ML20003C769
| ML20003C769 | |
| Person / Time | |
|---|---|
| Issue date: | 12/19/1980 |
| From: | Minogue R NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Ahearne J NRC COMMISSION (OCM) |
| Shared Package | |
| ML20003C742 | List: |
| References | |
| REF-10CFR9.7, RULE-PRM-50-29, TASK-OS, TASK-SG-029-3, TASK-SG-29-3 NUDOCS 8103180236 | |
| Download: ML20003C769 (2) | |
Text
UKLdf rete 7 A CRETARIAT RECORD COPY
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DEC 1 9 152C MEMORANDUM FOR:
Chairman John Ahearne THRU:
William J. Dircks RaeD William J. Dggig' Executive Director for Operations' FROM:
Robert B. Minogue, Director Office of Nuclear Regulatory Research
SUBJECT:
ATWS CALCULATIONS On November 10, 1980, you requested that the Systems and Reliability Research Division (SARR) review and coment on the ATWS calculations presented to the Comission by J. Lellouche of EPRI and W. Minners of NRR.
We comited to do so by December 12. A sumary of their findings follows:
The EPRI calculations of Reactor Protection System unavailability are incomplete and over-optimistic.
The NRR treatment of the num' car of tests that.should be credited in such calculations is a better est' mate.
Both EPRI and NRR treatments of the " rectification" of the Kahl failure are legitimate applications of statistical methods.
l EPRI has a valid point in suggesting that the staff is unnecessarily conservative in its treatment of the oppor-tunities to fix or learn from precursor events.
Both EPRI and NRR analyses are misleading in the levels of confidence they attribute to their probability estimates.
Though statistically correct, such measures of uncertainty ignore inaccuracies in the implicit assumptions within the model.
These may be quite large.
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Chairman John Ahearne.
EPRI is not correct,.in asserting that the addition of rrore pressurizer safety values in PWRs would necessarily increase public risk.
A more detailed presentation o.f the SARR review of the ATHS calculations is attached.
- criginsi signed Bf Robert B. Minogue, Directo.r Office of Huclear Regulatory Research
Enclosure:
As stated cc:
H. Danton.
Con.missioner Hendrie T. Murley Comissioner Gilinsky D. Ross Comissioner Bradford R. Bernero
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