Part A- Comments - Continued

DOE-STD-1024-92

clarification on the document's usage to clear up the confusion. Two problems

have been found. The first is the use of UCRL-15910 as a facility hazard

classification guide. The second is in the selection of the design basis accidents

(DBA) to be used in the analyses.

First, the UCRL document is not a hazard classification guide. The facility hazard

classification is to be determined independently of UCRL-15910. The AL Waste

Management and Operations Surety Division has recommended the use of the

Pacific Northwest Laboratory-Lucas (PNL-Lucas) method until specific guidance

is issued by DOE Headquarters (HQ). Once the hazard class is determined, the

class is used in UCRL-15910 to determine the facility Usage Category. This

usage category is used to determine the DBA probabilities of occurrence.

Second, there has been confusion in the interpretation of the DBA occurrence

probability. The document presents two different probabilities, the performance

goal probability and the exceedance probability. The performance goal

probability is lower (less frequent, but higher consequence events) than the

hazard exceedance probability (more frequent, but lesser consequences).

There are two ways to approach these probabilities. First, the facility DBA can be

based on the event severity corresponding to the nominal performance goal

probabilities (median centered approach); that is, basing the nominal design on

the performance goal probability without including safety factors. This approach

is considered to be controversial and not well understood. Second, it can be

based on the traditional conservative approach of using the event severity

corresponding to the hazard exceedance probability with all the UCRL-15910

recommended safety factors (higher probability of occurrence, lower

consequence event plus safety factors). This latter approach is the one most

often used in assessing facilities because it is a better documented and

understood approach. Appropriately used, the authors state that either approach

is acceptable.

The seismic event performance goal and exceedance probabilities are presented

in Table 2-3 (Pages 2-6) and in the table on Page A-2. The wind and tornado

probabilities are presented in Table B-3 (Page B-4). Because there is no

performance goal probability for flood events, the hazard exceedance

probabilities in Table 6-1 (Page 6-2) are used.

UCRL-15910 may be used for facilities at sites without site-specific data. Site-

specific data should be used if it is available. The language and discussions in

the SARS should reflect the terminology and content used in the UCRL

document.

NV-1

The subject document has been reviewed, and we have no comments.

Considering the circumstances, the "Interim Position" regarding the use of the

LLNL and the EPRI probabilistic seismic hazard curves at DOE sites is a

reasonable approach until the issue is resolved in 18 to 24 months.

A-13