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Wednesday, May 18, 2011

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Finally there: After being towed for weeks from Shizuoka, a "megafloat" docks at Onahama port in Iwaki, Fukushima Prefecture, on Tuesday. The huge container will be used to store irradiated water from the Fukushima No. 1 nuclear plant. KYODO

Plan to cool reactors revised but not timeline

Damage to reactor vessels leads to alterations of earlier road map


By KAZUAKI NAGATA and MINORU MATSUTANI
Staff writers

Tokyo Electric Power Co., facing more problems at the Fukushima No. 1 nuclear power plant than it originally thought, announced Tuesday a revised road map for bringing the crisis under control.

A major change from the first plan released a month ago will be using a massive amount of irradiated water flooding the basements of the turbine buildings for reactors 1, 2 and 3 as a main circulating coolant.

The original plan called for flooding the containment vessels to cool the reactor cores, but the level of the water in reactor 1's containment vessel doesn't appear to be increasing despite an injection of more than 10,000 tons of water.

Because the containment vessels of reactors 2 and 3 are also possibly damaged, Tepco has given up on the flooding method for now, although it may do it again if the utility can find and plug cracks and holes in their containment vessels.

Tepco said it will still stick to its time frame of aiming to achieve a cold shutdown of reactors 1, 2 and 3 and bring the temperature of the reactor-core coolants below 100 degrees in five to eight months.

Nuclear experts immediately greeted the revised plan with skepticism.

"I think it will be very difficult" to achieve the plan in that time frame, said Tsuyoshi Misawa, a reactor physics and engineering professor at Kyoto University's Research Reactor Institute.

He said the definition of a "cold shutdown" is now ambiguous, as the reactor cores of units 1, 2 and 3 have probably melted and fallen down to the bottoms of the pressure vessels. If the fuel rods have melted and become mushy, the inside could get extremely hot even if the temperature of the surface is kept low.

The road map is basically divided in two phases. The first phase will take about three months, or until mid-July, to get the reactor cores cooled on a consistent basis and reduce the amount of radioactive material leakage.

The second step is expected to take up to six months to achieve the cold shutdown and control the leakage drastically after the first step has been completed.

Misawa pointed out that the most important work will be to identify cracks and holes and then plug them to prevent the radioactive water leaking outside the reactors and their buildings.

"But that work doesn't seem to be progressing at all," he said.

Announcing the updated road map at a news conference, Tepco Vice President Sakae Muto said some things have gone well in the past month, while some things have not.

"Overall, I think we are following the schedule to complete phase one," he said, although he did not comment on what percentage of the work has been completed.

From the very beginning, some experts have branded the Tepco road map as overly optomistic because there are too many uncertainties, such as how the utility will be able to plug the cracks in the damaged pressure vessels, as humans can't get near the site due to the high level of radiation.

Tepco admitted that a large part of the core of the No. 1 reactor has probably melted and fallen down to the bottom of the pressure vessel, and that the same may be true for reactors 2 and 3.

Asked if the melting of the reactor core affects the road map, Muto said it doesn't affect the plan, as the most important thing is to keep cooling the core.

The plan includes measures to process radioactive water in the basement of the turbine buildings and underground trenches, and to prevent contamination of the underground water.

Tepco is building a new water processing facility that can process 1,200 tons a day.

Tepco says the 87,500 tons of radioactive water currently flooding the plant ~~~- which is increasing daily—can be processed by the end of the year the new facility starts operating.

The firm also said it will improve the environment for the workers at the site by providing better food and more rest facilities, as conditions will grow more harsh with summer approaching.

The plan includes controlling and reducing the radiation leaks in five to eight months with measures like covering the reactor buildings with polyester sheets.



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