TOKYO — Six cleanup workers at the wrecked Fukushima nuclear plant were exposed to radiation after a hose piping contaminated water was mistakenly detached leaking seven metric tons, operator Tokyo Electric Power Co. said.
Four of the workers were contaminated during the initial spill, which was contained by a barrier around the desalination facility, Mayumi Yoshida, a spokeswoman for the utility known as Tepco, said Wednesday. Another two workers came in contact with the water when they arrived to help.
The leak is the third mishap in two weeks attributed to worker mistakes at the plant. A pump used to cool the plant’s No. 1 reactor briefly stopped Monday after a worker mistakenly pushed a stop button on the device, according to the Nuclear Regulation Authority. A miscalculation by cleanup crews is thought to have allowed a tank holding contaminated water to overflow on Oct. 3, Tepco said.
Tepco is measuring the degree of radiation exposure to the workers, who were wearing protective clothing and are not thought to have inhaled any contaminants, Yoshida said.
The amount of the leak was seven tons, Tepco said in a statement Wednesday.
The leaked water was found to have beta radiation levels of 34 million becquerels per liter, Tepco said. Beta radiation includes strontium-90, which has been linked to causing cancers such as leukemia.
Also Wednesday, Tepco released details of its investigation into the August leak of 300 metric tons of contaminated water from a storage tank, concluding the accident was probably caused by corrosion around faulty seals.
The water appears to have escaped through metal corroded by water that seeped in between two of the plates that make up the walls of the tank, Yoshida said. The leak, first detected on Aug. 19, was described by Japan’s nuclear regulator as the worst accident at Fukushima since the earthquake and tsunami of 2011 caused reactors to melt.
The plant has more than 1,000 tanks holding in excess of 380,000 tons of water irradiated from contact with reactor fuel. About 300 of the tanks are of the same bolted variety as the leaking tank. That leak may have been going on for several weeks before it was detected, Tepco has said.
The August leak was among a series of mishaps this summer that prompted Japan’s government to intensify its involvement in the site’s management after concluding responses by the utility hadn’t been adequate.