Tokyo Electric Power Co.’s inexact monitoring of contaminated water stored at the Fukushima atomic plant may have led the utility to overstate last week’s storage tank leak, according to Japan’s nuclear regulator.
The 300-metric-ton loss reported by the utility known as Tepco was based on an assumption that the tank had been full before the leak, Shunichi Tanaka, chairman of Japan’s Nuclear Regulation Authority, told reporters yesterday in Tokyo. That assumption may not have been reliable, since there was no gauge measuring the individual tank’s water level, he said.
“We have no idea whether it’s actually 300 tons that leaked,” Tanaka said. “We need to look into this issue more.”
Tokyo Electric’s management of contaminated water at the Fukushima plant has already drawn fire from Shinji Kinjo, leader of a disaster task force at the NRA, who has said the utility was careless in its monitoring of the storage tanks and failed to keep records of its inspections.
Managing the water, which is increasing at a rate of 400 tons a day, is a fundamental challenge for Tepco as it struggles with the cleanup of the Fukushima Dai-Ichi plant, a process that could take as long as 40 years.
Tepco’s shares fell 2.6 percent to 497 yen at the close of Tokyo trading. The Nikkei 225 Stock Average rose 0.9 percent.
Tanaka’s remarks yesterday came hours after the NRA said it had finalized its ranking of the leak, based on Tepco’s reckoning, as a level 3 “serious incident” on the seven-stage International Nuclear and Radiological Event Scale, or INES, its worst assessment of the problems at Fukushima since the earthquake and tsunami of 2011 caused reactors to melt down.
The NRA may reconsider its INES ranking should further studies show different amounts of water loss than those provided by Tepco, Tanaka said.
“It’s up to us to provide accurate data to the nation,” he said.
The leak may have begun some time in July, Mayumi Yoshida, a Tepco spokeswoman, said yesterday. Tepco characterized the leak as small when it was first detected on Aug. 19, prompting the NRA to designate it a 1, or an “anomaly,” on the INES scale.
The higher ranking was assigned after Tepco determined by the change in the tank’s water level that 300 tons of contaminated water had escaped.
The International Atomic Energy Agency said in a statement posted on the NRA website yesterday that the Japanese agency should explain why last week’s leak merited an INES rating while previous incidents did not.
The leak was the fifth and largest storage tank spill since January 2012, according to Tepco, which also stopped using underground basins to store water after several leaks were found in April 2013.
The IAEA also advised the NRA to communicate the severity of plant incidents more clearly and to avoid confusing the public with upgrades and downgrades.
“Frequent changes in rating will not help to communicate the actual situation in a clear manner,” the IAEA said in the statement.
David Lochbaum, the director of the Union of Concerned Scientists in the U.S., faulted the NRA for only responding to safety problems rather than working to avoid those lapses.
“A good regulator does not wait for bad things to happen and then write tickets for the offenses,” Lochbaum said in an e-mail. “A good regulator monitors activities and ensures that there are multiple barriers in place each with sufficient reliability to reduce the chances that all barriers fail to a very small number.”
Another of Tepco’s challenges was highlighted yesterday when Niigata Governor Hirohiko Izumida said he would continue to resist the restart of the company’s Kashiwazaki-Kariwa nuclear power plant, which is located in his prefecture.
“There remain concerns about whether safe operations are possible or not,” said Izumida, who also accused the NRA of adopting too narrow a mission that neglects the safety of local residents.
Izumida’s approval is critical before Tepco can go ahead with plans for the restart of Kashiwazaki-Kariwa, the world’s largest nuclear power station by generating capacity.
The governor of Fukushima, who was also in Tokyo yesterday to meet with Trade Minister Toshimitsu Motegi, asked that Tepco be strictly monitored by the government as it pursues the cleanup. Governor Yuhei Sato also asked for a review of ocean monitoring done by Tepco and the government.
Motegi said during an Aug. 26 visit to the plant that the government would assume leadership of the utility’s water-management efforts.