ASME/ANS RA-S-1.4-2013: Probabilistic Risk Assessment Standard for Advanced Non-LWR Nuclear Power Plants
Scope: This standard establishes requirements for a probabilistic risk assessment (PRA) for advanced non-light water reactor (LWR) nuclear power plants. The requirements in this standard were developed for a broad range of PRA scopes that may include the following:
(a) Different sources of radioactive material both within and outside the reactor core but within the boundaries of the plant whose risks are to be determined in the PRA scope selected by the user. The technical requirements in this trial-use version of the standard are limited to sources of radioactive material within the reactor coolant system (RCS) pressure boundary (RCPB). For pool-type reactors with no RCPB, the scope includes sources within the RCS. Technical requirements for other sources of radioactive material such as the spent fuel system are deferred to future editions of this standard;
(b) Different plant operating states including various levels of power operation and shutdown modes;
(c) Initiating events caused by internal hazards, such as internal events, internal fires, and internal floods, and external hazards such as seismic events, high winds, and external flooding;
(d) Different event sequence end states, including core or plant damage states (PDSs), and release categories that are sufficient to characterize mechanistic source terms, including releases from event sequences involving two or more reactor units or modules for PRAs on multireactor or multiunit plants;
(e) Evaluation of different risk metrics including the frequencies of modeled core and PDSs, release categories, risks of off-site radiological exposures and health effects, and the integrated risk of the multiunit plant if that is within the selected PRA scope. The risk metrics supported by this standard are established metrics used in existing LWR Level 3 PRAs such as frequency of radiological consequences (e.g., dose, health effects) that are inherently technology neutral. Surrogate risk metrics used in LWR PRAs such as core damage frequency and large early release frequency are not used as they may not be applicable to non-LWR PRAs;
(f) Quantification of the event sequence frequencies, mechanistic source terms, off-site radiological consequences, risk metrics, and associated uncertainties, and using this information in a manner consistent with the scope and applications PRA.