JAPAN | Stable operation of Fukushima plant top priority before lifting evacuation zones

Posted on August 4, 2011

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JAPAN | MAINICHI | 4 August 2011

In this June 12, 2011 photo released on July 5, 2011 by Tokyo Electric Power Co., masked workers in protective outfits prepare to drop one of sliding concrete slabs into a slit of the upper part of the sluice screen for Unit 2 reactor at the tsunami-crippled Fukushima Dai-ichi nuclear power plant in Okuma, Fukushima Prefecture, northeastern Japan, in their effort to decrease the leak of radiation contaminated water to the ocean. (AP Photo/Tokyo Electric Power Co.)

Stable operation of the crippled Fukushima No. 1 Nuclear Power Plant’s system to purify contaminated water will determine whether or not the current crisis can be brought under control and is one of the conditions for lifting emergency evacuation preparatory zones some 20 to 30 kilometers from the plant.

“If temperatures in nuclear reactors drop below 100 degrees Celsius to reach a state of cold shutdown, vapor generation including radioactive substances will be restrained, and we can expect a further decline in the dosage rate in the air around the plant,” said Tadashi Narabayashi, a professor of reactor engineering at Hokkaido University.

Tokyo Electric Power Co. (TEPCO) estimates that radiation doses at the plant’s boundary would reach a maximum 1.7 millisieverts on the premise that the entire amount of radiation monitored from June 20-28 had been released from the plant’s nuclear reactor buildings.

TEPCO and the government aim to lower the dose of radiation to less than one millisievert by early next year following the completion of step 2 (three to six months from mid-July) under a road map to bring the crisis under control.

As of Aug. 1, temperatures at the bottom of the pressure vessel stood at 93 Celsius at the No. 1 reactor, 121 Celsius at the No. 2 reactor and 106 Celsius at the No. 3 reactor. In order to reduce vapor from the reactor cores, the amount of water pumped into the No. 2 and No. 3 nuclear reactors has to be increased to bring temperatures there to less than 100 Celsius.

In this photo released by Tokyo Electric Power Co. (TEPCO), a small fire breaks out from facilities sampling seawater located a few dozen meters from Unit 4 inside the tsunami-crippled Fukushima Dai-ichi nuclear power plant in Okumamachi, Fukushima Prefecture, northeastern Japan, Tuesday morning, April 12, 2011. The fire was put out soon and the ongoing cooling operations at the main units were not affected according to TEPCO. (AP Photo/Tokyo Electric Power Co.)

In this photo released by Tokyo Electric Power Co. (TEPCO), a small fire breaks out from facilities sampling seawater located a few dozen meters from Unit 4 inside the tsunami-crippled Fukushima Dai-ichi nuclear power plant in Okumamachi, Fukushima Prefecture, northeastern Japan, Tuesday morning, April 12, 2011. The fire was put out soon and the ongoing cooling operations at the main units were not affected according to TEPCO. (AP Photo/Tokyo Electric Power Co.)

But TEPCO is having difficulty in stably operating the plant’s cleanup system. And contaminated water is rising, forcing the utility to restrict water injections to stop contaminated water from increasing further.

“To ensure stable operations of the plant’s cleanup system, it is essential to pump water into the reactors without worrying about an increase in contaminated water. If the temperatures are reduced to less than 100 Celsius, the radiation dose along the plant border may be cut to the target of one millisievert a year,” said a senior official of the Nuclear and Industrial Safety Agency.

Haruki Madarame, chairman of the Nuclear Safety Commission of Japan, said at a news conference on Aug. 7 that stable operations of the water purification system are the biggest challenge. He said the amount of radioactive materials spewing from the nuclear reactors will help determine if the emergency evacuation preparatory zones will be lifted.

The government will enter into talks as early as later this month with local governments concerned on removing the emergency evacuation zones.

Narabayashi said, “A cold shutdown should be realized as soon as possible by giving priority to Fukushima evacuees. Multiple systems should be studied instead of the current single route to prevent the cleanup system’s operating rate from falling.”

In this photo taken on Thursday, March 31, 2011 by Japan Maritime Self-Defense Force and released by Japan Defense Ministry Friday, April 1, a U.S. military barge carrying pure water arrives to the quay near Unit 1 of the tsunami-stricken Fukushima Dai-ichi nuclear complex in Okumamachi, Fukushima Prefecture, northeastern Japan, after being towed by a JMSDF tugboat, not shown. (AP Photo/Japan Defense Ministry)

In this photo taken on Thursday, March 31, 2011 by Japan Maritime Self-Defense Force and released by Japan Defense Ministry Friday, April 1, a U.S. military barge carrying pure water arrives to the quay near Unit 1 of the tsunami-stricken Fukushima Dai-ichi nuclear complex in Okumamachi, Fukushima Prefecture, northeastern Japan, after being towed by a JMSDF tugboat, not shown. (AP Photo/Japan Defense Ministry)

TEPCO on Aug. 3 submitted to the Nuclear and Industrial Safety Agency a plan to install a cesium absorption unit called SARRY made by Toshiba Corp. and other parties to back up the current cleanup equipment.

TEPCO will launch this double track program as early as mid-August.

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