Assumptions

DOE-STD-1024-92

3.0

ASSUMPTIONS

Based on the above conclusions, the following assumptions have been

developed by the S WG.

The Standard should result in a consistent estimate of probabilistic

seismic hazard (degree of conservatism) from site to site. The

relative consistency from site to site is an important element in

implementing the criteria in UCRL 15910 (DOE-STD-1020) (e.g.,

UCRL 15910 (DOE-STD-1020) performance goals and hazard

exceedance probabilities are predicated on the use of consistent

hazard estimates).

Use of either the LLNL and EPRI results should not be to the

exclusion of the other. While specific portions of each study have

come under question, the studies represent landmarks in the

assessment of probabilistic seismic hazard, and should both be used

to make seismic decisions.

Uncertainty should be explicitly incorporated into the selection of the

ground motion at a given probability of exceedance.

The mean seismic hazard curve should be used if the criteria are

associated with single value probabilistic seismic hazard input, such

as the hazard exceedance probabilities defined in UCRL-15910

(DOE-STD-1020). If there is doubt that existing mean estimates are

realistic (as is the case) then a pseudo-mean should be developed.

Given the current concerns with both the LLNL and EPRI results the

pseudo-mean should not be based on the fractiles below the 15th

percentile and above the 85th percentile from either study. The use

of mean estimates is incorporated in the DOE Natural Phenomena

Hazards Mitigation Order (DOE Order 5480.NPH).

When available, site specific soil conditions should be explicitly

included in the seismic hazard estimates, and in the development of

an appropriate response spectra. For soil sites, an explicit

determination should be made to assess the potential for site

amplification.