Nuclear reactors face long screening times

Nearly eight years have passed since the severe accident at Tokyo Electric Power Company Holdings, Inc.’s Fukushima No. 1 nuclear power plant in March 2011. Based on the lessons from the accident, new safety standards for nuclear power plants were implemented in July 2013, and 15 nuclear reactors at eight power plants cleared the new standards.

Of them, nine reactors at five plants have resumed operations. On the other hand, safety screenings for some reactors have been prolonged, and it has been decided that many reactors will be decommissioned.

On Jan. 27, I visited Chubu Electric Power Co.’s Hamaoka nuclear power plant in Shizuoka Prefecture, where I saw a 22-meter-high coastal levee. After the Great East Japan Earthquake, an 18-meter-high levee was constructed and subsequently heightened by four meters.

“Before the earthquake, the plant only had a sand embankment. Compared to that, we significantly enhanced countermeasures against tsunami,” said Toshihiro Kodaka, general manager of Chubu Electric Power’s Communication Planning and Public Relations Group in the Hamaoka Community Relations Office.

The Hamaoka nuclear power plant is located near the likely focuses of an anticipated Tokai or Nankai Trough earthquake. In May 2011, just after the earthquake, then Prime Minister Naoto Kan requested that the power company suspend operations at the nuclear power plant and it accepted the request; operations have been suspended ever since.

About five years have passed since the company applied for a safety screening of the plant’s No. 4 reactor, while 3½ years have passed for the No. 3 reactor.

Concerning the Nuclear Regulation Authority’s safety screenings, discussions are ongoing about how to factor in tsunami. While Chubu Electric Power assumes a tsunami of up to 21.1 meters, the NRA calls for the company to make calculations based on even harsher conditions.

On Jan. 28, I visited Tohoku Electric Power Co.’s Onagawa nuclear power plant in Miyagi Prefecture, where I saw a 29-meter-high levee that had been constructed after the disaster. The nuclear power plant was hit by tsunami of 13 meters in the wake of the earthquake. The nuclear reactor building is located on a site 14.8 meters above sea level.

While the earthquake caused the entire Ojika Peninsula, where the nuclear plant is located, to subside by 1 meter, the plant was not flooded. Since one of the external power sources remained intact, cold shutdown of all three reactors could be done by the following day.

More than five years have passed since Tohoku Electric Power applied for a safety screening of the No. 2 reactor. The design policy of the levee became a focal point during the screening. At first, Tohoku Electric Power adopted a construction method that would allow some of the piles to sink slightly in the wake of an earthquake, claiming that even though some piles would sink, it would be possible to keep a height of 29 meters.

However, due to concerns expressed by the NRA, the company decided to conduct soil improvement work so that the piles will not sink.

At an NRA screening meeting held on Jan. 15, discussions about the levee almost reached a conclusion.

“They spent more than a year on the discussion, so this is great progress,” said Kazuho Hirata, general manager at the Onagawa nuclear power plant’s Civil and Architectural Engineering Department.

Tohoku Electric Power plans to finish explanations to the NRA by July this year. The nuclear plant is expected to resume operations after fiscal 2020, when the construction of safety measures is completed.

At present, 12 reactors at eight nuclear power plants are undergoing safety screenings by the NRA. The point of focus in the screenings is basic earthquake ground motion, which corresponds to the strongest possible seismic shock.

Out of the 12 reactors, the NRA considers the assessment of basic earthquake ground motion for two reactors — the No. 2 reactor at the Onagawa nuclear power plant and the No. 2 reactor at Chugoku Electric Power Co.’s Shimane nuclear power plant — to be largely reasonable.

Safety screenings for many of the remaining 10 reactors have been prolonged due to the difficulty of proving that faults under the sites of nuclear power plants are not active, as well as for other reasons.

The NRA recognizes as “capable faults” those faults that have possibly been active within the past about 120,000 to 130,000 years. If capable faults lie directly under important facilities such as nuclear reactors, such sites are judged inadequate for building nuclear power plants, so it is impossible to operate such facilities.

As for two nuclear reactors at the Japan Atomic Power Co.’s Tsuruga Power Station and Hokuriku Electric Power Co’s Shika nuclear power plant, since the existence of capable faults is suspected there, screening for these reactors has not progressed.

Hokkaido Electric Power Co.’s Tomari nuclear power plant applied for safety screening for its Nos. 1-3 reactors 5½ years ago.

At first, the company intended to deny the possibility of the existence of capable faults under the site based on the geological age of volcanic ash strata, but it failed to find such ash. For that reason, the company last year switched to a method of evaluating the time when the faults were active from strata formed when the sea level was higher.

Akira Ishiwatari, an NRA commissioner who conducted an on-site inspection at the plant in October last year, showed a certain level of understanding, saying, “We are being convinced through explanations by Hokkaido Electric Power.”