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Facilities, DOE-HDBK-30 10-94 (Ref. 8), for radioactive material release scenarios. Scenario
consequences were then determined using: (1) the ISTs; (2) estimates of applicable, facility
leakpath factors; (3) Site atmospheric dispersion values; (4) receptor breathing rates for
radioactive material releases; and (5) dose conversion factors for radioactive material releases.
Risk classifications of the bounding accident scenarios were then determined using a qualitative
binning methodology based on the refined accident frequency and the newly determined
quantitative estimates of accident consequence.
In those cases where a bounding accident scenario was determined to present a high risk,
evaluations were performed to identify any additional preventive or mitigative features that
could be used to lower the scenario risk. This evaluation was presented in the Control Set
AdequacyNuInerability section of each accident scenario. The adequacy of and vulnerability
associated with credited preventive and mitigative features were presented for each accident
scenario. Risk dominant accident scenarios (i.e., sceneos presenting the highest risk following
the crediting of preventive and mitigative features) at the completion of the Safety Analysis
evaluations were then presented incorporating the results of the discussion in the Control Set
AdequacyNulnerability section (this discussion has been repeated in this chapter in Section 4.6).
4.3.2 Risk Classification Methodology
The risks associated with postulated accident scenarios identified in the hazard evaluation
tables or evaluated as bounding accident scenarios, as discussed in the previous section, were
categorized according to a combmation of the scenario frequencies and consequences, as shown
in Table 4-1. The categorization bins accident scenario risk into one of four risk classes. For the
purpose of this document, risks associated with Risk Class I accident scenarios were considered
major, risks associated with Risk ClassII scenarios were serious, Risk ClassIII accident
scenario risks were marginal, and Risk Class N accident scenario risks were considered
negligible. In addition, Risk Class I and II accident scenarios were considered to be high-risk
scenarios, and Risk Class III and N scenarios were considered to be low-risk scenarios. The risk
class associated with each of the accident scenarios identified and evaluated in NSTR-011-98
was determined based on the Table 4-1 categorization scheme.
HIGH
MODERATE
LOW
Table 4-1 Risk Classes - Frequency Versus Consequence
-
Il I I
m II I
-I
IV m III
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