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DOE-STD -3009-94
ion exchange column or a red oil explosion at a facility where the phenomena is
physically possible and documentation is not available substantiating ventilation and
building confinement systems were specifically designed for such an occurrence. For
natural event accidents, derivative DBAs are defined by a frequency of initiator based on
DOE 420.1, "Facility Safety", and its associated implementation standards. For external
man-made accidents, derivative DBAs are assumed if the event can occur with a
frequency >10-6/yr as conservatively estimated, or >10-7/yr as realistically estimated. Use
of a frequency cutoff for external events represents a unique case for external events
only, based on established Nuclear Regulatory Commission (NRC) precedents. For
simplicity, use of the term DBA throughout this Standard is inclusive of both DBAs and
derivative DBAs.
ACCIDENT ANALYSIS
The complete spectrum of accidents is examined in hazard analysis. A limited subset of
accidents, (i.e., DBAs and derivative DBAs) that bound "the envelope of accident
conditions to which the operation could be subjected" are carried forward to accident
analysis where safety-class SSCs are designated by comparison of accident consequences
to the Evaluation Guideline. These scenarios are the accidents requiring formal definition.
Information obtained from specific accidents or representative accidents enveloping many
small accidents is used to specify functional requirements for safety-class SSCs in
Chapter 4.
An accident analysis is performed for the bounding accidents. Accident analysis in this
Standard refers to the formal quantification (i.e., all assumptions identified and justified
and individual computations presented or summarized) of accident consequences. The
general binning estimates used in hazard analysis are adequate and representative of the
level of effort desired for frequency determination. Accordingly, accident analysis need
only document the basis used in hazard analysis for assigning accident likelihood to two -
orders-of-magnitude bins. The quantified consequences are compared to the numerical
Evaluation Guideline for the purpose of identifying safety-class SSCs and any accident
specific assumptions requiring coverage by TSRs.
APPLICATION OF THE GRADED APPROACH
10 CFR 830 prescribes the use of a graded approach for the effort expended in safety
analysis and the level of detail presented in associated documentation. The graded
approach applied to DSA preparation and updates is intended to produce cost efficient
safety analysis and DSA content that provide adequate assurance to the DOE that a
facility has acceptable safety provisions without providing unnecessary information. As
described in 10 CFR 830, the graded approach adjusts the magnitude of the preparation
effort to the characteristics of the subject facility based on seven factors:
The relative importance to safety, safeguards, and security;
The magnitude of any hazard involved;
The life cycle stage of a facility;
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