The Tokyo Electric Power Com. (TEPCO) -- the company still nominally in charge of the Fukushima Daiichi nuclear power plant -- announced Tuesday that at least 300 metric tons of highly radioactive water had leaked from storage tanks around the crippled reactor complex. Three hundred tons is roughly equivalent to the amount of water used each day by 200 U.S. families, according to the Environmental Protection Agency.
The leak is the worst yet reported and comes within weeks of numerous other revelations about the extent of radioactive contamination in the water and ground around the facility, which was severely damaged by the massive earthquake and tsunami that struck northern Japan in March 2011.
TEPCO said the contaminated water leaked from a steel storage tank on the Daiichi grounds, but added it has not determined how or where. Company spokesman Masayuki Ono said the leaking water had seeped into the ground after breaching piles of sandbags added to a concrete barrier erected around the tank. Workers were now draining the puddle and transferring the remaining water in the suspect tank to other containers.
The radiation level of the leak, measured at about two feet above the puddle, was about 100 millisieverts per hour -- five times the yearly maximum exposure for plant workers, Ono said.
Four tanks of similar design have sprung leaks in the past year.
Damage to the containment buildings and cooling systems has made it necessary to continuously pump water over the damaged reactor cores since early in the crisis. More than 1,000 tanks were built around the plant to store the massive amounts of contaminated water coming from the three melted reactor cores, as well as groundwater seeping into the structures' basements. TEPCO reports that to date, 85 percent of their tank capacity has been used.
The latest discovery comes just days after TEPCO admitted that as much as 300 tons of contaminated water per day were leaking from the reactors into the sea.
Last week, plant operators found that Fukushima workers had been exposed to radioactive water from a mist sprayer used to cool staff during hot summer days.
Prime Minister Shinzo Abe has called the leaking water an "urgent issue," and the country's Nuclear Regulatory Agency told Reuters that the situation was an "emergency."
Contaminated water has been found to contain radioactive isotopes such as tritium, strontium-90 and cesium-137. Elevated exposure to these isotopes has been linked to a number of cancers, birth defects, thyroid disease and immunological disorders.
Gregg Levine contributed to this report. With Al Jazeera and wire services