Fukushima: Il reattore 2 incontrollabile, radiazioni 10 milioni di volte superiori alla norma

domenica, 27 Marzo, 2011

Ecco il quadro fornito poco fa dall’agenzia Kyodo News (ore 12,30 italiane).

TOKYO, March 27, Kyodo

Japan on Sunday faced an increasing challenge of removing highly radioactive water found inside buildings near some troubled nuclear reactors at the Fukushima Daiichi plant, with the radiation level of the surface of the pool in the basement of the No. 2 reactor’s turbine building found to be more than 1,000 millisieverts per hour.

The concentration level is 10 million times higher than that seen usually in water in a reactor core, according to plant operator Tokyo Electric Power Co. Hidehiko Nishiyama, spokesman for the government’s nuclear safety agency, said the figure is ”quite high” and ”likely to be coming from the reactor.”

Adding to woes is the increasing level of contamination in the sea near the plant. Radioactive iodine-131 at a concentration 1,850.5 times the legal limit was detected from water extracted Saturday afternoon, compared with 1,250.8 times the limit found Friday, the agency said.

Nishiyama said he cannot deny the possibility that radioactive materials are continuing to be released into the sea, although it is not clear from what route, but he reassured that there is no need for health concerns so far.

The pools of water containing radioactive substances have drawn attention after three workers who were engaging in work to restore the No. 3 reactor at its turbine building on Thursday were exposed to high radiation. Two of them had their feet in water without noticing then that it was highly contaminated.

The radioactivity at the surface of the puddle at the No. 3 unit was 400 millisieverts per hour.

The three workers, who had been taken to a radiation research center in Chiba Prefecture for examination, would be discharged as early as Monday afternoon, officials of the center said, adding that the exposure has not affected their health.

According to the latest data released Sunday, radioactive iodine-134, a substance which sees its radiation release reduced to about half in some 53 minutes, existed in water at the No. 2 reactor’s turbine building at an extremely high concentration of 2.9 billion becquerels per 1 cubic centimeter.

The water also contained such substances as iodine-131 and cesium-137, known as products of nuclear fission, and thus leading to speculation that it may have come through pipes that connect the reactor vessel and turbines, where steam from the reactor is normally directed to for electricity generation.

The pool of water at the No. 4 reactor’s turbine building included radioactive substances, but the concentration level was not as high as at the Nos. 1, 2 and 3 buildings, the data showed.

Following the March 11 massive earthquake and tsunami, the reactors and the spent nuclear fuel tanks of the Nos. 1, 2 and 3 units lost their cooling functions. Their reactor cores also partially melted at the plant, possibly discharging radioactive substances.

The No. 4 unit, meanwhile, had all of its fuel rods stored in the spent fuel tank for maintenance work, and the cooling functions of the tank were also lost.

To cool down the reactor cores or spent fuel tanks, massive amounts of seawater or freshwater have been injected such as by spraying water from outside the damaged part of the reactor buildings’ outer shell.

Tokyo Electric is continuing efforts to restore power and enhance cooling efficiency at the crisis-hit nuclear power plant, but the highly radioactive pools of water are slowing the progress of the restoration work.

Workers there are planning to turn on the lights in the control room of the No. 4 reactor, while also trying to inject fresh water into tanks storing spent nuclear fuels at the plant’s Nos. 1, 2, 3 and 4 reactors to prevent crystallized salt from seawater already injected from hampering the smooth circulation of water and thus diminishing the cooling effect.

The company will also try to inject fresh water into the Nos. 1, 2 and 3 reactors using electrical pumps instead of fire pumps currently used.

Electrical pumps enable workers to spend less time and energy operating the machines at the site, thus reducing the risk.

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