How much can the piping systems in nuclear reactors withstand a massive earthquake?
—Development of a seismic safety assessment method for the piping systems used in long-term operated nuclear reactors—
When a massive earthquake strikes, the response waveform may result in the failure of the piping systems in nuclear reactors. While the failure probability due to earthquake varies depending on the degree of age-related degradation of the piping systems used in long-term operated nuclear reactors, no method had been proposed for this kind of failure probability evaluation up to now .
The Japan Atomic Energy Agency (JAEA) has developed the first analysis code in the world for the failure probability evaluation of the piping systems due to earthquake in consideration of factors such as the piping material properties, the usage environment, and the degree of age-related degradation. After a series of verification activities, the analysis code has been released to the public.
Furthermore, for the piping systems used in long-term operated nuclear reactors, JAEA has also developed a guideline for the first time in the world, in which, the evaluation procedures, the recommended methods and probabilistic evaluation models, and the technical bases for the failure probability evaluation due to earthquakes are provided. The guideline has also been published following the review by outside experts in different fields.
The result of this study is important to realistic assessment on the probabilistic seismic risk for nuclear reactors under long-term operation. For example, the improvement effects of maintenance activities on seismic margins are able to be quantitatively evaluated. Therefore, the analysis code and the guideline are expected to contribute to risk-informed applications such as safety improvement assessments.