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| ![]() DOE-STD-1024-92
analysis is not available then the NUREG-CR/0098 median
spectral shape should be used.
B:
For those sites that have only the LLNL or EPRI probabilistic
seismic hazard results the recommendation is to use the above
factors (in A3 above) on an adjusted median curve as described
below. The factor selected to adjust the median is 1.2 (i.e., LLNL
median result divided by 1.2) if only LLNL results are available
with LLNL-AE5). This factor represents the difference between
the LLNL and EPRI median hazard curves at both reactor sites
and DOE sites. For sites that have only LLNL results without
LLNL-AE5 these median results should be used directly. For a
site that would have only EPRI results available (none are known
to currently exist) it is recommended that LLNL results be
quantified for that site. If this cannot be accomplished, the EPRI
median should be multiplied by 1.2 In following the Standard,
however, all sites which have both results must use the position
developed using both results.
C:
The seismic hazard position does not explicitly apply to Probabilistic
Risk Assessment (PRA) studies. Probabilistic Risk Assessments
being completed should evaluate both LLNL and EPRI hazard
curves individually to ensure that there is an adequate seismic
understanding of the dominant seismic sequences. Thus, these
results should be used in a relative sense. The absolute seismic
PRA numbers should not be relied on considering the issues
associated with the individual EPRI and LLNL hazard curves.
The advantage of the above approach is that the most stable hazard
estimate is used while recognizing the existing uncertainty. The difficulty
of this approach relates to how the correction factor is estimated. The
correction factor was developed by reviewing the LLNL and EPRI results
(fractiles ranging from the 15 percent to 85 percent) for the commercial
nuclear power plants in the Eastern United States. This recommendation
is thought to represent a reasonable interim solution, and was developed
to address the limitations in existing hazard analyses discussed below.
The specific value for the correction factor is thought to be conservative in
that future work will demonstrate that the mean hazard curves are lower
than values recommended by this position. The discussion below also
summarizes the development of this factor.
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