NRC Generic Letter 88-03, Resolution of Generic Safety Issue 93, "Steam Binding of Auxiliary Feedwater Pumps"

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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).


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Addressees

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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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

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