United States Nuclear Regulatory Commission - Protecting People and the Environment

Resolution of Generic Safety Issue 93, "Steam Binding of Auxiliary Feedwater Pumps" (Generic Letter No. 88-03)

                                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). 



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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. 
.

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
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