Product Abstract

Guidelines for nuclear plant response to earthquakes enable utilities to quickly evaluate the need for post-earthquake plant shutdown and provide procedures for evaluation of earthquake effects on the plant, as well as criteria for plant restart. The procedures enable the responding team of operators and engineers to identify and assess any earthquake effects and, if shutdown is necessary, to return the plant to safe operation as rapidly as possible.

Background

Small, nondamaging earthquakes may exceed the operating basis earthquake (OBE) spectrum in the high-frequency range without causing damage. EPRI report NP-5930 provides an analytical criterion for determining when an OBE is exceeded. However, a comprehensive plan for plant response must include provisions for assessing plant physical condition and readiness for shutdown, shutdown decision criteria, and procedures for plant evaluation and return to service.

Objective

To develop guidelines for nuclear plant response to an earthquake.

Approach

The guidelines were developed by a team with expertise in system performance, plant operations, and seismic structural engineering disciplines. Based on the knowledge that operating and emergency procedures to respond to plant symptoms are already in place at nuclear power plants, the team formulated comprehensive guidelines for utilities to develop plant-specific procedures for response to an earthquake. Throughout guideline development, a panel of utility and industry experts on plant operation and earthquake engineering provided a comprehensive peer review.

Results

The EPRI guidelines provide for a progressive response to an earthquake. They define immediate actions, as well as post-shutdown and long-term actions. The findings at each stage indicate the need for and the level of any additional effort. The guidelines specify that plant personnel perform initial inspections, gather seismic recordings, and reach decisions on the need for plant shutdown and on plant readiness for shutdown. If the plant is shut down, the guidelines define procedures for near-term actions by plant operators to determine the earthquake's effects, with engineers performing focused baseline inspections to determine if structures have sustained significant damage or if operating systems are in any way impaired. The guidelines then define actions necessary to establish the readiness of the plant to restart. Finally, the guidelines provide for long-term, confirmatory evaluations, which, in most cases, can be performed after plant restart.

EPRI Perspective

The guidelines given in this report recognize the existence of extensive emergency operating procedures used by operators to maintain the plant in a stable condition. In addition, they are based on the knowledge that the operators are intimately familiar with the day-to-day conditions of the plant and can best perform the first assessment of the plant's condition following an earthquake. If shutdown is necessary, seismic/structural engineers are called in to perform more-thorough evaluations. EPRI's guidelines will be most useful for cases in which small earthquakes occur and cause little or no damage. In such instances, use of the guidelines will enable the utility to rapidly establish that the plant can continue or resume operation. In the extremely unlikely event that potentially damaging ground motions should occur at a site, implementation of EPRI's procedures will minimize the time needed to assess the impact on plant components and systems and provide assurance that the plant can safely operate.