ANSI/ANS 58.21-2003

The scope of a PRA covered by this standard is limited to analyzing accident sequences initiated by external events that might occur while a nuclear power plant is at nominal full power. It is further limited to requirements for (a) a Level 1 analysis of the core damage frequency (CDF) and (b) a limited Level 2 analysis sufficient to evaluate the large early release frequency (LERF). The scope of a seismic margin assessment (SMA) covered by this standard is limited to analyzing nuclear power plant seismic capacities according to either the so-called Electric Power Research Institute (EPRI) method (EPRI Method) or the so-called U.S. Nuclear Regulatory Commission (NRC) method (NRC Method).

In some places in this standard, the phrase seismic PRA is used in a generic sense. Often, for example, in most of the language in Section 1, the intent is to include SMA methods as well as seismic PRA methods within the scope of the acronym PRA. For example, both PRA and SMA methods are contemplated as being considered together for the broad purposes of 1.4 through 1.10, even though the language sometimes uses PRA alone. Of course, the context of each individual passage will indicate whether a distinction is made between PRA and SMA.

External events covered within this standards scope include both natural external events (e.g., earthquakes, high winds, and external flooding) and human-made external events (e.g., airplane crashes, explosions at nearby industrial facilities, and impacts from nearby transportation activities). Appendix A contains an extensive list of most of the external events generally included within an external-events PRA and hence within this standards scope.