Accident Analyses

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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