Tokyo Electric Power Company is looking into the possibility that untreated water leakage from a filtering device at Fukushima Daiichi power plant was because workers may have forgotten to shut some of the valves.
The company, known as TEPCO, said earlier that about 5.5 tons of water that contained radioactive substances leaked to the environment through an outside vent of the filtering device on Wednesday morning. The leakage occurred while workers were washing inside of the pipes installed on the filtering device.
TEPCO said that the leaked water contained an estimated 22 billion becquerels of cesium-137 and other substances that emit gamma rays. The figure far exceeds the minimum of 100 million becquerels, which is the standard level for reporting to the government.
TEPCO said that at around the time the leakage was discovered, a dust monitor that measures atmospheric levels of radioactive substances above the plant temporarily showed a slight increase in data. It says the figure has now returned back to normal.
The utility also pointed out that it has not detected any significant changes in levels of radioactivity around the power plant measured at monitoring posts, and at monitoring devices for nearby drainage canals.
TEPCO explained on Thursday that the pipes which the workers were washing when the leak occurred have 16 valves that are operated by hand.
The firm said these valves are opened during the work and are shut again manually after the work is complete, but 10 of them were left open, resulting in the leakage.
TEPCO said that it is investigating the possibility that workers had mistakenly forgotten to shut the valves.
On Thursday afternoon, TEPCO started work to remove the soil which the leaked water is believed to have seeped into.
Fukushima Prefecture has said the leakage of untreated water is extremely regrettable. The head of its crisis management section, Watanabe Jin, summoned the head of the power plant, Taminami Tatsuya, on Thursday.
Watanabe requested that TEPCO should conduct a rigorous investigation to make sure that there will never be an accident like this in future. He also urged the firm to keep local residents well-informed about environmental impacts and what it plans to do to prevent a recurrence.
Taminami said TEPCO is taking the latest leakage extremely seriously. He said the company will analyze what led to the problem, and take thorough measures to ensure that there will never again be a leakage like this.