Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON. D. C. 20555
February 17, 1988
TO ALL LICENSEES, APPLICANTS FOR OPERATING LICENSES, AND HOLDERS OF
CONSTRUCTION PERMITS FOR PRESSURIZED WATER REACTORS
Gentlemen:
SUBJECT: RESOLUTION OF GENERIC SAFETY ISSUE 93, "STEAM BINDING OF AUXILIARY
FEEDWATER PUMPS" (GENERIC LETTER 88-03)
This generic letter is being issued:
(1) to inform you of the staff's resolution of the subject generic
safety issue, and
(2) to request that you continue to implement, as a minimum, the
monitoring and corrective procedures previously identified for
interim resolution of this issue in IE Bulletin 85-01, "Steam
Binding of Auxiliary Feedwater Pumps," dated October 29, 1985.
(A copy of this bulletin is attached.)
The issue concerns the potential disabling of auxiliary feedwater (AFW)
pumps by steam binding that is caused by backleakage of main feedwater (MFW)
past the isolation check valves between the AFW and MFW systems. The issue
is significant because most AFW systems are potentially vulnerable to common
mode failure of the redundant AFW pumps as a result of steam binding. This
vulnerability is inherent to the piping configurations used, which allow
redundant trains of AFW to be cross-connected via common headers on the
suction and discharge sides of the pumps.
To reduce the probability of AFW pump failure as a consequence of steam
binding if backleakage does occur, IE Bulletin 85-01 requested that certain
licensees and construction permit holders implement procedures both for
monitoring the AFW piping temperatures for indication of possible
backleakage and for restoring the pumps to operable status if steam binding
were to occur. The bulletin was not issued to all holders of operating
licenses and construction permits for pressurized water reactors because the
staff had determined that a number of them had already taken actions that
would minimize the occurrence of the AFW pump steam binding problem at their
plants. The bulletin recommended a monitoring frequency of once a shift,
compared with the previously recommended frequency of once a month. This
increased frequency reduced the likelihood of pump unavailability because of
steam binding by a factor of 90 (3 shifts/day x 30 days/month).
8802180267
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Multiple Addressees - 2 - FEB 17 1988
As part of its efforts toward a final generic resolution of this issue, the
staff surveyed the backleakage experience in operating plants following the
implementation of monitoring procedures. Although the number of backleakage
events varied from an average of less than one per reactor year at a large
majority of plants to more than 100 per reactor year at others, none of the
backleakage events that occurred during the review period appeared, to have
resulted in, the steam binding of an AFW pump. This indicates that the
various monitoring methods employed can be highly effective in preventing
steam binding if backleakage occurs. For the plants with a high backleakage
event rate, the installation of continuous monitoring systems with control
room alarms was instrumental in providing for early warning to the operator
and timely corrective action.
The results of the staff's regulatory analysis indicated that following the
recommendations in Bulletin 85-01 would ensure that the contribution of AFW
pump steam binding to core melt frequency and public risk was sufficiently
low and that there is no need for new recommendations beyond those in IE
Bulletin 85-01.
The staff has concluded that the recommended monitoring actions of IE
Bulletin 85-01 should be continued. However, although the staff has
concluded that the currently assessed risk associated with this issue is
reasonably low, it is still concerned about the generally unsatisfactory
reliability of check valves in operating plants. Plant operators should
continue to be alert to the possible development of malfunctioning check
valves, especially as the plant ages. They should be prepared to increase
the monitoring frequency as needed and to implement appropriate recovery
procedures to ensure that steam binding failure of the AFW pumps does not
occur.
IE Bulletin 85-01 recommended that procedural controls remain in effect (1)
until the completion of hardware modifications to substantially reduce the
likelihood of steam binding, or (2) until it was superseded by action
implemented as a result of resolution of Generic Issue 93. This Generic
letter resolves Generic Issue 93 by perpetuating the recommendations of IE
Bulletin 85-01. In particular, all addressees should:
1. Maintain procedures to monitor fluid conditions within the AFW
system each shift during times when the system is required to be
operable. This monitoring should ensure that fluid temperature at
the AFW pump discharge is maintained at about ambient levels.
2. Maintain procedures for recognizing steam binding and for
restoring the AFW system to operable status, should steam binding
occur.
All addressees are requested to provide a letter of confirmation to the NRC
within 90 days of receipt of this generic letter indicating that the
procedures discussed in this generic letter are in place and will be
maintained. Confirmation by addressees who did not previously receive IE
Bulletin 85-01 is being requested because the staff believes that they would
rely on these procedures as part of the actions to minimize the occurrence
of the AFW pump steam binding problem.
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Multiple Addressees -3- FEB 17 1988
Pursuant to 10 CFR 50.54(f), you are requested to submit under oath or
affirmation the letter of confirmation to the U.S. Nuclear Regulatory
Commission, Document Control Desk, Washington, D.C. 20555, for reproduction
and distribution. This request for information is covered by the Office of
Management and Budget under blanket clearance number 3150-0011, which
expires December 31, 1989. Comment on burden and duplication should be
directed to the Office of Management and Budget, Reports Management, Room
3208, New Executive Office Building, Washington, D.C. 20503.
Although no specific request or requirement is intended, the following
information would be helpful to the NRC in evaluating the cost of this
generic letter:
1. Staff tine to perform the requested confirmation and any needed
followup actions.
2. Staff time to prepare requested documentation.
If there are any questions regarding this matter, please contact the
Regional Administrator of the appropriate NRC regional office or your
project manager in this office.
Sincerely,
Frank J. Miraglia, Associate Director
for Projects
Office of Nuclear Reactor Regulation
Enclosure: IEB 85-01
