Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No : 6835
IN 85-46
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
June 10, 1985
Information Notice No. 85-46: CLARIFICATION OF SEVERAL ASPECTS OF
REMOVABLE RADIOACTIVE SURFACE
CONTAMINATION LIMITS FOR TRANSPORT
PACKAGES
Addressees:
All nuclear power reactor facilities holding an operating license (OL).
Purpose:
This Information notice is provided to clarify the application of the
U. S. Department of Transportation (DOT) requirements pertaining to the
control and monitoring of removable radioactive surface contamination on
packages and transport vehicles. It is expected that recipients will
review this information for applicability to their transportation
activities, and consider actions, if appropriate, to preclude any
problems from arising due to inappropriate applications of the DOT
requirements. However, suggestions contained in this notice do not
constitute NRC requirements; therefore, no specific action or written
response is required. Specific clarification and guidance is provided in
the Attachments on:
1. Averaging of Wipe Samples
2. Use of Higher Efficiency Wipe Sampling Methods
3. "Wrapping" of Packages
4. Exclusive-use Vehicle Surveys for Surface Contamination
Background:
The recent resumption of transportation of commercial power reactor spent
fuel in the U.S. has focused renewed attention on the chronic problem of
cask "weeping." This is a phenomena whereby certain casks, after their
removal from underwater storage basins (pools) and decontamination,
subsequently exhibit an increase in the level of removable radioactive
surface contamination during and after transport. This increase is
believed to be the result of a "weeping" or "sweating" of previously
entrapped activity within surface pores, fissures, etc. Its occurrence
and magnitude appear to be dependent on such variables as cleanup
methods, surface porosity, types of detergents used, surface treatment
history, duration of and temperature during transport, and the period of
time between completion of transportation and performance of a
contamination survey. Although the levels of contamination which have
been observed in cask "Weeping" episodes do not present a significant
health and safety problem, the levels have been
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IN 85-46
June 10, 1985
Page 2 of 3
technically above the regulatory limits, particularly when no further
consideration is given to determining the wiping efficiency more precisely
than the ten percent efficiency that is assumed within the regulatory
limit. Recent changes to DOT regulations as promulgated in Docket HM-169
(48 FR 10218, March 10, 1983, and 48 FR 31214, July 7, 1983) have also
raised a question because of an apparent unintended revision in the
regulatory language relating to averaging of wipe samples.
Notwithstanding the guidance in this notice, shippers of radioactive
packages, particularly spent fuel casks, are reminded of the continuing
need for improving cask decontamination methods and spent fuel pool
techniques, so as to maintain removable radioactive surface contamination
levels as low as practicable.
Current Regulatory Requirements:
The DOT regulations in 49 CFR 173.443 prescribe limits for control of
removable (nonfixed) radioactive contamination. The level of such
contamination on the external surfaces of each transport package offered
for shipment must be kept as low as practicable. Determination of the
nonfixed contamination may be made by wiping (e.g., "smears") an area of
300 cm2 of the surface concerned with an absorbent material, using
moderate pressure, and measuring the activity on the wiping material.
Sufficient wipe samples should be taken in the most appropriate locations
so as to yield a representative assessment of the nonfixed contamination
levels. The limits of 173.443, Table 10, are restated below:
TABLE- 10 - REMOVABLE EXTERNAL
RADIOACTIVE CONTAMINATION - WIPE LIMITS
Maximum
Contaminant Permissible limits
uCi /cm2 dpm/cm2
Beta-gamma emitting radionuclides;
all radionuclides with half-lives
less than ten days; natural uranium;
natural thorium, uranium-235; uranium-238;
thorium-232; thorium-228
and thorium-230 when contained in
ores or physical concentrates 10-5 22
All other alpha emitting radionuclides 10-6 2. 2
The above limits apply to packages transported as nonexclusive use, e.g.,
mixed freight. For packages shipped as exclusive-use by rail or public
highway, the provisions of 173.443(b) provide that the removable
(nonfixed) radioactive surface contamination at any lime during transport
may not exceed 10 times the limits stated above. At the beginning of
transport, however, the levels may not exceed those stated above.
Further, pursuant to 173.443(c), any transport
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IN 85-46
June 10, 1985
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vehicle in which packages are transported within the "factor of 10" higher
values, e.g., above the Table 10 limits, must be surveyed with appropriate
radiation detection instruments after each use and shall not be returned
to service until the radiation dose rate is below 0 5 mrem/hr and the
removable contamination is below the limits stated in the above table.
(An exception to this vehicle survey requirement is provided by
173.443(d) for closed transport vehicles (highway) which are dedicated
solely to the transport of radioactive materials packages and are
appropriately marked on the exterior of the vehicle. Also, in such cases
the removable surface contamination on packages within such vehicles may
be at the "factor of 10" limits at the start of transport).
No specific action or written response to this information notice is
required. If you have any questions on this matter, please contact the
appropriate NRC Regional office or the technical contact listed below.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Contact: A. W. Grella, IE
(301) 492-7746
Attachments:
1. Averaging of Wipe Samples
2. Use of Higher Efficiency Wipe Samples
3. "Wrapping" of Packages (Casks)
4. Exclusive-use Vehicle Surveys for Surface Contamination
5. List of Recently Issued IE Information Notices
.
Attachment 1
IN 85-46
June 10, 1985
AVERAGING OF WIPE SAMPLES
The DOT regulations currently state in 173.443(a) that "... the amount of
radioactivity measured on any single wiping material when averaged over
the surface wiped .. " shall not exceed the Table 10 values. Prior to the
regulatory amendments by DOT in 1983 (see Docket HM-169, 48 FR 10238,
March 10, 1983), formerly applicable 173.397(a) provided that wipe
samples could be "...averaged over any area of 300 square centimeters of
any part of the package surface." A February 21, 1984 query was made by
NRC to DOT to clarify this matter. It read as follows:
The language of 173.443(a) has been modified somewhat from that contained
in the previous 173 397(a). The new language no longer specifically
addresses averaging of multiple wipe samples within any given 300 cm2
area of a package surface. We understand that it was not DOT's intention
to disallow such averaging and further that DOT will consider processing
a future rule change to restore such a provision to 173.443. A suggested
text for such a modification is enclosed. In the interim, until the text
has been formally modified, we will continue to consider that averaging
of multiple wipe samples over any 300 cm2 area of a package surface is an
acceptable practice.
In their March 19, 1984, reply to NRC the DOT stated:
It was not our intent to disallow averaging of wipe samplings over a 300
cm2 area. Consequently, we believe this is an acceptable practice and
will take the necessary action to clarify this in 173.443(a)....
.
Attachment 2
IN 85-46
June 10, 1985
Page 1 of 2
USE OF HIGHER EFFICIENCY WIPE SAMPLES
As is stated in 173.443(a): "Other methods of assessment of equal or
greater efficiency may be used. When other methods are used, the
detection efficiency of the method used shall be taken into account and
in no case shall the nonfixed contamination on the external surfaces of
the package exceed ten times the limits listed in Table 10." NRC also
queried DOT on this matter, as follows:
We understand that DOT considers that the reference in 173.443(a) stating
that `other methods of assessment of equal or greater efficiency may be
used,' may include other wipe sampling methods wherein the efficiency has
actually been demonstrated to be greater than 10 percent. Therefore, in
effect, the wipe sample limits stated in 173.443(a) and (b) and Table 10
therein, are limits "by default," which do not take advantage of
utilizing an efficiency which has been demonstrated to be greater than 10
percent. In our evaluations of licensees' package surveys, we therefore
plan to accept assessments based on efficiencies which have been
appropriately demonstrated to have a higher than 10 percent efficiency.
The reply by DOT on the usage of higher efficiency wipe samples was as
follows:
It is our interpretation of this section that wiping methods with a
demonstrated efficiency greater than 10 percent may take this greater
efficiency into account. As you point out, the higher efficiency must be
documented and in no case may the removable levels exceed 10 times the
values in Table 10.
It should be understood that where the term "detection efficiency" is
used, it refers to the efficiency of alternate methods for quantifying
the amount of removable contamination on a package surface. It does not
refer to the laboratory term relating to instrument effectiveness for
counting analyses.
An additional clarification also was received from DOT relative to use of
contamination assessment techniques with greater than 10% efficiencies in
exclusive-use vs nonexclusive-use shipments. It stated that "the provision
for using higher efficiency techniques, described in 49 CFR 173.443(a)
may also be used when operations are being performed in accordance with
173.443(b)."
An acceptable method of demonstrating wipe (smear) efficiency is
repetitive wiping of a portion of the package surface. The demonstrated
wipe efficiency is the ratio of the initial smear activity to the
summation of activity on all the wipes of the designated portion of the
package surface. For the purpose of this calculation, one can assume all
activity is removed when two consecutive wipes show less than 10% of the
activity of the initial wipe. Because of variations in package surfaces
and contamination characteristics, care should be
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Attachment 2
IN 85-46
June 10, 1985
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taken to ensure that the demonstrated wipe efficiency is representative of
the wipes to which it is applied. This will normally require delaying
package decontamination until after conduct of wipe efficiency
determinations if an efficiency greater than 10% is used. In no case,
however, may the removable contamination levels exceed ten times the
Table 10 limits for packages in exclusive-use shipments when no
consideration is given to a demonstrated higher wiping efficiency. Upon
such an appropriate demonstration, however, removable contamination
limits may not exceed 100 times the Table 10 limits, as would be the case
for a wiping method demonstrated to have been 100% efficient.
In general, licensees may only utilize demonstrations of high smear
collection efficiencies which have been determined by smear results taken
on the same cask for which the initial smears (using the assumed 10%
efficiency) indicated the regulatory limit was exceeded. Licensees will
not be allowed to use the generic collection efficiencies obtained on one
specific cask for other future cask shipments.
.
Attachment 3
IN 85-46
June 10, 1985
"WRAPPING" OF PACKAGES (CASKS)
The question of "wrapping" the exterior of transport packages has been
raised on several occasions, particularly in instances where "weeping" of
contamination has occurred on casks that have been immersed in spent fuel
storage pools prior to transport. DOT also was queried on this matter by
NRC as follows:
The issue of whether exterior "wrapping" of casks can be used to achieve
compliance with removable contamination limits has been raised on a number
of occasions. Our position on this, with which I understand you also
concur, is as follows:
x The addition of "wrapping" to an NRC-certified package would not be
permissible without_obtaining prior authorization of the modification in
the applicable NRC certificate. In proposing such a provision, an
applicant's safety analysis obviously would have to address heat
retention since the contents are a heat source.
x The "wrapping" of a non-NRC certified package would not relieve the
shipper from compliance with the removable contamination limits
applicable to the exterior surface of the unwrapped package unless the
wrapping constituted an integral part of a DOT Specification 7A, Type A,
package design. In such cases, the shipper's documented package safety
evaluation would need to address whether the wrapping would maintain its
closure integrity during the normal conditions of transport.
The reply to NRC by DOT on this matter read as follows:
For both NRC-certified and non-NRC-certified packages, any wrapping must
be addressed in the package design evaluation. For NRC certified packages
this would include specific mention in the certificate of compliance. For
DOT Specification 7A, Type A, packages, the shipper's package safety
evaluation would have to document the ability of the wrapping to
successfully pass the Type A tests.
.
Attachment 4
IN 85-46
June 10, 1985
EXCLUSIVE-USE VEHICLE SURVEYS FOR SURFACE CONTAMINATION
The exact requirements of 173.443 are sometimes misunderstood as they
relate to quantitative limits on the vehicle surface during the survey
required by 173.443(c). For this purpose, the vehicle surface is meant to
be those surfaces wherein or on which packages are stowed during
transport. That paragraph does not actually set forth any quantitative
limit on the surface of the vehicle itself during the survey which is
performed to return the vehicle to service. The important subtlety
therein is that the quantified limit of 173.443(b) applies to the
packages in the vehicle. The "bottom line" of 173.443(b) and (c),
considered collectively, is as follows:
x The packages within an exclusive-use vehicle may have up to 22,000
d/m/100 cm2 during and at the completion of transport but must be limited
to 2,200 d/m/100 Cm2 at the start of transport, unless the vehicle is
dedicated to radioactive materials service only, and so marked, pursuant
to 173.443(d), in which case the 22,000 d/m/100 cm2 limit applies at the
start of transport.
x 173.443(c) requires a survey of an exclusive-use vehicle (and also,
presumably the dedicated vehicles) after transport of packages that
indicate removable contamination above the Table 10 limits, but within
the "factor of ten" higher limit of 22,000 d/m/100 cm2.
x 173.443(c) does not address quantitative limits on the surface of the
vehicle during the survey, however, the vehicle may not be released for
other service until the 2,200 d/m/100 cm2 and 0.5 mrem/hr limits are met.
x Noncompliance with 173.443(c) would therefore exist if the survey to
return a vehicle to service was not performed, and/or the contamination
or radiation dose rate on the vehicle exceeded the stated limits upon its
release for other service.