The Nuclear Regulatory Commission will hold an extraordinary meeting next week to appeal the Osaka District Court's decision on the 4th to revoke the decision of the country that allowed the installation of nuclear power plants over the Oi nuclear power plant in Fukui prefecture. We will consider how to deal with it.

On the 4th, the Osaka District Court handed down a ruling to revoke the permission of Kansai Electric Power's Oi Nuclear Power Plant Units 3 and 4 in a trial in which residents requested that the decision of the Nuclear Regulatory Commission that allowed the installation be revoked. ..



This is the first judicial decision to revoke the permission to install a nuclear power plant since the new regulatory standards were established based on the lessons learned from the Fukushima Daiichi nuclear power plant accident.



In the trial, the issue is the expected shaking of the earthquake and the setting of the "standard ground motion", and although there is "variation" in the result of the formula used for calculation, whether the regulatory committee should reflect the "variation" in the examination "There are mistakes and omissions in the judgment process," he said.



On the other hand, the national side argued that the residents' interpretation of "variation" was wrong, and that the standard ground motion had already been sufficiently evaluated by the safe side, and "a sufficient understanding of the court's claim was obtained. I don't think it was there. "



The Regulatory Commission will hold an extraordinary meeting on the 8th of this month in consultation with the relevant ministries and agencies to consider measures, including appeals.

Some experts question how to use formulas

At the time of the examination of the Oi nuclear power plant, which was aiming for restart, Kansai Electric Power Co., Inc. initially had a policy of taking seismic measures such as equipment and piping with a standard ground motion of "maximum 700 gal".



In response, the NRA called for a strict review of the standard ground motion assumptions during the review.



Specifically, the number of interlocking active faults in the surrounding area may be increased from the initial two to three to extend the length of the active faults, or the depth of the epicenter may be shallowed from the initial 4 km to 3 km. After that, he said that the standard ground motion should be derived.



As a result, Kansai Electric Power Co., Inc. has set the standard ground motion as "maximum 856 gal", which is stricter than the beginning, and has taken seismic measures, and the Regulatory Commission has justified this.



The formula called "Irikura / Miyake formula" was used to calculate this "856 gal".



This is a calculation formula that calculates the magnitude of an earthquake from the area of ​​active faults and the depth of the epicenter assumed around the Oi nuclear power plant based on past earthquakes that actually occurred.



In the examination, the result derived from this formula is further multiplied by 1.5.



This is to take into account the uncertainty of the earthquake.



Since the evaluation is on the safety side in this way, the Regulatory Commission is not considering whether to add numerical values ​​based on the "variation" of the earthquake scale pointed out by this judgment. ..



Regarding the examination, some experts questioned how to use the formula.



Mr. Kunihiko Shimazaki, a former member of the Regulatory Commission who was in charge of the examination of the earthquake assumption at the Oi Nuclear Power Plant, and an emeritus professor at the University of Tokyo.



Former Commissioner Shimazaki said that the "Irikura-Miyake type" is not appropriate for earthquake prediction because the exact area of ​​the fault that is the epicenter is not known, and the standard ground motion may be underestimated at the Oi nuclear power plant. It is.



Former Commissioner Shimazaki made this point to the Regulatory Commission in 2016.



When the Regulatory Commission made an earthquake assumption using a formula different from the "Irikura / Miyake formula", reliable results were not obtained, and the "Irikura / Miyake formula" formula is valid. It is said.



For this reason, the Regulatory Commission does not need to revise the standard ground motion of "maximum 856 gal".