ANSI/ASME/ANS RA-S-1.4-2021规定了先进非轻水堆核电站PRA的要求。本标准中的要求适用于范围广泛的PRA范围，可能包括以下内容:（a）反应堆内外但在电厂边界内的不同放射性物质源，其风险将在用户选择的PRA范围内确定；（b） 不同的电厂运行状态，包括不同级别的功率运行和停机模式；（c） 由内部危险引起的始发事件，如内部事件、内部火灾和内部洪水，以及 外部危险，如地震、大风和外部洪水。明确排除在范围之外的唯一危险是人为安全威胁（如破坏、恐怖主义）造成的释放；（d） 不同的事件序列终态，包括无不良后果的事件序列终态、电厂损害状态（PDS）和足以表征机械源项的释放类别，包括涉及两个或多个反应堆或放射性核素源的事件序列的释放； （e） 评估不同的风险指标，包括建模PDS的频率、事件序列系列、释放类别、场外辐射暴露和健康影响的风险，以及所选PRA范围定义的多反应堆电厂的综合风险。本标准支持的风险指标是现有轻水反应堆（LWR）3级PRA中使用的既定指标，例如独立于反应堆技术的辐射后果频率（如剂量、健康影响）。轻水堆PRA中使用的替代风险指标，如堆芯损坏频率（CDF）和大型早期释放频率（LERF），不适用于许多非轻水堆设计，也不适用于本标准；（f） 事件序列频率、机械源项、场外辐射后果、风险度量和相关不确定性的量化，并使用这些信息支持风险评估- 以符合PRA范围和应用的方式做出明智的决定。关键词:非轻水反应堆（非轻水堆）、小型模块化反应堆（SMR）、液态金属冷却快堆（LMR）、熔盐反应堆、微反应堆（MSR）、高温气冷反应堆（HTGR）、模块化高温气冷反应堆（MHTGR）

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, 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.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)