ANS RA-S-1.4-2021

ANSI/ASME/ANS RA-S-1.4-2021 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, andexternal 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.

Keywords: non-light water reactors (non-LWRs), small modular reactors (SMRs), liquid metal-cooled fast reactors (LMRs), molten salt reactors, microreactors (MSRs), high-temperature gas-cooled reactors (HTGRs), modular high-temperature gas-cooled reactor (MHTGR)

Product Details

ANSI Approved
Number of Pages:
File Size:
1 file , 6.3 MB
Product Code(s):
240338, 240338, 240338