3:45 PM - 4:00 PM
[HCG27-02] Changes in the Treatment of Scientific Issues in Nuclear Power Plant Trials
★Invited Papers
Keywords:Nuclear Power Plant Trials, Scientific Issues, Changes in the Treatment
Since strong ground motions causing damage to nuclear power plants are rare phenomena, it is difficult to state with certainty whether or not they occur in several ten years, which is the operating period of nuclear power plants, and such scientific issues involve large incertitude. However, in order to make a serious conclusion to stop the operation of a nuclear power plant, it is necessary to carry out the reasoning which is deterministic to some extent, and in the judgments until now, there were many unreasonable things on the scientific issues. However, in the judgment of Osaka District Court on "request for an order to suspend operation of the Oi nuclear power plant" in December, 2020, unreasonable reasoning was not carried out for the scientific issues in Point 2 (Rationality of the formula of Irikura and Miyake and the formula of Dan et al.) and Point 3 (Rationality of using the seismic moment calculated based on the Irikura-Miyake formula as the seismic moment of a source model). Instead, the main issue was the failure of the defendant (the electric power company) to comply with "variation clause" ("When the earthquake scale is set using an empirical formula which relates the length or area of the source model or the fault displacement in a seismic cycle with the earthquake scale, it is necessary to also consider the variation of an empirical formula, because an empirical formula ( . . . ) gives the earthquake scale as an average value.") in the Seismic Ground Motion Review Guide. In other words, the incertitude in scientific issues was avoided by replacing it with a procedural problem.
Until then, it had been considered that the variation in the calculation of earthquake scale had been already taken into consideration by conservatively setting an earthquake source model (i.e., the model is set on the safe side), however, in the judgment, it is considered that the latter half of "variation clause" had to be taken into consideration explicitly and independently, because it was specially added in March 2012. Furthermore, one of the reasons why it is reasonable to use the Irikura-Miyake formula for the source fault as the result of active fault investigation from the ground surface is that the source model is set conservatively, so it is not appropriate to use it as a double reason.
Until then, it had been considered that the variation in the calculation of earthquake scale had been already taken into consideration by conservatively setting an earthquake source model (i.e., the model is set on the safe side), however, in the judgment, it is considered that the latter half of "variation clause" had to be taken into consideration explicitly and independently, because it was specially added in March 2012. Furthermore, one of the reasons why it is reasonable to use the Irikura-Miyake formula for the source fault as the result of active fault investigation from the ground surface is that the source model is set conservatively, so it is not appropriate to use it as a double reason.