Seismic Hazard Position

DOE-STD-1024-92

analysis is not available then the NUREG-CR/0098 median

spectral shape should be used.

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.

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.