ML20038C621
| ML20038C621 | |
| Person / Time | |
|---|---|
| Issue date: | 09/23/1981 |
| From: | Wu T Advisory Committee on Reactor Safeguards |
| To: | Plesset M Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1377, NUDOCS 8112110296 | |
| Download: ML20038C621 (2) | |
Text
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NOV2 0198% r3 To:
M. S. Plesset, ACRS va M 7 "
nata-9-23-81 %
From:
T. Y. Wu b,
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Subject:
ACRS ECCS Subcommittee meenn -
gust 40, 1981 - Monterey, Ca.
1.
GE Proposal for Appendix K Rule Change GE's proposal for decay-heat rule change and modifications to their ECCS EM (Evaluation Model) is based on their belief that there is considerable (over 10000F) margin in the calculation of PCT. It has been clarified by GE and NRC Staff that the new BE (best estimate) decay heat data can provide relief to burdens imposed by excessive Appendix K conservatism.
Of the two approaches by procedural change and technical change, it seems that while an exemption (to the regulation) could bring about an early relief, the issue must be settled on a sound technical basis in view of the requirement of 10 CFR 50.12, including the clause that "the exemption --- will not endanger life or property -- ".
As the chief goal is to increase effectiveness and to alleviate unduly excessive operational cost of labor and material, such changes should be considered, to be done not by piecemeel, but by an unified integral approach.
In order to justify the rule change, much additional new information must be considered and much preparatory work needs to be done, they include qualification of heat transfer coefficient in various mode of film boiling, steam cooling and phase transition, fuel rupture, etc. Investigation of the impact due to variations of these factors on the safety margin must be thoroughly pursued for not only SB but all LOCA transient thermohydraulics.
I would like to recommend that the Staff's endorsement of technical accept-ability of new decay heat data be accepted and adopted as a ground for granting a temporary exemption until a rule change study can be accomplished.
It seems quite appropriate that GE be requested to provide a report on impact of its proposed revisions on overall conservatism and operational cost savings.
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2.
Concerning Pump Trip in a SB LOCA The NRC development of a requirement for early main coolant pump trip in the event of a SB LOCA has been aided by the tests carried out in Semiscale and LOFT with pumps on and off. While the test results appear to support i
early pump trip, it is only after simulated SB flows were computed using the RELAP-5 and other appropriate codes did the principal mechanism underlying SB LOCA events become sufficiently clarified. With pumps on and off, the numerical results exhibit. correlations between variation of fluid density up-stream of break, degrec' of subcooling, depletion of coolant, and their effects on the discharge rate of break flow. In spite of these advances, there remain, probably for some time, such uncertainties in the event of a SB LOCA as the l
break location and size, break orientation, local flow stratification, two-phase I
jet flow through break, etc.
Even with such lack of important information f
reasonably overcome, it is necessary to upgrade at least the local handling of the break flow calcelation in the t ode.
a Further code verification versus l
Semiscale and LOFT test data would again require studies of similar and 0112110296 810923 PDR ACRS CT-1377 PDR 19
2 dissimilar features of the two facilities. For instance, a major difference between the two has been ascribed to the dissimilar pump characteristics in prolonged two-phase operation.
t It seems that the aforementioned factors ought to be considered in making-the decision whether the pump trip should be manual or automatic. The result of such a definitive study not being in hand, I am tempted to suggest that an alternative be investigated to have a provision of automatic trip which can be superseded or overruled by manual operation.
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