ML20207Q193
| ML20207Q193 | |
| Person / Time | |
|---|---|
| Issue date: | 12/04/1986 |
| From: | Jensen W Office of Nuclear Reactor Regulation |
| To: | Berlinger C Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8701230186 | |
| Download: ML20207Q193 (5) | |
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UNITED STATES J
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- j WASHING TON, D. C. 20555 DEC 0 41986 PEMORANDUM FOR:
Carl H. Berlinger, Chief Reactor Systems Branch Division of PWR Licensing-A THRU:
Richard Lobel, Section Leader Reactor Systems Branch Division of PWR Licensing-A FROM:
Walton L. Jensen Senior Nuclear Engineer Reactor Systems Branch Division of PWR Licensing-A SUPJECT:
MEETING WITH WESTINGHOUSE OWNERS GROUP, LOCA IN MODE 4 On November 6,1986, members of the NRC staff met with the Westinghouse Owners Group Analysis Subcomittee. The list of attendees is attached. The purpose of the meeting was to address a concern raised by Westinghouse that RHR pump damage might occur as a result of a Mode 4 LOCA.
In Mode 4, hot shutdown, the RHR pumps are aligned to take suction from one or two of the reactor system hot legs for decay heat removal and plant cooldown.
If a LOCA occurred with the RHR pumps connected to the hot legs the pumps might be damaged from loss of suction pressure. Westinghouse recommended that operators trip the RHR pumps to prevent damage and manually align the pumps to take suction from the RWST to provide safety iniection. Westinghouse estimated that as little as 3 s
minutes might be available to trip the RHR pumps for small breaks and less time for large breaks. Westinghouse informed the staff of the LOCA in Mode A issue in a letter dated June 13, 1986. The staff pursued resolution of the issue on the Vogtle docket where it is currently open.
The Westinghouse Owners proposed a three point program to resolve the issue generically.
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1.
Find the maximum credible break size using leak-before-break technology.
The owners believe that leak-before-break technology can show that pipe sizes larger than 6 inches (5.187 inches ID) will not break catastrophically.
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Analyze LOCA in Mode 4 with the maximum credible break size to find the time for operator action to trip the RHR pumps before NPSH is lost and 1
align them to the RWST to prevent core damage. The time to RHR pump damage once NPSH is lost will not be evaluated by the owners nor will this time be credited for operator action.
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3.
Evaluate and propose solutions to the licensing aspects of the problem.
The staff provided comments concerning the legal, mechanical and thermal hydraulic aspects of the owners' proposals. The staff lawyer stated tet before large pipe breaks could be excluded that an exemption would have to be-obtained from the reoutrements of 10CFR50.46 that a full break spectrum be considered.
It was noted that although leak-before-break arguments have been accepted for obtaining relief from the dynamic effects of pipe break reouired by GDC 4, the Commission's policy has been to exclude ECCS performance analyses from these considerations. Exclusion of double ended break sizes from the ECCS analysis in Mode 4 would therefore require a change in staff policy as well as an exemption from 10CFR50.46.
Representatives of the Engineering Branch expressed general agreement that engineering arguments could be developed to demonstrate that large pipino breaks are not credible based on leak-before-break arguments, however this would have to be done individually for each plant or at least each plant would have to be demonstrated to be covered by a generic analysis. The owners did n.ot propose to evaluate the plants individually but said they would consider the staff's request.
'Since complete resolution of ths'LOCA in Mode 4 issue may require a year or more, the staff suggested that an interim solution might be developed. The interim solution would involve instructions to the operators and administrative controls to ensure that necessary equipment is operable. Several possibilities were discussed including restricting operation when both RHR pumps are taking suction from the hot legs so that both pumps could not be damaged in the event of a LOCA.
If the operator were to trip the RHR pumps imnediately following a LOCA, decay heat removal by the RHR trains would cease.
For small breaks of the order of 3 inches diameter the reactor system would repressurize such that the operable ECCS pumps might not be able to inject sufficient ficw to maintain core cooling. Part of the interim solution could be to ensure that additional ECCS pumps ere available or that additional decay heat removal capability is available using the steam generators. The staff expressed concern that actuation of additional ECCS pumps might cause Appendix G cold overpressure limits to be exceeded.
Automatic -ECCS actuation on high containment pressure is not normally reouf red in Pode 4 This protection might be beneficial for large break LOCAs but would not be actuated for small break sizes.
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The Westinghouse owners agreed to evaluate the staff comments on the long range program as well as on the benefit of an interim solution and proposed to have further discussions and proposals for staff consideration in approximately one month.
Walton Jensen, Senior Nuclear Engineer Reactor Systems Branch Division of PWR Licensing-A cc:
C. Rossi J. Scinto P. Boehnert J. Wilson J. Guillen R. Woodruff M. Miller A. Sp3no S. Lee T. Sullivan B. Elliott C. Thomas W. Hodges W. Minners DISTRIBUTION:
Central File RSB RDG CBerlinger RLobel WJensen Nk R(R.
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-A RSB:PWR-A WJens n:sl RLobel 1?/2./86 12/$86
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