TOKYO — Tokyo Electric Power found a new radioactive leak at the wrecked Fukushima nuclear plant over the weekend, capping its worst month since the March 2011 earthquake and tsunami caused reactors to meltdown.
The utility, known as Tepco, said Sunday it had halted a contaminated water leak from a pipe, near an area of high radiation levels discovered on Saturday. Of the four hot spots found, one recorded radiation of 1,800 millisieverts per hour around the bottom of a bolted-flange tank storing water used to cool melted reactor cores. That’s 18 times the level reported at the same spot on Aug. 22, Tepco said. It would be a lethal dose after four hours of exposure.
With more than 338,000 metric tons of water with varying levels of toxicity stored in pits, basements and hundreds of tanks at the Fukushima plant, Tepco has been overwhelmed in trying to contain leaks. Prime Minister Shinzo Abe said Tepco isn’t able to handle the disaster recovery after the company revealed a separate discharge of as much as 300 tons of irradiated water into the ocean each day.
Tepco should speed up installation of welded storage tanks to stop the leaks at the damaged nuclear plant, Tetsuo Ito, head of Kinki University’s Atomic Energy Research Institute, said in a phone interview Sunday.
In the rush to find storage for the tens of thousands of tons of radioactive water in the plant, Tepco used some tanks with bolted flanges sealed by resin rather than welds. Resins swell and contract as temperatures fluctuate, which can lead to leaks, said Ito.
“Tepco hasn’t been reliable looking after issues at Fukushima,” Ito said. “It’s not too late. Going forward they must install proper tanks and move the contaminated water out of those bolted tanks.”
Radiation levels Tepco disclosed at the weekend don’t raise an immediate concern for the general public because the site is off limits, Ito said. Case studies in Hiroshima and Nagasaki showed that direct exposure to 1,800 millisieverts for four hours can be lethal, he said.
“It’s not life-threatening, as Tepco’s inspectors don’t stay in one spot for four hours,” he said. “But the situation can’t be left as it is.”
Tepco said the 1,800 millisieverts reading was found 5 centimeters above the area that was checked, falling to 15 millisieverts at 50 centimeters. The reading was for beta radiation that travels short distances and can be blocked by use of metal sheet such as aluminum, the company said on its website.
The leaking pipe, which was attached to another storage tank, was dripping water at a rate of about one drop every 90 seconds, Tepco said in a statement Sunday. The utility said Saturday that it had found radiation of 230 millisieverts per hour in the same area as the tank.
The weekend radiation spike capped a particularly embarrassing month for the utility in its more than two year struggle to contain the disaster, the worst civilian nuclear accident since Chernobyl.
Japan’s Nuclear Regulation Authority called another storage tank leak last month, first estimated at 300 tons of highly radioactive water, the most serious since the original disaster, before it said it might have to reconsider its conclusion when it found Tepco hadn’t kept records of how much water was in the tank.
Shunichi Tanaka, chairman of the regulator, told reporters in Tokyo on Wednesday that since there was no gauge on the tank, there was no idea about the size of the leak.
Growing frustration with Tokyo Electric’s management of the site surfaced when Shinji Kinjo, leader of a disaster task force at the regulator, said Tepco was careless in checking 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 and is now the largest pool of radioactive water in the history of nuclear accidents, is raising concerns among nuclear engineers around the world. Tepco finds itself in a King Canute-like challenge, trying to turn back a growing tide of toxic water and getting overwhelmed.
What’s more, Tepco needs to start thinking beyond storage to getting rid of the water, engineers say.
Processing and disposing of the water, enough to fill a very large crude oil tanker, will be one of the most challenging engineering tasks of our generation, former nuclear engineer Michael Friedlander said.
“There are really only a few ways you can get rid of it,” Friedlander said. “You put it in the ocean or it’s going to have to be evaporated. It’s a political hotspot, but at some point you cannot just continue collecting this water.”
Japan’s government said last month it will take a bigger role in staunching the toxic outflow that’s grown to 40 times the volume accumulated in the atomic disaster at Three Mile Island in the U.S.
Tepco has yet to decide how to dispose of the contaminated water, spokeswoman Mayumi Yoshida said last week. It will need approval from the government, local residents and fishermen before it can act, she said.