Safety Screenings Halted at Japan Nuclear Power Plant Over Flawed Data

The Yomiuri Shimbun
Japan Nuclear Fuel Ltd. President Naohiro Masuda, left, apologizes to Nuclear Regulation Authority Chairman Shinsuke Yamanaka at an NRA meeting in Minato Ward, Tokyo, on April 14.

Safety screenings for the under-construction Oma Nuclear Power Station in Aomori Prefecture have been effectively suspended, as errors were found in safety assessment documents that operator Electric Power Development Co. (J-Power) submitted to the Nuclear Regulation Authority, it has been learned.

According to sources, a figure that should have been in kilometers was mistakenly input in meters, in calculations related to the seismic design for the plant. The documents therefore included erroneous information that was significantly different from the actual data.

When calculating the seismic motions caused by a fault around the plant, a company that J-Power commissioned to analyze data erroneously input the depth from the ground’s surface to the top of the fault as 3 meters instead of 3 kilometers.

Due to the error, it had been assumed that the Oma plant was at risk of being hit by larger tremors than it actually is. J-Power reported the flaws to a screening meeting of the nuclear watchdog in February.

As J-Power is currently devising measures to prevent such a mistake from happening again, the NRA has been unable to conduct screenings on the fault, the sources said.

J-Power was supposed to check the data provided by its contractor but missed the errors. The company had 14 opportunities to inspect the data, according to the sources.

The NRA questioned the accuracy of the data in the documents and had asked J-Power for confirmation twice since last year. However, the company denied the mistakes and failed to notice them sooner.

The Oma nuclear power plant will be one of the largest in Japan, with an output of 1.38 million kilowatts. Construction started in 2008. J-Power applied for safety screenings in 2014 based on new regulatory standards introduced after the accident at the Fukushima No. 1 nuclear power plant operated by Tokyo Electric Power Company Holdings, Inc., with the aim to start the Oma plant’s operation in fiscal 2030.

Errors delay reactors’ restart

During the NRA’s screening meeting in February, one examiner after another criticized the flaws in the documents. “This is an extremely serious matter, creating a major obstacle to the screenings, which were supposed to be conducted based on accurate data,” one person said.

Hiroyasu Sugiyama, an executive vice president of J-Power, repeatedly apologized in response.

Other companies also have made errors in documents submitted for safety screenings.

Regarding the No. 2 reactor of Japan Atomic Power Co.’s Tsuruga Power Station in Fukui Prefecture, more than 1,300 errors were found in data on fault lines within the plant site. In April, the NRA suspended its safety screenings and took the rare step of issuing an administrative directive to the company calling for it to submit corrected documents.

Omissions, missing pages and other flaws were found in about 3,100 pages of an about 60,000-page report during screenings for Japan Nuclear Fuel Ltd.’s reprocessing plant in Aomori Prefecture. In April, the NRA called on the company’s management to prevent a recurrence.

In the wake of the accident at the Fukushima No. 1 nuclear power plant in 2011, a declining number of people have wanted to work in the nuclear power industry. If progress is not made on restarting offline nuclear reactors, the knowledge and technology required to safely operate nuclear power plants will not be passed on, affecting the development of young human resources in the industry.

This could create a vicious cycle that will make it difficult to utilize nuclear power plants in the future.