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Tokyo Electric Power Co. (Tepco) needs to find a place to dump its radioactive sludge, which is enough to fill an Olympic-sized swimming pool.

Tepco plans to start decontaminating millions of liters of water poured over melted reactors after the March 11 earthquake and tsunami knocked out cooling systems. By the end of the year it expects to have 2,000 cubic meters of highly radioactive sludge separated from the water, said Teruaki Kobayashi, a nuclear facility manager at Tepco.

“We haven’t determined a final disposal site for the waste,” Kobayashi said. “Our priorities are decontaminating radioactive water and maintaining cooling efforts.”

Tepco has yet to say how much radiation released from the crippled reactors at the Fukushima Dai-Ichi plant in the three months since the meltdowns started. Government tests in May showed radioactive soil in pockets of areas outside a 20-kilometer (12 mile) exclusion zone around the plant have reached the same level as Chernobyl, where a “dead zone” remains since a reactor exploded in 1986.

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Radiation from the plant has spread over 600 square kilometers, according to a report by the Nuclear Waste Management Organization of Japan.

The sludge will go in tanks at the station, where three reactors melted, and moved to a temporary storage unit in December, Kobayashi said. About 105 million liters (28 million gallons) of contaminated water lies in basements and trenches at Fukushima and Tepco expects the amount to almost double by the end of the year.

The company delayed the start of operations of the decontamination unit supplied by Areva SA to June 17, Junichi Matsumoto, a general manager at Tepco, said yesterday. The delay comes about because more workers at the plant are registering dangerous levels of radiation.

The utility yesterday said six workers suffered radiation exposure exceeding the government’s annual limit of 250 millisieverts for atomic plant staff, bringing the total to eight who have crossed the threshold.

Two of the workers may have received double the 250 millisievert limit, or a level that increases the risk of cancer, according to the World Nuclear Association. The findings come from preliminary assessments of 2,367 of 3,726 people who worked at the plant in March, Junichi Matsumoto, the utility’s general manager said.

Radiation in the water is at 720,000 tera becquerels, Matsumoto said at a media briefing in Tokyo on June 3. That’s almost as much as the latest estimate of the radiation released into the air in the five days after March 11.

At Chernobyl, the world’s worst nuclear disaster, 5.2 million tera becquerels of radiation discharged, Japan’s Nuclear and Industrial Safety Agency said on April 12.

Most of the water poured over the reactors has overflowed or leaked into basements, connecting tunnels and service trenches at the plant, which has six reactors housed in separate buildings. The plant is about 220 kilometers north of Tokyo.

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