Japan’s nuclear watchdog concluded that the No. 2 reactor at the Tsuruga nuclear power plant in Fukui Prefecture does not comply with regulatory safety standards due to fears of an active fault running directly under the facility.

The assessment by the Nuclear Regulation Authority will likely put the kibosh on restarting the plant operated by Japan Atomic Power Co., although a formal decision will be announced later.

Japan Atomic Power will be forced to consider decommissioning the facility if the application to restart the reactor is denied.

The operator plans to seek further reviews from the NRA after additional plant surveys to secure permission to restart the reactor.

The No. 2 reactor, which went into operation in 1987, has an output of 1.16 million kilowatts.

It would mark the first time for the NRA, set up in 2012 following the Fukushima disaster, to reject an application to restart a reactor under the new rules.

Improved safety regulations drawn up after the Fukushima disaster prohibit operating nuclear power plants if an active fault is known to be running directly under critical facilities such as reactor buildings.

The NRA mandates that electric power companies must prove scientifically that there are no active faults during the examination process for restarting nuclear power plants.

The focus of the review was whether the “K fault” found in a trench about 300 meters north of the reactor is active or not, and whether it extends directly under the reactor building.

Japan Atomic Power asserted that the K fault is not active, citing strata analysis and a boring survey conducted south of the K fault, which it said had not confirmed a fault similar to the K fault or that it extended directly under the reactor building.

But the NRA dismissed the claim as “lacking scientific or a technical basis.”

During the review meeting, Japan Atomic Power requested that a new investigation be added to the company’s application for a restart.

Mamoru Muramatsu, the company president, told reporters the company hopes to “make a readjustment after conducting an additional investigation.”

Muramatsu said Japan Atomic Power is not thinking about decommissioning the plant.

The NRA will discuss whether to include the additional investigation requested by the operator as a factor in its decision.

But it is unlikely the NRA will approve Japan Atomic Power’s request because it has not yet decided on the content of the additional investigation. The NRA has indicated it will make a decision based on the content of the application already filed.

The existence of an active fault at the Tsuruga plant was pointed out nearly two decades ago.

In 2008, based on a revision of the central government’s earthquake resistance guidelines, the operator recognized the “Urasoko fault” located about 200 meters from the No. 2 reactor as an active one from about 4,000 years ago.

Both in May 2013 and in March 2015, the NRA’s panel of experts pointed out that the fault directly below the reactor is an active one.

But in November 2015, the operator applied to the NRA for a review to restart the operation, claiming that “evidence had been obtained that the fault is not active.”

Of the 27 reactors in Japan that have so far applied to have their operations restarted, 17 gained approval after being found in compliance of the new regulatory standards.

Japan Atomic Power was established in 1957 as a company specializing in nuclear power generation.

In 1966, it began operation of Japan’s first commercial nuclear power plant, the Tokai nuclear power plant. The plant is currently undergoing decommissioning.

In 2015, it was decided to decommission the No. 1 reactor of the Tsuruga plant.

The company earns revenue by supplying electricity it produces to the five major electric power companies.

Tsuruga’s No. 2 reactor, along with the Tokai No. 2 nuclear power plant in Ibaraki Prefecture, are currently the two wings of Japan Atomic Power.

Both have remained shut down since the Fukushima disaster.

The company receives “basic fees” from the five utilities to cover maintenance costs of the two facilities.

Basic fees account for more than 90 percent of the 96.7 billion yen ($629 million) in the company’s sales in fiscal 2023.

If the No. 2 reactor at Tsuruga is decommissioned, a large portion of the company’s income could be lost. And it could also hinder the progress of No. 3 and No. 4 reactors at the Tsuruga plant, which are still in the planning stages.

A shakeup in the company’s business foundation could affect the restart of the Tokai No. 2 nuclear power plant, too.

(This article was written by Fumi Yada, Keitaro Fukuchi, Jumpei Miura and Tomoki Morishita.)