-- Identification of the limited set of unique and representative accidents (i.e.,
DBAs) to be assessed further in accident analys is.
Accident analysis of DBAs identified in the hazard analysis. The summary of this
activity will include for each accident analyzed, the following:
-- Estimation of source term and consequence.
-- Documentation of the rationale for binning frequency of occurrence in a
broad range in hazard analysis (detailed probability calculations not
-- Documentation of accident assumptions and identification of safety-class
SSCs based on the Evaluation Guideline.
Existing supporting documentation is to be referenced. Include brief abstracts of
referenced documentation with enough of the salient facts to provide an understanding of
the referenced documentation and its relation to this chapter.
APPLICATION OF THE GRADED APPROACH. The results of the hazard
analysis provide a comprehensive evaluation of the complete DSA accident spectrum.
This evaluation will be essentially qualitative in that its aim is to produce a well-reasoned
and clear assessment of facility hazards and their associated controls. The focus of hazard
analysis is on the completeness of consideration given to the accident spectrum, as
opposed to a formalized definition of accident sequences and assumptions. Summary
discussion of methodology is appropriate, but detailed bases for judgment and any s imple
mathematical estimates used in the hazard analysis to guide the judgments of the analysis
for specific accident scenarios are not required to be formally documented in the DSA. For
a small subset of accidents, the accident analysis documents individ ual calculations in the
DSA, including references to its supporting documents. The accident analysis only needs
to provide sufficient calculations to support a comparison to the Evaluation Guideline for
the purpose of identifying safety-class SSCs.
In general, a graded approach dictates a more thoroughly documented assessment of
complex, high hazard facilities than simple, lower hazard facilities since grading is a
function of both hazard potential and complexity. The basic elements of hazard
identification, categorization, evaluation, and analysis are required for any facility
preparing a DSA in accordance with 10 CFR 830. The graded approach for hazard
analysis is a function of selecting techniques for hazard evaluation. The techniques used
for hazard evaluation can range from simple checklists or What-If analyses to systematic
parameter examinations such as Hazard and Operability Analyses (HAZOPs). The
technique selected need not be more sophisticated or detailed than is necessary to provide a
comprehensive examination of the hazards associated with the facility operations. For
example, a simple storage operation may be adequately evaluated by a preliminary hazard
analysis or a structured What-IF analysis. There is no obligation for the analysts to
perform a complete HAZOP.
To achieve the objectives of analysis of accidents, the graded approach ranges from a
hazard analysis to a detailed quantitative analysis where formally quantified event trees