ML20195G238
| ML20195G238 | |
| Person / Time | |
|---|---|
| Issue date: | 06/10/1987 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Beckjord E NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML20195G243 | List:
|
| References | |
| FOIA-87-714, TASK-093, TASK-93, TASK-OR IEB-85-001, IEB-85-1, NUDOCS 8706190124 | |
| Download: ML20195G238 (3) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION c
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June 10, 1987 MEMORANDUM FOR:
Eric S. Beckjord, Director Office of Nuclear Regulatory Research FROM:
Thomas E. Murley, Director Office of Nuclear Reactor Regulation
SUBJECT:
RESOLUTION OF GENERIC SAFETY ISSUE 93 "STEAM BINDING OF AUXILIARY FEEDWTER PUMPS" Your memorandum of May 1,1987 proposed resolution to Generic Issue 93 "Steam Binding of Auxiliary Feedwater Pumps".
We concur with the proposed resolution.
We have also revised the generic letter on this subject to delete the paragraph which permitted a relaxation in the check valve backleakage monitoring frequency.
l Given the persistent problems with check valve leakage, particularly as the I
valves degrade with age, we see no reason to deviate from the current check l
valve backleakage monitoring frequency that has been implemented by licensees in response to IE Bulletin 85-01. Thepresentfrecuency.(oncepershift)does not impose a significant burden on the licensees, and acceptably ensures that potential auxiliary feedwater pump steam binding will be detected and corrected in a timely manner.
l We propose this modified generic letter be fontarded as part of the CRGR submittal to close out generic safety issue 93.
{Mi&d mas E. Murley, Di cto Of ice of Nuclear Reactor Regulation
Enclosure:
i As stated cc:
F. Miraglia J. Blaha 1
J. Funches F. Hebdon
Contact:
W. LeFaye l
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ENCLOSURE 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" This letter is to infom you of the staff's resolution of the subject safety issue which concerns the potential disabling of auxiliary feedwater (AFW1 pumps by steam binding caused by backleakage of main feedwater (MFW) past the isolation check valves interfacing the AW and MFW systems. The significance of the issue stems from the potential vulnerability of most AFW systets to comon mode steam binding failure of the redundant AFW pumps, this vulner-ability being inherent in the piping configurations used, which allow for cross connections between trains via comon headers on the suction and discharge sides of the pumps.
To reduce the probability (of pump failure by) steam binding if backleakage does occur. IE Bulletin 85-01 dated October 1985 required those licensees and CP holders, who had not already done so in response to previous NRC and INPO recomendations, to implement procedures both for monitoring the AFW piping temperatures as an indication of possible backleakage and for restoring the pumps to operable status if steam binding were to occur or appeared likely to do so. The Bulletin's recommended monitoring frequency of once per shift, compared with the previous once per month check when the pumps were tested, provided for a factor of about 90 (3 shifts / day x30 days / month) reduction ir.
pump average unavailability due to steam binding.
As a basis for the staff's regulatory analysis of this issue, a limited review was made of the backleakage experience in operating plants since the start of systematic monitoring (about April 1985 for a majority of the plants). The results showed a double-hurped distribution in recard to backleakage, with the dominant majority of plants showing low incidence of backleakage occurrences (a mean of less than one per reactor year) while the remaining plants showed a far higher event rate by a factor of roughly 100. None of the backleakage events during the review period appeared to have resulted in steam binding of i
i an AFW pump, ir.dicating that the various monitoring methods employed can be highly effective in providing for the prevention of steam binding if backleakage occurs. For the plants with a high backleakage event rate, the installation of i
continuous monitoring systems with control room alanns was instrumental in providing for early warning to the operator and timely corrective action.
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2 The results of the regulatory analysis indicated that, within the framework of the existing Bulletin 85-01 requirements, the contribution of AFW pump steam binding to core melt frequency and public risk was sufficiently low to warrant the finding that no new requirements beyond those specified in IE Bulletin 85-01 need be imposed. Although the staff has concluded that the currently assessed risk associated with this issue is reasonably low, it is nevertheless considered irportant in light of the generally unsatisfactory check valve reliability experience obtaired to date in operating plants, that plant operators continue to be alert to the possible development of malfunctioning check valves, especially as the plant ages, and be prepared to increase the monitoring frequency as needed to ensure that steam binding failure of the AFW pumps does not occur.
No written response or specific action is required by this letter; therefore, no clearance from the Office of Management and Budget is required.
If you have any questions on this matter, please contact your project manager.
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