ML20211K505
| ML20211K505 | |
| Person / Time | |
|---|---|
| Issue date: | 11/24/1986 |
| From: | Speis T Office of Nuclear Reactor Regulation |
| To: | Bernero R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20209E138 | List: |
| References | |
| FOIA-87-10 NUDOCS 8612050080 | |
| Download: ML20211K505 (2) | |
Text
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%' p t.no UNITED STATES
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555
%*****/ November 24, 1986 MEMORANDUM FOR: Robert M. Bernero, Director Division of BWR Licensing Office of Nuclear Reactor Regulation FROM: Themis P. Speis, Director j
Division of Safety Review and Oversight Office of Nuclear Reactor Regulation
SUBJECT:
IDCOR EVALUATION OF BWR ACCIDENT MITIGATION CAPABILITIES In response to your request of September 22, 1986, we have reviewed the IDCOR report entitled, " Evaluation Of BWR Accident Mitigation Capability Relative To Proposed NRC Changes." In general, we find that much of the disagreement between NRC and IDCOR on the phenomenology of core melt accidents is reflected in the discussion and conclusions of this report. The IDCOR report underestimates the risks associated with the Mark I containments and assigns unduly low benefit to some of the proposed improvements. Nevertheless, IDCOR
\ has taken a positive engineering approach to the question of accident
) mitigation and has identified some practical problems and some competing .
risks. It is clear, however, that none of these problems is insurmountable and that generic or plant specific engineering solutions can be developed by the BWR owners group.
Our specific coninents relate to the summary evaluations discussed in section 7 of the report and depicted in table 7.1-1, 7.2-1 and 7.3-1.
For Mark I containments, IDCOR places high emahasis on debris bed coolability, and asserts that the primary path should be t1 rough RPV injection. From an overall safety perspective, injection to the RPV is preferred because the first objective'of accident response should be to prevent core damage.
However, from the perspective of accident mitigation, we believe that drywell sprays are the preferred alternative provided the flow is sufficient to ensure fission product scrubbing, depressurization, and cooling of the containment shell for all scenarios including station blackout.
The IDCOR evaluation of venting for mitigation of core melt accidents (includingATWS)islimited. A more comprehensive discussion of the considerations for wetwell venting is presented in the draft BNL Guidelines and Criteria for Mark I plants. The onus should be on the owners group and the individual plants to engineer venting schemes which meet the requirements of drywell depressurization and fission product scrubbing, without producing the negative side effects described in the IDCOR report.
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R. Bernero November 24, 1986 The IDCOR discussion of drywell barriers does not support their assignment of
" low" safety benefit. Any plan for improving containments should address all credible failure modes, including drywell meltthrough for the Mark Is and downcomer meltthrough for the Mark IIs.
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Themis P. Spets, r Division of Safety Review and Oversight Office of Nuclear Reactor Regulation cc: J. Murphy, RES W. Houston G. Lainas L. Hulman
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