Approach Selected

DOE-STD-1024-92

4.0

APPROACH SELECTED

As part of determining which approach was best to select, DOE

requested that Dr. C. A. Cornell assist in reviewing the existing LLNL and

EPRI results at the 69 commercial nuclear power plant sites (NPP).

Information in the form of hazard curves and hazard curve ratios (ratio of

the 85th percentile to the median, for peak ground acceleration and

several response spectral ordinates) was provided to Dr. Cornell and

DOE by Risk Engineering Inc. under contract to Martin Marietta Energy

Systems, Oak Ridge. This information was reviewed to determine if

there were any consistent trends in the uncertainty estimates within the

individual LLNL and EPRI studies, and to determine what the trends

were between the two studies. Figures 2 and 3 display typical

information provided. These figures show the ratio of 85th percentile to

the median for 10 hertz spectral frequency for the LLNL and EPRI

studies respectively.

Appendix C provides the full set of information on the hazard curve ratios

for the peak ground acceleration and the spectral frequencies of 25, 10,

5, 2.5 and 1 hertz. Several levels of ground motion are also shown on

each figure. Figures C1 to C6 display the geometric mean of the ratio

between the 85th percentile and the median for the EPRI results and the

LLNL results with and without LLNL-AE5. Figures C7 through C24

display the entire set of reactor data and the geometric mean, 15th and

85th percentiles of the data. As discussed below, the above data can be

used to derive a pseudo-mean correction factor for the seismic hazard

curves. Dr. Cornell's report is provided as Appendix D. The more

important trends observed are:

The site-to-site variability in the ratio of 85th/median in both the

LLNL and EPRI studies are very similar, for all ground motion cases

reviewed. This result is displayed on Figure 4 which shows the

ratio for a peak ground acceleration of 0.20g for the NPP sites. The

LLNL data shown on Figure 4 includes LLNL-AE5. The range of

the above ratio within either the LLNL or EPRI studies is about a

factor of 2 to 2.5 for the majority of the NPP sites;

The difference in the ratio of the 85th/median between the LLNL

and EPRI studies is very similar in a wide variety of cases. For

peak ground acceleration the difference between LLNL and EPRI is

represented by about a factor of 3 to 3.5 with LLNL-AE5 included,

falling to about a factor of 2 if LLNL-AE5 is not included. This trend

holds true for spectral velocities down to about 2.5 hertz. This trend

is displayed on Figure 5 which shows the geometric mean of the

ratio of the 85th percentile to the median for peak ground

acceleration;