scope:

This Standard states requirements for a PRA for advanced non-LWR NPPs. 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 but within the boundaries of the plant whose risks are to be determined within the PRA scope selected by the user;

(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. The only hazards explicitly excluded from the scope are releases resulting from purposeful human-induced security threats (e.g., sabotage, terrorism);

(d) Different event sequence end states, including those with no adverse consequences, plant damage states (PDSs), and release categories that are sufficient to characterize mechanistic source terms, including releases from event sequences involving two or more reactors or radionuclide sources;

(e) Evaluation of different risk metrics including the frequencies of modeled PDSs, event sequence families, release categories, risks of off-site radiological exposures and health effects, and the integrated risk of the multi-reactor plant as defined by the selected PRA scope. The risk metrics supported by this Standard are established metrics used in existing light water reactor (LWR) Level 3 PRAs such as frequency of radiological consequences (e.g., dose, health effects) that are independent of reactor technology. Surrogate risk metrics used in LWR PRAs such as core damage frequency (CDF) and large early release frequency (LERF) are not applicable to many non-LWR designs and not used in this Standard;

(f) Quantification of the event sequence frequencies, mechanistic source terms, off-site radiological consequences, risk metrics, and associated uncertainties, and using this information to support risk-informed decisions in a manner consistent with the scope and applications PRA.

Technical requirements are provided in this Standard for different combinations of sources of radioactive material, plant operating states, and hazard groups. In this Standard, the technical requirements for the internal fire hazard group are limited to "at-power" plant operating states as there was insufficient experience in performing internal fire PRAs during low power and shutdown (LPSD) plant operating states to justify the inclusion of such requirements. This exclusion is consistent with supporting LWR PRA standards. Other combinations of hazard groups and plant operating states are, however, supported in this Standard.

It is recognized that for some PRA applications, a PRA that addresses the full set of requirements covered in this Standard may not be required. In addition, for PRAs performed in various stages of design and licensing, especially those PRAs performed prior to the selection of a specific site, the level of detail and completeness of the PRA with respect to the PRA scope, coverage of events and event sequences, plant operating states, hazards, risk metrics, and operational characteristics may be limited in relation to that for typical PRAs for an operating plant. Hence, the scope of the PRA is established by the user in accordance with the intended PRA applications and the availability of information to support each PRA element. In addition, the requirements in this Standard for the level of detail, completeness, and model to plant or design fidelity vary according to the scope and level of detail of design and operational information that is available to support, and is referenced by, the PRA with additional requirements to address assumptions in lieu of as-operated and as-built details.

Hazards explicitly excluded from the scope of this Standard are radionuclide releases resulting from purposeful human-induced security threats (e.g., sabotage, terrorism) and risks associated with accidental radiological exposures to on-site personnel. This Standard applies to PRAs used to support applications of risk-informed decision-making (RIDM) related to design, licensing, procurement, construction, operation, and maintenance of advanced non-LWR NPPs.

This Standard includes requirements for addressing the off-site radiological consequences of event sequences involving the release of radioactive material from the plant. The consequence metrics are common to those found in LWR Level 3 PRAs. The scope of these requirements excludes the consideration of radiological or other consequences to on-site personnel.