ANS 2.23

Abstract

Scope: This standard1) is a major update of ANSI/ANS-2.23-2002 (R2009) [1]2). It describes actions that the owner of a nuclear power plant shall take to prepare for and respond to a felt earthquake at the plant(s), including the need for plant shutdown; actions to determine the readiness of the plant to resume operation; and those evaluations necessary to verify the long-term integrity of safety-related (SR) and important structures, systems, and components (SSCs). It also includes a consensus definition of operating basis earthquake (OBE) exceedance, beyond which U.S. regulations require plant shutdown. Application of this revised standard provides a comprehensive, balanced plan for the response of a nuclear power plant to an earthquake. This standard does not cover those operator actions that are performed in connection with safe operation and control of the nuclear power plant during and following an earthquake. These operations are specified in plant operating procedures, emergency procedures, alarm response procedures, and other conditions of the plant’s license. Likewise, it does not cover required reporting and communications with the U.S. Nuclear Regulatory Commission (NRC). It is not applicable to nuclear facilities other than licensed nuclear power plants. Purpose The purpose of this standard is to specify actions that shall be included in plant-specific procedures that describe actions to be taken in preparation for and response to a felt earthquake at the plant. The objectives of these procedures are to determine the following: • the effects of the earthquake on the physical condition of the nuclear power plant; • whether shutdown of the plant is required, based on observed damage to the plant or because the OBE has been exceeded; • the readiness of the plant to shut down if shutdown is required due to an earthquake; • the readiness of the plant to resume operation from a shutdown condition based on physical inspections and tests and the successful completion of operability tests and analytical evaluations, where required, that demonstrate that the limiting conditions for operation as defined in the plant technical specifications are met. The combination of the preparatory, short-term, post-shutdown, and long-term actions provides a rational, experience-based approach for determining the real damage potential of a felt and recorded earthquake, a systematic methodology for assessing plant readiness for restart based on physical inspections and tests and on realistic criteria for assuring the long-term integrity of the power plant. These actions also minimize the likelihood of prolonged plant shutdowns following nondamaging seismic disturbances and place primary emphasis on the physical and functional conditions of the plant as a measure of restart readiness, as opposed to relying primarily upon analytical evaluations and instrumental data alone. 1) The current standard, ANSI/ANS-2.23-2016, is herein referred to as “this standard.” 2) Numbers in brackets refer to corresponding reference numbers in Sec. 10, “References.”