New Method for Evaluating Earthquake Safety of Aging Nuclear Reactor Piping JAEA Develops Code to Calculate Seismic Fragility

The Structural Integrity Research Group of the Nuclear Safety Research Center (NSRC), Japan Atomic Energy Agency (JAEA), has developed a new code, entitled PASCAL-SP2, for evaluating the seismic fragility, or chance of earthquake damage, of reactor piping in long-term use as part of their research on evaluating the earthquake resistance of equipment in nuclear power plants. This is the first code of its kind in the world, and was released after verifying its accuracy.

Reactor piping can be damaged from the seismic activity of massive earthquakes that exceed the original design parameters of the reactor, but to date there had been no method for calculating the likelihood that reactor piping might be damaged in a manner that took into account the wear and tear of the piping from long-term use.

Accordingly, the research group used systematic experimentation and numerical analysis to establish a new method to evaluate the degree of cracking to expect from the seismic activity caused by a major earthquake that exceeds design parameters. This method was then included in the PASCAL-SP code for determining the likelihood of earthquake damage to develop the only code in existence for calculating the seismic fragility of reactor piping subject to long-term use. The group also compiled evaluation procedures, and prepared evaluation guidelines of high benefit to users for publication along with the code.

Group leader Yinsheng Li stated, "In the future, we hope to carry out quantitative analysis of the safety and margin of error of reactor piping subject to long-term use when it is effected by earthquake tremors using the analysis code and evaluation guidelines. By doing so, we intend to contribute to the utilization of risk data, including safety evaluations of existing nuclear power plants."

* The usage manual for PASCAL-SP2 was published as JAEA-Data/Code 2020-021, and the evaluation criteria as JAEA-Research 2020-017, both on February 25. The analysis code package can be obtained via the PRODAS program and database retrieval system (http://prodas.jaea.go.jp) run by JAEA.

■ Seismic Fragility: the percent chance that pipes or other equipment will be damaged by different degrees of earthquake tremors. The seismic fragility curve describes the relationship of the probability of damage versus the magnitude of the earthquake tremors.