Hokuriku Electric Power's claim that the fault that runs through the site of the Shika Nuclear Power Station in Ishikawa Prefecture is "not an active fault" was generally accepted at the review meeting of the Nuclear Regulation Authority.


Seven years ago, the regulatory committee's expert meeting indicated that "the possibility of future movement cannot be denied" will be changed, and Hokuriku Electric Power will proceed with the examination of Unit 2, which is aiming to restart. Become.

Regarding the Shika nuclear power plant, seven years ago, an expert meeting of the Nuclear Regulation Authority concluded that there was a possibility that part of the fault on the site could move in the future. There was a possibility that Unit 1 would need to be decommissioned, and that Unit 2 would also require major renovations.



Furthermore, in the review of Unit 2 applied for by Hokuriku Electric Power, if even one of the 10 faults running through the site was an active fault, restarting would not be permitted.



In response to this, Hokuriku Electric Power Co., Ltd. presented an evaluation using a new method called the "mineral vein method," which grasps the age of fault movement from the state of minerals contained in the stratum.



As a result of the analysis, no deformation due to the fault was observed in the minerals that are estimated to have occurred more than 6 million years ago.



Akira Ishiwatari, Commissioner of the Nuclear Regulation Authority, said at the review meeting on the 3rd, ``After reassessing based on the huge amount of newly released data, we can judge that there is no possibility of future activity on the fault. We have convincing evidence for



On top of that, at the screening meeting, Hokuriku Electric Power Company's claim that it was not an active fault was generally accepted, stating that it was evaluated as being "generally appropriate."



We will change our view seven years ago, and the examination of Unit 2 will progress.



On the other hand, in the examination, there are many items left, such as assumptions of natural disasters such as earthquakes and tsunamis, and countermeasures against them.

History of the debate over the fault at the Shiga nuclear power plant

There are Units 1 and 2 at the Shika Nuclear Power Plant, and whether or not the fault that runs through the site is an "active fault" that may move in the future, a meeting of experts from the Nuclear Regulation Authority and a review aimed at restarting Unit 2. has been discussed.



Some of the faults on the site were discussed at the Regulatory Commission's expert meeting prior to the review of Unit 2, and an assessment report was compiled in 2016.



At this time, we evaluated the fault "S-1" that runs directly under Unit 1 and the fault that runs directly under the cooling pipes leading to the reactors of Units 1 and 2.



Of these,


the ▽ "S-1" fault is based on the cracks and steps in the underground bedrock marked in the sketch of the trench survey dug right next to the reactor building before the construction of Unit 1 to investigate the strata. “There is no denying the possibility that it will move in the future,” he said.



Also,


regarding the fault that runs directly under the ▽ cooling pipe, he expressed the opinion that "there is a possibility that the ground will be deformed in the future" based on the situation of the stratum from the trench survey.



The new regulatory standards for nuclear power plants do not allow the installation of important facilities on faults that may move in the future. There is a possibility that the cooling pipes leading to the Unit's reactor will need to be relocated or reinforced.



On the other hand, he also pointed out that these evaluations were based on limited data, such as sketches of faults at the time of construction, and that more detailed analysis and data were necessary for more accurate evaluations.



In response to this, Hokuriku Electric Power claimed in the 2014 application review for the restart of Unit 2 that none of the faults on the site, including these faults, "may move in the future." As a basis for this, he presented an evaluation based on a new method called the "mineral vein method."



According to the new regulatory standards for nuclear power plants, faults that are thought to have moved after the ``Late Pleistocene'' era of 120,000 to 130,000 years ago are defined as ``active faults'', and the state of the stratum indicates activity. A method is used to check for the presence or absence of the movement and the age of the shift.



On the other hand, in the case of the Shika Nuclear Power Plant, due to the fact that there are few materials that show changes in the stratum, we adopted a method to determine the age of the fault by examining when the minerals contained in the stratum changed due to the influence of underground heat. bottom.



There were 10 faults on the site that were subject to the review, and if even one was found to be an active fault, the plant would not be allowed to restart.



Hokuriku Electric Power analyzed the samples collected during the drilling survey and found no displacement or deformation due to faults in the minerals that are estimated to have formed more than 6 million years ago. I argued that it could be denied.



In response to this, the regulatory committee observed changes in the stratum around the fault and analysis results of minerals contained in the fault in a field survey, and examined whether Hokuriku Electric Power's claim was appropriate.

History of Shiga Nuclear Power Plant Unit 2

Shika Nuclear Power Station Unit 2 started commercial operation in 2006, 17 years ago.



The Great East Japan Earthquake occurred immediately after starting regular inspections in 2011, and it has been suspended since then.



It was in 2014 that Hokuriku Electric Power Company applied for a conformity review to the Nuclear Regulation Authority based on the newly formulated regulatory standards based on the lessons learned from the Fukushima accident.



During the review process, the problem was a fault that runs through the site, including under the reactor building.



Under the new regulatory standards, important facilities cannot be installed on an "active fault," so Hokuriku Electric Power Company had to show the grounds that it was not an "active fault."



Hokuriku Electric Power uses a technique called the "mineral vein method" to examine whether there is any displacement or deformation in the minerals distributed across the fault, in addition to the method of identifying the age of displacement by examining the strata stacked on the fault. submitted the data.



The regulatory committee evaluated the data from this "mineral vein method", and last year, it proceeded with the determination by conducting a local survey.



After last year's investigation, Regulatory Commissioner Akira Ishiwatari said, "There is no contradiction in Hokuriku Electric Power's explanation. It won't take long to make a decision."

Faults and "mineral vein method" on the site of Shika Nuclear Power Plant

There are multiple faults on the site of the Shika Nuclear Power Station, including directly under the reactor building.



The Nuclear Regulation Authority continued to determine whether 10 of these were ``active faults,'' and indicated that if even one was an ``active fault,'' it would not be possible to restart operations.



In response, Hokuriku Electric Power presented data obtained using the "mineral vein method" as evidence that it was not an "active fault."



The "mineral vein method" is a method to investigate minerals distributed across the fault.