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Thursday, April 14, 2011

Radiation surges above 4's fuel pool


STAFF WRITER

Radiation has risen to high levels above the spent-fuel pool at reactor No. 4 and its temperature is rising, the nuclear safety agency said Wednesday, indicating the fuel rods have been further damaged and are emitting radioactive substances.

The radiation level 6 meters above the spent-fuel storage pool at the crippled Fukushima No. 1 nuclear plant was measured at 84 millisieverts per hour Tuesday. Normally, it's 0.1 microsievert.

The temperature of the pool was 90 degrees, compared with 84 before it caught fire on March 15 in a suspected hydrogen explosion, the agency said.

"It's quite an amount," figured Hidehiko Nishiyama, a spokesman for the Nuclear and Industrial Safety Agency.

Tokyo Electric Power Co. was unsure whether the surge in radiation was being caused by the spent fuel rods or radioactive material leaking from the reactor's pressure vessel.

Tepco used a robot to take a water sample from the pool Tuesday to analyze the radioactive materials in it, which can tell them in greater detail what is happening to the spent fuel rods.

Tepco dumped 195 tons of fresh water onto the rods early Wednesday to stop the temperature from rising.

"The temperature was rising and we don't know the water level of the pool, so we thought it would be safer to pour water," said NISA's Nishiyama said.

Tepco said it is planning to move the spent fuel rods out of the storage pools at reactors 1 through 4 so they can be moved to a safer location, although details on when and how haven't been decided yet.

Some of the options Tepco is considering include pulling the rods out with a crane or building a special structure nearby to pull them out.

But these tasks will be tough because the site is so radioactive and cluttered with debris from last month's hydrogen explosions. Meanwhile, the water level of radiation-contaminated water in the tunnel-like trench at Unit 2 dropped by 4.3 cm Wednesday morning after Tepco started pumping lethally radioactive water from its flooded turbine room into a nearby storage facility the day before.

Getting the 6,000 tons of water out is expected to take four to five days , Tepco said.

NISA also said the utility was rushing to finish installing seven steel sheets around a seawater intake for reactor 2 later in the day and silt fences near intakes for reactors 3 and 4 to hinder the spread of thousands of tons of radioactive water it dumped into the ocean.

Nishiyama also said that a seawater sample taken Monday 15 km away from the nearby city of Minamisoma, Fukushima Prefecture, showed that the concentration of radioactive iodine-131 was about 23 times the legally permissible level.

NISA said that level does not pose any health risks.

Separately, Tepco said the fuel rods in the Unit 4 pool had released cesium-134 and -137 in the process of being damaged. Cesium-137 has a half-life of 30 years. "Contaminated water leaked From the Unit 2 may have gathered as a lump and drifted offshore," Nishiyama said. "We need to continue monitoring it."

Massive amounts of water have been poured into the reactors and the spent-fuel pools as a stopgap measure to cool them down and prevent them from burning. But pools of highly contaminated water have been detected in various parts of the nuclear complex, with some of it leaking into the Pacific, as an apparent side effect of the emergency measure.

Prime Minister Naoto Kan said Tuesday that the situation of the troubled reactors is "improving step by step" and that the release of radioactive particles from the plant is declining.



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