Part A- Comments - Continued

DOE-STD-1024-92

NS-4

By introducing a "pseudo-mean correction factor," the draft interim position

allows for the use of the median seismic hazard curves, which are more stable

than mean seismic hazard curves. We believe the general approach

developed by the SWG is rational and practical. However, as noted in the

SWG report (in the penultimate paragraph of Page 12), there are recent

indications that the factor of 1.65 given in Item A.3 of the position may not be

appropriate for earthquakes with annual probabilities of 1 X 10-3 or greater.

As with the slope issue, corrections to the pseudo-mean correction factor

would also tend to raise the earthquake review levels for facilities not classified

as high hazard.

NS-5

The issues discussed above raise a more general concern that, ironically, the

seismic criteria developed for lower probability earthquakes (i.e., those less

likely to occur) appear to be the most robust. This is probably because of all

the attention that the technical community has given to the use of seismic

hazard curves for commercial nuclear reactor seismic evaluations. For

commercial reactors, annual earthquake probabilities of 1 x 10-3 or greater are

of low interest since they are below safe shutdown earthquake levels and do

not control risk. The DOE seismic criteria effort needs to be much more

focussed towards higher probability earthquakes.

NS-6

Section B of the draft interim position introduces correction factors for cases

where only the EPRI or LLNL curves exist. Our calculations indicate that the

1.3 factor for adjusting LLNL medians is too high. The attached table on

"Calculation of Earthquake Levels Using DOE SWG Draft Interim Position"

shows that this factor underpredicts the results obtained from using both the

EPRI and LLNL curves. We recommend that the correction factors given in

Section B be re-evaluated considering a wider data base than shown in Table

3, including consideration that these factors may vary with earthquake annual

probabilities and could be different for the EPRI and LLNL curves.

NS-7

Part C of the draft interim position (on page 3) provides guidance on

developing site-specific spectra. This guidance is somewhat independent from

the rest of the material in the SWG's report, and there is very little discussion

on the technical basis for Part C. Additional justification should be written if the

SWG's report is to be finalized, and the criteria and justification should be

incorporated within NE-70's natural phenomena guidelines.

A-3