Plant states shall be identified and shall be grouped into a limited number of categories primarily on the basis of their frequency of occurrence at the nuclear power plant.
Plant states shall typically cover:
- Normal operation
- Anticipated operational occurrences, which are expected to occur over the operating lifetime of the plant
- Design basis accidents
- Design extension conditions, or beyond design basis including accidents with core melting
Criteria shall be assigned to each plant state, such that frequently occurring plant states shall have no, or only minor, radiological consequences and plant states that could give rise to serious consequences shall have a very low frequency of occurrence.
ANSI Standards cover a wide range of subjects. Certain ANSI standards were written to amplify the general design criteria of 10CFR 50 Appendix A. For example, ANSI standard 18.2 defines the following design condition categories:
- Condition I – Normal Operation
- Condition II – Incidents of Moderate Frequency
- Condition IIl – Infrequent Incidents
- Condition IV – Limiting Faults
See also: ANSI ANS 51.1: Nuclear Safety Criteria for the Design of Stationary Pressurized Water Reactor Plants, 1983.