Seismic Damage Indicating Parameters at Nuclear Power Plants Affected by the 2011 Tohoku-Oki Earthquake and Plant Shutdown Criteria

A rational and quantitative shutdown criterion is required for a nuclear power plant in response to seismic shaking to determine whether the plant must be shut down for inspection. The shutdown criterion is generally defined in terms of seismic damage indicating parameters. This paper presents seismic damage indicating parameters of the recorded free-field and in-structure motions at the Onagawa, Fukushima Daiichi, Fukushima Daini, and Tokai Daini nuclear power plants during the 2011 Tohoku-oki earthquake. The observed seismic damage indicating parameters largely exceed the current U.S. and Japan shutdown thresholds for nuclear power plants, while minimal damage due to ground shaking was observed at the four Japanese plants. These observations indicate a potential for raising the current threshold without introducing any significant additional seismic risk to nuclear power plants. The insights presented in this paper can be used to guide regulation and industry methods for quickly evaluating the damage potential of future earthquakes that affect nuclear power plants. With some adjustment, a similar methodology and criterion could be applied to conventional structures and lifeline infrastructure.