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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


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