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.
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