ML16341C342
| ML16341C342 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 11/06/1978 |
| From: | Buhl A NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML16340A293 | List: |
| References | |
| NUDOCS 7812010019 | |
| Download: ML16341C342 (4) | |
Text
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ENCLOSURE NO.
3 UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 NOV 6
1978 MBD1MfIXMFOR:
John F. Stolz, Chief Light Water Reactor Branch No. 1 Division of Project Yanagenent Office of Nuclear Reactor Regulation FHM:
Anthony R. Buhl, Director Probabilistic Analysis Staff Office of Nuclear Regulatory Research SUBJECT LVAUJATION OF DIM3XD CANYON ANALYSIS OF RISK
'lQ THE PUBLIC FKM SEISMIC EVEN'ZS By memorandum dated September 8, 1978, we transmitted our evaluation of Amendment 52 to the Diablo Canyon license application for your use and information.
As requested by Yir. Denton, we have reviewed our evaluation in light of the ccmIrIents of the Risk Assessrrent Review Group (NURZG/CR-0400).
The basic conclusions of our evaluation of Diablo Canyon remain unchanged as a result of this reexamination, (1)
. i.e., the estimates for the conditional probability of core melting
'nd of the large release presented by the applicant are somewhat conservative, (2) use of the applicant's estimate of seismic frequency leads to an estimate of the probability of core melting given a seismic event of 9 x 10
/reactor-year, (3) use of the staff estimates of earthquake probabilities would increase this by a factor if 4-6, and (4) the. assumptions made in consequence modeling could understate the
~ ccapldmentary curIrulative distribution functions (ccdfs) for doses at various locations by a factor of about five.
Thus, when combined, the applicant's ccdfs could increase by a factor of 20-30 over that predicted by the applicant, if the staff seismic frequency values are used.
The following clarifications should be added to our previous evaluation:
1.
- p. 5, delete the last sentence of the SurrImary and substitute the follcI~g:
"Because of the assumptions regarding seismically-induced loss of a.c. pcwer referenced
- above, we consider the estimates for the conditional probability of core melting and for the conditional probability of a large release given a seismic acceleration to be somewhat conservative, but we cannot quantify the degree of conservatism involved.
We have not attested to quantify the uncm<ainties associated with the estimates of earthquake probabilities but recognize they may be large.
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John F. Stolz Thus, the uncertainties associated with the overall estimates presented above for the likelihood of core melting and for the likelihood of large releases may also be large."
2.
- p. 8, add after last, sentence in the Sugary:
As previously noted, we recognize that there may be large uncertainties associated with the estimate of the likelihood of seismic accelerations.
Because of these uncertainties, when coupled with the uncertainties inherent in the various aspects of the'onsecp.ence calculations, there may be considerable uncertainty associated with the results.
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/'.(Lie.'nthony R. Bu., Director Probabilistic Analysis"Staf Office of Nuclear Regulatory Research