A criterion for determining exceedance of the operating basis earthquake: Final report

A criterion is recommended for determining whether the Operating Basis Earthquake (OBE) has been exceeded after the occurrence of a seismic event at a nuclear power plant. The technical procedure provides a fast and effective means for assessing the damage potential of any ''felt'' earthquake in the first few hours after occurrence. For OBE exceedance to occur, the recommended criterion requires exceedance of both a response spectrum parameter and a second damage parameter, referred to as the Cumulative Absolute Velocity (CAV). The detailed operational requirements for implementing the criterion are provided. The criterion was developed, based on a study of earthquake damage to conventional buildings, review of past damage to power plants and heavy industrial facilities, blast damage, fragility data and equipment vibration performance, to ensure that ground motions greater than Modified Mercalli Intensity VI are conservatively identified as exceeding the OBE. Based on direct correlations of the criterion parameters with damage data, ground motions which cause damage to buildings of good design and construction (which in general are not as seismically strong as nuclear facilities) are a factor of at least 1.5 larger than the recommended criterion threshold values. This ensures adequate conservatism in the criterion. Issues related to OBE exceedance, including the history of the OBE, regulatory and operational issues, plant operation concerns, current industry activities related to OBE exceedance and recent earthquake experience are discussed in the report