where we have some
updated information in it but we aren't going to disregard
that. There is some updated information that has been
provided to us and what has been will be cited in there. We
will also provide an appendix of the summary of the public
comments and our staff responses to it.
At this point, I will turn the presentation over
to Mr. Holahan.
CHAIRMAN JACKSON: Do you have all the questions
to ask -- I mean the answers to what the Commissioners just
said? We hope you've been keeping the list.
MR. HOLAHAN: I did write down some.
COMMISSIONER DICUS: Yesterday, it was, you know,
"That question will be answered tomorrow."
CHAIRMAN JACKSON: That's right. Remember I said
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we'd come back to you on this.
COMMISSIONER ROGERS: I hope you remember those
questions.
MR. HOLAHAN: Slide 16, please.
CHAIRMAN JACKSON: That's the answer, second
bullet.
MR. HOLAHAN: I thought I would cover some of
these through the presentation, then I have a list of things
that I don't think are quite covered in the presentation I
will try to address, okay?
One of the issues is the use and the relationship
between 1560 and other ongoing activities, and the insights
derived from the IPE program and the review of those IPEs
has been used in developing the regulatory guides. Although
much of what's in the regulatory guides is really regulatory
philosophy, you see a lot of the technology issues are dealt
with in the reference document NUREG-1602, and there are a
number of sections in 1602 that derive the technical
insights directly from the IPE program. So, in fact,
there's a lot of overlap between a few of the chapters in
NUREG-1560 and sections of NUREG-1602.
Not only did it give us ideas of what constitutes
state of the art, but it gives us an idea of the various
methodologies used by licensees. So that's reflected in
1602.
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Neither 1560 nor 1602 are really the regulatory
guide. I think in the long-term, we'll consider 1560 to be
the counterpart to the IPE program. It's sort of the one-
time snapshot of the licensee's evaluation of those plants
and the summary of that activity is what's in 1560.
What was learned from that program I think will be
preserved in the regulatory guides and its reference
document, which is NUREG-1602; and I think as we learn more
about the technology and the state-of-the-art expanse, I
would expect that not to result in another version of 1560,
but perhaps a revision to NUREG-1602. So that -- and I
think in the long-term, as was mentioned yesterday by Tom
King, the staff is looking at the possibility of developing
industry standards on doing PRA type analysis, and that
would either take the place or reference a document, a
state-of-the-art document like 1602.
The 1560 insight document has provided information
for the staff for a number of uses, and I think I'll just go
ahead and cover that on slide number 17. Because there are
a number of follow-up activities.
As Mary mentioned, there were a number of plant
enhancements identified and modifications made as part of
the IPE program. Not all of them are called
vulnerabilities, but there were plant upgrades. But not all
improvements were made by all plants, and what we see from
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looking at the document is there was a wide variety of
results and a variety of decisions that were made by
licensees as to what enhancements to put in place and which
ones not.
I think this raises the possibility that the staff
will look at those areas where some licensees decided that
an enhancement was, you know, a valuable contribution to
safety, but where the decision wasn't made on a comparable
plant, I think we want to back and understand why those
decisions were made. So that's one area where the IPE
program will be useful in identifying or screening for
potential safety issues.
I will go on and cover the other regulatory
activities as I go on.
One of the things we need to do is to take the IPE
results and look at them and identify what sort of areas do
we want to follow up on. I think you've heard a number of
discussions today that there's sort of the natural tendency
to say, well, if a plant is above ten to the minus four,
maybe we should look at it. But we've identified a slightly
different approach, which is -- and this is still on the
development, and I think we owe the Commission a paper on
how we're going to do this later in the summer. I think
it's August, July or August.
MS. DROUIN: September.
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MR. HOLAHAN: Or even September.
And one of the things we've begun to think about
is since the reason we're looking at this is for potential
improvements to the plants, those improvements are really
made in specific areas and on specific issues. So the fact
that the core damage frequency, the total is high really
doesn't tell you what you want to know about whether an
improvement would be cost beneficial.
So what we decided to do is to pick a screening
criteria which is much closer to the regulatory analysis
guidelines for what you really want to know and what the
regulatory analysis guidelines say is if you can identify a
given issue or a given change to the plant which would
produce a ten to the minus five improvement, that would be a
substantial improvement. So that's the first screening
test.
So what we thought we would do is go back and
identify individual sequences above ten to the minus five
rather than a plant above ten to the minus four, because
those sequences might identify given pieces of equipment or
given procedures or activities where you might be able to
make improvement to drive the risk down.
Now, obviously the further above ten to the minus
five, the more potential for improvement there is. So
that's one of the places we'll start looking.
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The others are in addition to using the numbers
that are in your report, I think we have to ask ourselves,
do I believe all of the numbers and should I be just using
those answers? So one of the things we'll be looking at is
the distribution of results. And when you page through the
insights report, you'll see on a class of plant sort of
basis, there's quite a lot of variability, one plant to
another, on both the risk and the large early release
frequencies.
So we will be looking at those outlier plants more
than those that tend to be sort of in the center of the
distribution and what we want to know is why the ones that
are high are high, are there really physical differences in
the plant or plant activities that are making it different
from other plants, because if there are things that many
plants can do and a few plants are not, then at least we
know that there are feasible changes or potentially
practical changes that could be made to those plants to make
them look like the others. So at least it's a screening
criteria to get a collection of plants and issues that can
be looked at.
Really what we're interested in is using this
information to make potential safety improvements if they
meet the backfit rule requirements for being substantial
improvements and justified by cost.
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In addition to looking at the plants that appear
to be sort of higher than their counterparts, we're also
going to look at those that are quite a bit lower, and I
think what we hope to learn from that is either they have
some brilliant solutions to safety issues which I think we
would like to understand, or else there's something unusual
in their analysis that says maybe I ought not to believe
that they really are that different.
So I think we're going to look at the outlier
plants and the issues that are above ten to the minus five.
CHAIRMAN JACKSON: But it also implies, does it
not, that in looking at the outlier plants, you really have
to have an updated -- I mean, what you -- you know, if
you're relying on analysis that you told me is seven years
old, that presumably there could have already been changes
and updates to the analysis that would not have them be such
outliers.
MR. HOLAHAN: Yes.
CHAIRMAN JACKSON: Look at them as a crude screen
to start.
MR. HOLAHAN: Yes. Well, unfortunately, it's the
only database we have at the moment.
CHAIRMAN JACKSON: No, no, no. I agree with that.
When I say crude, I mean coarse screen.
MR. HOLAHAN: Yes. So I think we do understand
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that.
CHAIRMAN JACKSON: Okay.
MR. HOLAHAN: What that means is that really it is
only the first step in the screening process.
CHAIRMAN JACKSON: Sure.
MR. HOLAHAN: And then I think, rather -- one of
the things we talked about was the difficulty of going back
to all licensees and asking for all of this information over
again, but, in fact, if there are a handful of plants and a
handful of issues, then we can go to the licensees and say,
"Does this really reflect your current understanding of the
plant?" And we can deal with a much smaller set of
information.
There is an additional item that we're interested
in following up on, and frankly we haven't cited exactly how
to deal with it, but we realize that the IPE program has
produced something I think somewhat unusual, which is the
plants that started this process meet their regulatory
requirements. The enhancements that they are making are
really beyond the minimum regulatory requirements, and
almost by definition, those are not controlled by any
regulatory process. In fact, there's nothing in the process
that says a licensee couldn't remove the enhancement they
put in a few years ago if they get tired of doing it next
year.
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So what we see is we have a situation in which
there may be enhancements put in the plant which both we and
the licensees think were very worthwhile doing, and yet they
are possibly or maybe likely not to have been captured in
any way in the current licensing basis of the plant. So the
first step we want to do is go back and understand the
status of improvements put into the plant, and then I think
we have a regulatory decision to make or maybe even a policy
decision for the Commission to say once we understand what
these are, and if they are important safety issues, should
they be controlled by some sort of regulatory process?
Should they be listed in the FSAR, for example, and so
they're controlled by the 5059 process? Should the
Commission in fact require licensees to continue to provide
those enhancements?
So it's -- I think that's an issue that we're
going to need to come back to. It isn't clear at this stage
what we should do with it, but I think it's an important
issue that we need to follow up on.
Can I go to slide 8? In addition to finding
plants for which some safety enhancements may be worthwhile,
we may find some potential safety issues of a generic nature
that need attention.
Now, I think this is less likely than the plant
specific issues by the very nature of the IPE program. It
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was by its nature the search for plant specific information
and we are more likely to find that it is plant specific
variations or plant specific features that are important or
should be required than we are likely to find, you know,
broad generic issues that need to be addressed.
Now, the reactor coolant pump seal issue I think
is a possible exception to that, although it's possible that
it may be more important on some plants than others and, in
fact, could be dealt with on a plant-specific basis. But it
is an example of an issue that does come up in a number of
the analyses, that it shows up to be important, and not just
in one place in IPE, but it shows up as being important in
the station blackout analysis and in a number of transients.
So it's one of the subject matters that we'll probably be
following up on.
COMMISSIONER DIAZ: Can I ask a question?
CHAIRMAN JACKSON: Please.
COMMISSIONER DIAZ: I'm just trying to understand
the depths of this. For example, you talk about BWR reactor
coolant pump seals. Are issues like, you know, stress
corrosion, cracking in recirculation lines in BWRs, which
used to be, you know, an issue we always talked about, will
that show up in this analysis?
MR. HOLAHAN: I don't think so. But it won't show
up because the analysis doesn't show it to be important. If
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the analysis showed that this was a dominant issue on
boiling water reactors, then it will say -- well, I think
it's sort of the same as the station blackout issue. We
dealt with this years ago, but why is it still dominant?
But to the extent that things are not dominant, I think they
will pass by.
COMMISSIONER DIAZ: Okay.
MR. THADANI: I think that is a very important
question, I think, because it raises some other types of
issues because of the way the risk studies are actually
done, experiential database, and we've talked a little bit
about in-service inspection yesterday.
And since we're on the station blackout issue, as
you know, in the BWRs, the steam generator tube capability
at certain temperature and pressure conditions is also a
concern, an issue that is being studied currently as part of
the steam generator activity, and to the best of my
knowledge, and maybe Mary can correct me, I don't believe
any IPE or PRA has addressed that sequence potential for a
steam generator tube failure given high pressure, high
temperature conditions in the primary system.
CHAIRMAN JACKSON: Are you looking at ATWS?
MR. THADANI: ATWS is also one of the issues that
we're reassessing besides station blackout, yes.
COMMISSIONER DIAZ: But I think it is clear that
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there are certain issues that are laying out there that have
not been addressed.
MR. THADANI: That's right. Yes.
COMMISSIONER DIAZ: Thank you.
MR. HOLAHAN: In addition to the potential
regulatory uses that I've discussed of the IPEs, I think
it's an important area where we can learn about issues that
need some research activities, and when something is
important in the IPEs, I think that -- in the PRAs that go
along with those, then I think those are areas where we may
want to make improvements and push the state of the art.
I think all these PRAs say that human analysis is
important and it's an important contributor to the
uncertainties as well. I think the research program already
recognizes that and I think this just reinforces, you know,
that additional work in that area is important.
Core damage prevention strategies -- for example,
the use of this information in severe accident management
guidelines or improving PRAs, I think as you mentioned
earlier, the -- for example, how core damage is modelled, I
think these are potential areas for research both sort of in
the basic research, understanding the phenomenon better, and
also in the modelling sense of including these in sort of
the state of the art of probabilistic risk assessment.
COMMISSIONER DIAZ: Excuse me. Does this mean
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that the early containment failure you feel like has been
resolved and doesn't need to be considered as one of these
issues?
MR. HOLAHAN: Well, I think it depends on which
mechanism for early containment failure we're talking about.
I think some have -- some have been resolved fairly
convincingly, but I also go back to what Wayne Hodges
mentioned earlier in that in the level 2 analysis, I think
these analyses are not quite state of the art, and so I'm a
little bit reluctant to -- I think you want to draw what
information you can from them, but I would be a little bit
reluctant to have these analyses, which I think are behind
the state of the art, directing the research program. In a
sense, I think the research program has led our
understanding of core melt progression and containment
performance, and there probably isn't a lot from the IPEs
that the research community doesn't already know.
COMMISSIONER DIAZ: Okay.
MR. THADANI: I think the only point I would make
would be the idea -- the two key elements: first,
prevention of core damage is fundamental; and second, do we
understand accident management enough to try and see if
molten material can be retained in vessel. I think those
are -- if we can come to some conclusion on that, that would
indicate the actual risk of public health and safety is much
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lower than what we are calculating today with these models.
COMMISSIONER DIAZ: It certainly will relieve the
containment damage, yes.
MR. HOLAHAN: The last prepared section is the
fact that IPE results can be used to prioritize inspection
activities, not just in a broad sense, but also on a plant-
specific basis where there are sequences, equipment and
activities on a given plant that the licensee has identified
as important. I think these are clearly candidates for
increased inspection activity or focusing the existing
inspection activities.
CHAIRMAN JACKSON: Well, with respect to these two
bullets, I mean, to what extent have inspection activities
already been prioritized by risk?
MR. HOLAHAN: Well, I think as Mr. Callan
mentioned earlier, I think it's an ongoing process. I think
we've begun doing that.
CHAIRMAN JACKSON: Is there a guidance out there
to that effect? Is that part of some core -- I mean, how -
- what do you mean when you say you --
MR. HOLAHAN: Well, there is -- in the PRA
implementation plan, there is -- a folding of risk insights
into the inspection program is one of those activities, and
I think some of it has been done, but I think there is more
being planned, also.
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CHAIRMAN JACKSON: Let's hear from Mr. Callan.
MR. CALLAN: Several of the major inspection
procedures, what I would call kind of the bread and butter
procedures that, for example, that the residents use, direct
residents, inspectors, to use risk insights to select smart
samples when selecting maintenance activities. Given the
range of maintenance that may be going on in a day, they
only have resources to look at maybe one or two items.
Operational activities. Every day, they have to triage what
they look at, what they get involved in, and risk insights
are used.
Of course, the issue is what I mentioned earlier,
Chairman, and that is that that presupposes that they have
the expertise, the sophistication to make wise choices.
CHAIRMAN JACKSON: In what they are making use of
in making those selections.
MR. CALLAN: Right.
CHAIRMAN JACKSON: What tools they're --
MR. CALLAN: Right.
CHAIRMAN JACKSON: Aside from their own
sophistication. Are they using PRAs or insights from IPEs
or what?
MR. CALLAN: I'm going to have to give you
somewhat of a parochial perspective, a Region IV
perspective, but I think this is representative. I would
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say essentially all the inspectors, all the residents and
region-based inspectors have undergone at a minimum the
three-day PRA course, most of them the one-week course, and
several the two-week. So they've all been trained and they
all -- I won't say all -- most residents' offices will have
the IPE on their bookshelf available to them.
CHAIRMAN JACKSON: Five years old though it may
be.
MR. CALLAN: Yes. But I suspect, though, that
most savvy residents tap into the licensee's risk process.
Some have risk meters, as you know, and other similar types
of methods for monitoring risk day to day and during
outages, and I think most inspectors will in a sense
plagiarize or use that information. It's --
CHAIRMAN JACKSON: But at this point, we can't --
in the sense of the bullets on the slide, we haven't started
doing it totally systematically and there's not consistent
guidance out there.
MR. THADANI: That's correct. Initial guidance
has been provided through our inspection branch in NRR
actually, and the two activities underway, as Gary
mentioned, one is revision of manual chapter 1145 that's
going to include what I would call much more detailed
guidance on the use of risk insights. In parallel, AEOD is
working on training aspects and there is a pilot course
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that's being developed. I believe it's going to be -- it's
going to be resource intensive, I think, about two-and-a-
half weeks long probably. That pilot I believe is within -
- it's either this month -- later this month, I think, and
by the end of September, I think, we're supposed to finalize
that course and start giving it to people.
I think that will go a long way towards at least
addressing the concern that Joe, Joe Callan raised. One has
to be savvy. You can't just give insights.
CHAIRMAN JACKSON: You're going to focus it on
inspectors?
MR. THADANI: Yes. That's part of the objective
of the course.
CHAIRMAN JACKSON: Okay.
MR. THADANI: And it will include reviewers as
well, yes.
MR. CALLAN: Let me give you a candid perspective,
and it's somewhat parochial, as I said. In general, though,
the licensees that the inspectors deal with are more
sophisticated than the inspectors are and more -- in terms
of use of PRA, and so in a sense, the NRC is at a
disadvantage in using this methodology and engaging
licensees on issues. They can bring more resources to bear,
more expertise to bear in rebutting an NRC perspective, and
that's a source of frustration. You know, you all visit the
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regions and interact with regional staff; you probably sense
that from your interactions. There is that -- something
that may be approaching an inferiority complex in this area.
COMMISSIONER ROGERS: On the other hand, they have
the licensee's PRA as a working document to look at and
guide their own inspection activities and leave it to --
MR. CALLAN: That's right, but there are, what, 75
stations or something like that, and each one of them
probably has in-house PRA capability that equals that of the
NRC. Each one of them.
COMMISSIONER ROGERS: Oh, yes.
MR. CALLAN: And exceeds that of any given region
by far. So --
CHAIRMAN JACKSON: Well, I think that it's a
comfort level, too, that I'm hearing and until and unless
people, particularly the inspectors, have this systematic
baseline training, there's going to be an extent to which
the comfort is not going to be there.
MR. HOLAHAN: I'll just summarize to say that what
I've given you is some examples of the use of the follow-up
on the IPE program. I guess the bottom line is really staff
intends to use the IPEs like other PRA information to focus
our activities on what's most important in a number of
areas.
Now, I did write down one question earlier and
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we'll see how far we can go in addressing it, and that is -
-
CHAIRMAN JACKSON: You've got two minutes.
MR. HOLAHAN: TWo minutes? Okay. Good.
How far will we go towards answering the question
of whether these plants exceed the safety goal or not, and I
think we will be addressing that at least in an indirect
way, and it's not exactly clear to me whether what we're
doing will completely answer that question.
When we look at plants that might have some
outlier issues, clearly plants that have large early
releases above ten to the minus five as Mary mentioned as a
sort of a screening tool, those will be captured. I think
it's pretty clear that plants there and the issues that
drive them there will be captured for our screening
analysis.
That will force us to go through additional
analysis. If you recall how the regulatory analysis
guidelines are established, there's a screening test that
looks at core damage frequency and conditional containment
failure probability. Those two together are somewhat
comparable to large early release frequencies. I think
these 14 plants will be captured as -- the issues that drive
them I think will pass that screening criteria.
The next stage is to do a value impact analysis.
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That is, after you go back to the licensee, to say, are we
really dealing with the right set of facts today? Then
after that comes a value impact analysis, and that value
impact analysis goes all the way to dose, and in that sense
it is a level 3 analysis capable of comparison with a safety
goal.
What I would think is that it's likely that plants
that have large early releases which result in doses as high
as, you know, some early fatalities will be candidates for
some improvements. If those improvements can be made at a
small or moderate cost, then I think the staff will just --
we'll deal with those on a plant and an issue basis.
Now, it seems to me that it is possible that there
will be some plants which are found to exceed the safety
goal but for which the staff and the licensee can't identify
any let's say what's obviously cost beneficial or cost
justified remedy to that situation.
Now, I think those are situations that might have
to be brought back to the Commission to decide what does it
really mean to have a plant which, you know, through further
analysis appears to exceed its goal but for which the staff
doesn't have any obvious remedy to the existing
requirements.
I think partly that's a policy question because
the original safety goal policy of the Commission was not
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that all plants should meet this, but that the industry as a
whole. And I think it may -- perhaps it shouldn't be too
surprising that, you know, some of the students are below
average. But I think that may be a situation that we'll
have to deal with sort of at a later stage of this follow-
up activity.
MR. THADANI: In fact --
CHAIRMAN JACKSON: Thirty seconds.
MR. THADANI: I think, in fact, it's very
important to know that the Commission gave strict direction
to the staff when we were looking at advanced lightwater
reactors that the staff should not impose requirements
beyond what could be justified in meeting the safety goals.
So on advanced lightwater reactors, while the real risk is
lower, but the staff requirements were based on not going
beyond the safety goal for advanced lightwater --
COMMISSIONER ROGERS: Well, there was some body
language in that and there was an expectation.
MR. THADANI: That's right.
COMMISSIONER ROGERS: There was an expectation
that the design would lead to results which were --
MR. THADANI: Yes.
COMMISSIONER ROGERS: -- about an order of --
MR. HOLAHAN: Yes.
COMMISSIONER ROGERS: -- magnitude better than the
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current designs without explicitly referring to the safety
goals.
MR. THADANI: That's how containment performance
goal was derived, actually.
CHAIRMAN JACKSON: Any further questions?
COMMISSIONER ROGERS: Do you mean on the whole
thing?
CHAIRMAN JACKSON: Yes. We're about to --
COMMISSIONER ROGERS: Yes. Sure.
CHAIRMAN JACKSON: We've been here for two hours.
COMMISSIONER ROGERS: A couple. I'll try not to
take too much longer.
You brought up the observation that the scope and
boundary conditions were really very important in giving
rise to differences between plants that were otherwise
perhaps rather similar to each other in terms of the -- I
mean, that's what I read into what you were saying, that
because the licensees picked the scope and boundary
conditions in doing the PRAs, therefore you get somewhat
dissimilar results, somewhat dissimilar results for
otherwise similar plants.
So I wonder if the next -- what thinking there is
in trying to go back and encourage some kind of uniformity
on that basis if PRAs are going to be used for other
purposes in the future so that we're taking a step or
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encouraging a step to go towards a more standardized
approach? It wouldn't totally standardize how they did
their PRAs, but at least those key items of scope and
boundary conditions might be -- might help to bring things
into much closer conformity.
MS. DROUIN: And I certainly think it would, but I
think, you know, you also have to ask the question, you
know, given what application and everything, how much of
that you really want to do.
The other thing I would also -- trying to
translate what you said, I don't want you to be misled that
the variability is completely driven by the scope.
COMMISSIONER ROGERS: No, I understand.
MS. DROUIN: You will not -- you will always see
variability in these results because the plants do look
different.
COMMISSIONER ROGERS: Yes.
MS. DROUIN: I just didn't want to say that it's
completely caused by plant design differences.
COMMISSIONER ROGERS: But it may be very important
in trying to arrive at something that's a little closer to a
common approach in getting at a bottom-line number.
MS. DROUIN: Right. But I just think you're going
to have to start thinking about, you know, the application
and the uses in determining what that standard should be or
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if it should be one.
COMMISSIONER ROGERS: Yes.
MR. HOLAHAN: I think in the guidance documents,
we tried to have some balance between the obvious desire for
high quality, consistent analysis and to allow licensees the
flexibility to use what they currently have as opposed to
having to wait until they have something else.
COMMISSIONER ROGERS: Yes.
MR. HOLAHAN: One would hope that licensees sort
of figure out that the reviews are simpler on the staff's
part and they're going to get more benefit from having a
more of the state-of-the-art analysis tool, but, you know,
we didn't draw our line in the sand to say if you don't have
this tool, you can't play.
COMMISSIONER ROGERS: Well, I just would remind
everybody that when we started out with the safety goals,
what they were designed to do, to make a very important
statement about average expectation; and now if we
substitute a surrogate for a safety goal, for a health
effect safety goal, and then start to look very carefully
and get very concerned if somebody doesn't quite meet that,
that's a change in point of view. I think that the
Commission ought to keep that in mind in looking at how far
we want to go, because the safety goals were regarded as a
definition of how safe is safe enough. That was really
. 87
where we came down on that issue.
The other point is a rather small one, but I just
think that in talking about numbers, we ought to be a little
bit more careful about how we throw them around. I happen
to disagree with you when you say 4.1 -- I mean, I can't
disagree with what you said as to how you would interpret
it, but, you know, to me, 4.1 times anything tells me that
in general practice, that's probably between 4.06 and 4.14
and not something else.
I think that there's a sloppiness here, not just
on our part, but there's an inconsistency with respect to
how we state these numbers and then how we look at
uncertainties and, you know, it's really quite sloppy. I
think that it would be well to try to exercise some
influence on a uniform approach to stating numbers.
You know, there are standards that people do apply
in this business -- maybe not in PRA, but in other
scientific endeavors -- where when you state a number and
it's got no decimal point after it, it means something, and
when it's got a decimal point after, it means something
else, and the number of figures after the decimal point
means something else.
I think we ought to revert back to standard
scientific practice here and try to see that there aren't a
lot of numbers floating around that really don't make a lot
. 88
of sense when you consider the uncertainties in them.
CHAIRMAN JACKSON: I agree with you, Commissioner
Rogers, completely, but I think the only way that one is
going to get at it in a realistic and honest way is to
finally grapple in the best way we can, with the state of
the art being whatever it is, with the uncertainty issues
and the confidence issues. They come up, Commissioner
McGaffigan raises them, I raise them in every meeting, but
the numbers in and of themselves don't mean anything if you
don't know something about the probability distributions on
which they're based, how those uncertainties and so forth
have been propagated through the calculation and that you
come out with a number that you can say with some certainty,
with a certain degree of confidence. If you don't do it
that way, none of the discussion makes sense.
So, you know, you can multiply .41 times .25 times
whatever and you can come out with a number. It doesn't
make any sense in this kind of context except in some very
generalized way. And, you know, I'm sure that Mr. Holahan
needs no defense, but I think that is the sense in which he
gave the wide range in terms of what he thought a particular
number meant.
COMMISSIONER ROGERS: Well, I certainly quite
agree with you, but I think the point is that, you know,
your final observation that, you know, it -- those numbers
. 89
don't make a lot of sense only within a certain kind of
range and we have to say that. I mean, that has to be part
of the statement.
CHAIRMAN JACKSON: I think that is, in fact,
covered, I hope, you know, at least in words, in your guides
document subject to more fleshing out in the public comment
process.
MR. THADANI: It is covered in the guides.
Yes, I do want to comment. There are certain
elements that one can develop distributions about, one can
talk about confidence levels. There are certain types of
uncertainties that you can quantify; others you cannot
quantify.
COMMISSIONER ROGERS: Yes.
CHAIRMAN JACKSON: That's right.
MR. THADANI: I think the comment you're making is
whatever the scope and the level of analysis when you're
describing a quantitative measure, you have to say it at the
same time with those boundary conditions around that.
CHAIRMAN JACKSON: That's correct.
MR. THADANI: And I think we need to --
CHAIRMAN JACKSON: I think that's what --
MR. THADANI: We're trying to do that.
CHAIRMAN JACKSON: That's why Commissioner
McGaffigan keeps asking you what do you mean by the
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difference between 4.0 ten to the minus five and 4.1 ten to
the minus five.
MR. THADANI: We're making -- that's an effort
that's reflected I think in the guides. We're trying to do
that.
COMMISSIONER ROGERS: Yes.
MR. HOLAHAN: I think we have a -- we have a real
notation problem.
COMMISSIONER ROGERS: Yes.
MR. HOLAHAN: I think normally two digits are
carried in PRAs not because you believe, you know, plus or
minus that second digit, but it's not unusual to come to a
circumstance where you want to subtract one number from
another, and without two digits, you sort of don't know
where you are.
The other thing is without that rounding the
numbers off, some -- it sometimes makes it difficult to
understand exactly where the number came from. And to a
certain extent, in my view, that second and sometimes even a
third digit are just a way of telling you, well, it's these
two numbers added together. You say, ah, okay, now I
understand how you got that number. So it's an identifier.
COMMISSIONER ROGERS: That's a fair comment.
MR. HOLAHAN: But the idea that we don't express
--
. 91
CHAIRMAN JACKSON: Okay. I think we've said
enough.
Commissioner Dicus?
COMMISSIONER DICUS: No questions.
CHAIRMAN JACKSON: Commissioner Diaz?
COMMISSIONER DIAZ: Let's see. There's a quote
from a philosopher that says the road to knowledge always
crisscrosses the unknown, and I can't remember who wrote
that, but it's a very old thing. I think the staff has made
a very deliberate attempt this week to provide us with
information, what they know, and also what they don't know,
and I think that's very important and I want to thank you
for that.
I think everybody realizes and keeps commenting
that all these issues are linked together. I think we need
to recognize the fact that, before my time, at least, the
Commission has recognized the importance of this issue, has
accelerated the process to bring them to some closure, and I
think the staff has captured that guidance and that drive.
Saying that, I would like to say that I think it's
important that in every one of these projects, we come to
some closure, even if it's step-wise and even if it
recognizes that it is, you know, a step, because if not, you
know, we can go on and continue forever and never, never
stop. So I think it's important that we --
. 92
CHAIRMAN JACKSON: That's right.
COMMISSIONER DIAZ: -- close the issues.
I have one comment which I don't know whether it's
appropriate or not. When we put this database in the
Internet and so forth and the fact that the information has
not been updated, it might not be a bad idea to suggest to
the licensees that on a voluntary basis, they can access
their own information and update it. It might be a very,
very simple way of getting additional information. You
know, we'll protect our own database, but if they can
actually go in there, they -- probably people that love to
cruise the web might be able to give us some information on
that.
The last point, I want to express some concerns,
and this has been something that has been mounting, is on
the capabilities of the regions to practice these issues,
and I think that we must realize that no matter what
technique we develop, unless they are, you know, implemented
at the region, we're just really a lot of bang -- a lot of
noise and no bang. So I would like to stress that we need
to move almost in parallel.
CHAIRMAN JACKSON: I agree with that completely.
COMMISSIONER DIAZ: Thank you.
CHAIRMAN JACKSON: Commissioner McGaffigan.
COMMISSIONER McGAFFIGAN: I have expressed my
. 93
uncertainties about the uncertainties often enough. I think
I'll just pass.
CHAIRMAN JACKSON: Thank you.
COMMISSIONER McGAFFIGAN: They have a very
difficult job ahead of them.
CHAIRMAN JACKSON: Exactly.
And I would like to thank you very much for a very
informative and candid briefing on the insight program, and
I think you've heard all of us commending you for the
progress you've made.
I'm pleased that you've identified a number of
follow-up activities related to the IPE program bearing in
mind what Commissioner Diaz had to say about coming to
closure on step-wise basis, and I'm particularly interested
in the use of IPE results to assess the regulatory
effectiveness of major safety issue resolution or at least
what the crossing has been, and just to get a readout and
understand where we are.
I think it's very important, the issue of
prioritization with respect to inspection activities,
including the training of the inspectors and the development
of the other regional capabilities on an expedited basis.
You mentioned having the senior reactor analysts and sort of
some wrinkles with getting them out, but if there's a need
-- if there's a way to accelerate and get a bigger bench to
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start with, then we need to think about that.
You mentioned the station blackout rule today and
we talked about some others, and I believe you're also
considering the regulatory effectiveness of the ATWS rule.
I would expect that the regulatory effectiveness
organization, including the Office of Research, will be
involved in these activities?
MR. THADANI: We will be in all the activities
we've been talking about.
CHAIRMAN JACKSON: And from the standpoint of
regulatory effectiveness, I would encourage your continued
focus on, you know, this particular aspect of the use of IPE
insights as we transition into the risk informed framework
and in terms of what you might contemplate. I think it
would be appropriate for you to inform the Commission of
your scope and schedule of activities.
Then the last area I wanted to look -- and it does
relate again to the closure and it overlaps with the others.
You know, it's one thing to talk about using the IPE
insights in a regulatory effectiveness framework; another is
what -- a separate is what I'd call regulatory creep in the
use of IPEs.
Now, I'm interested in this tracking of all the
regulatory uses we've made of IPE insights and how we intend
to move from that to the risk informed framework based on
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the newer guidance documents, because you have heard the
admonishment from Commissioner Rogers repeatedly that the
IPEs have a certain purpose.
The PRAs were a tool for achieving that purpose,
but now we've laid out some guidance relative to PRAS and
their regulatory use, and we want to ensure that that's
where we're going and that we don't misuse what we started
with, but what we do is referenced even as we look at what
else we can glean.
So unless there are any further comments, we're
adjourned.
[Whereupon, at 4:20 p.m., the briefing was
adjourned.]
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