Accident Selection

DOE-STD -3009-94

This subsection should conclude that no large release with the potential to

cause significant environmental insult exists that an obvious and eas ily

implemented design or operational change could minimize. For example,

consider widespread river or groundwater contamination due to spills from the

contents of a tank. It would not be an appropriate conclusion to accept such a

risk if a simple dike around the tank would alleviate the problem and yet had

not been installed. Conversely, consider the handling of plutonium in a facility

with gloveboxes, ventilation zones of confinement, and HEPA filters. These

measures would be adequate for closure of e nvironmental contamination

concerns for process accidents. In the majority of instances, process related

TSRs and safety SSCs assigned for defense in depth might be sufficient to

address environmental concerns.

This subsection is not intended to present detailed, cost-benefit conclusions

about the adequacy of design related to potential environmental contamination.

It may serve as input to separate cost-benefit analysis to determine if additional

preventive or mitigative features are to be added to the facility. However, such

analyses are not related to the DSA effort.

The numerical Evaluation Guideline and legal limits on normal operations [i.e.,

Environmental Protection Agency (EPA) regulations] inherently place an

upper bound on potential environmental releases. Further, issues of

environmental contamination are not direct safety issues. Safety SSC

designations are not required for issues solely related to environmental

protection. In accordance with 10 CFR 830, TSR designations are not required

for such issues either. TSR designation associated with prevention of

uncontrolled release of hazardous materials would typically be assigned for

defense- in-depth considerations.

3.3.2.3.5

Accident Selection

Accident analysis entails the formal quantification of a limited subset of

accidents (i.e., DBAs). These accidents represent a complete set of bounding

conditions. The identification of DBAs results from the hazard evaluation

ranking of the complete spectrum of facility accidents.

Figure 3-2 and Tables 3-3 through 3-5 provide examples of hazard evaluation

ranking mechanisms. Two examples are provided to indicate there is more

than one correct approach. The approach used at any specific facility is based

on the detail needed for a given facility and the experience of the analysts.

Figure 3-2 is a graphical example of a common three-by-three frequency and

consequence ranking matrix. This particular example was used for evaluating

airborne hazardous

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