The operator of Japan's crippled Fukushima nuclear plant said on Thursday another tank holding highly contaminated water overflowed, probably sending the liquid into the Pacific Ocean, in the second such breach in less than two months.
Recent site mishaps have returned Tokyo Electric Power Co , or Tepco, to the spotlight, calling into question its ability to execute a complex cleanup that could last decades. The company has vowed to monitor the tanks more closely and improve its water management.
Amid mounting international alarm, Japan's government stepped in last month and said it would fund efforts to improvement water management at the plant.
The latest leaks show Tepco's efforts to improve its handling of the contaminated water are not sufficient, Japan's top government spokesman, Yoshihide Suga, told reporters on Thursday. The government will take steps to deal with the water, he said, adding that he thought the situation was under control.
Tepco has been relying on hastily built tanks to hold excess cooling water flushed over damaged reactors at the Fukushima Daiichi site, where three units suffered nuclear meltdowns and hydrogen explosions after a March 2011 earthquake and tsunami.
Tepco said the water that leaked contained 200,000 becquerels per litre of beta-emitting radioactive isotopes, including strontium 90. The legal limit for strontium 90 is 30 becquerels per litre.
The breach was discovered in a tank holding area away from where 300 tonnes of toxic water escaped in August.
About 430 litres (113 gallons) of water spilled over a period of as much as 12 hours after a worker misjudged how much could be held by the tank, which is tilting because of an uneven location, Tepco spokesman Masayuki Ono told reporters.
The company is filling tanks to the brim as it does not have the capacity to accommodate the buildup of contaminated water, Ono said, adding that the water is likely to have flowed into a trench leading to the Pacific Ocean, about 300 m (330 yards) from the tank.
It is also pumping out accumulated rainwater in tank holding areas.
After repeated denials, Tepco admitted in July that contaminated water was flowing into the Pacific Ocean from the wrecked reactor buildings at Fukushima.
Measurable radiation from water leaking from the facility is mostly confined to the harbour around the plant, officials have said, and is not an environmental threat to other countries as the radiation will be diluted by the sea.
Tepco has been pumping hundreds of tonnes of water a day over the Fukushima reactors to keep them cool and storing the radioactive wastewater in tanks above ground.
It has also found high levels of radiation just above the ground near other tanks, suggesting widespread structural problems with the tanks.