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28 March 2011

Woes deepen over radioactive water at nuke plant, sea contamination

Handout photo shows the No. 3 reactor, emitting smoke-like fumes, of the Fukushima Daiichi nuclear power plant in Fukushima Prefecture on March 27, 2011. (Photo taken and supplied by the Ground Self-Defense Force)(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.

Exposure to such an environment for four hours would raise the risk of dying in 30 days. Hidehiko Nishiyama, spokesman for the government's nuclear safety agency, said the figure is ''quite high'' but authorities must find a way to pump out the water without sending workers too close to push ahead with the restoration work.

Plant operator Tokyo Electric Power Co. said early Monday the concentration of radioactive substances of the puddle was 100,000 times higher than that usually measured in water in a reactor core, correcting its earlier analysis of 10 million times higher.

Adding to the woes is the increasing level of contamination in the sea near the plant, although Nishiyama reiterated there is no need for health concerns so far because fishing would not be conducted in the evacuation-designated area within 20 kilometers of the plant and radioactive materials ''will be significantly diluted'' by the time they are consumed by marine species and then by people.

Radioactive iodine-131 at a concentration 1,850.5 times the legal limit was detected in a seawater sample taken Saturday around 330 meters south of the plant, near a drainage outlet of the four troubled reactors, compared with 1,250.8 times the limit found Friday, the agency said.

Nishiyama told a press conference in the morning that he cannot deny the possibility that radioactive materials are continuing to be released into the sea. He said later that the water found at the basement of the turbine buildings is unlikely to have flowed into the sea, causing contamination.

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

Radioactivity at the surface of the puddle at the No. 3 unit was 400 millisieverts per hour as of Thursday, still far below the more than 1,000 millisieverts per hour detected at the puddle of the No. 2 reactor's turbine building.

Tokyo Electric was not able to confirm how much the actual amount of radiation was at the No. 2 reactor because the radioactivity level was too high for workers to continue measuring.

At a radiation level of 1,000 millisieverts per hour, people could suffer a decrease in the number of lymphocytes -- a type of white blood cell -- in just 30 minutes, and half of the people could die within 30 days by staying in such conditions for four hours.

According to initial data released Sunday, Tokyo Electric said 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 cubic centimeter.

But the utility said early Monday it was not able to detect the iodine-134 after reexamining the data. The company said, however, that there was no change in the fact that the water contained such substances as iodine-131 and cesium-137, known as products of nuclear fission.

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 also 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.

The water injections appear to have somewhat helped to prevent the crisis from worsening, but efforts to restore power and enhance cooling efficiency at the crisis-hit nuclear power plant is showing slow progress partly due to the radioactive pools of water found at the Nos. 1, 2, 3 and 4 units.

Workers there are planning to turn on the lights in the control room of the No. 4 reactor, while also trying to inject freshwater into tanks storing spent nuclear fuel 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.

Meanwhile, Tokyo Electric, known as TEPCO, is studying whether highly toxic plutonium is contained in the soil of the plant. The No. 3 reactor was using plutonium-uranium mixed oxide fuel for so-called ''pluthermal'' power generation.