Japan's nuclear regulators have admitted poor management was responsible for the worst leak of toxic water in six months at a crippled nuclear plant.
Tokyo Electric Power Co was criticised for insufficient crisis management after the leak of about 100 tons of radioactive water from a storage tank at the Fukushima Daiichi nuclear plant last week, Tokyo Shimbun newspaper reported.
The leak was attributed to an improper valve setting, which led to the tank overflowing with contaminated water, and the lack of an alarm warning of a rise in water levels.
Tokyo Electric officials conceded on Tuesday that workers at a control room had failed to notice the problem soon enough.
"The failure to check the water level of the tanks that should have been receiving water was a problem from the viewpoint of preventing the situation from worsening," Nuclear Regulation Authority commissioner Toyoshi Fuketa said.
The leak was the largest since about 300 tons of toxic water escaped from another storage tank in August. Three reactors at the plant suffered meltdowns after a March 2011 earthquake and tsunami.
The operator is injecting water into the reactors to keep them cool and has been battling leaks from storage containers where the resulting radioactive water is being stored.
On Tuesday a cooling system failure at reactor 4 prompted the operator to temporarily suspend the removal of spent nuclear fuel rods at the unit.
Workers damaged a cable during excavation near the electrical equipment in the morning, Tokyo Electric said. The cooling system was working again by the afternoon.
The water temperature in the pool remained below the operational limit of 65 degrees, the operator said.
Tokyo Electric began removing more than 1500 nuclear fuel rod assemblies at the reactor in November.
