• Kyodo News


Since the crisis at the Fukushima No. 1 nuclear plant began, 17 workers have suffered radiation of more than 100 millisieverts, the maximum annual exposure for nuclear plant workers until the level was raised amid the emergency.

The employees were engaged in critical work to lift the stricken six-reactor plant out of disaster amid high risks of exposure to radiation.

Tokyo Electric Power Co., the plant operator and the nation’s biggest utility, says it is “up to each individual to decide whether to continue” working at the plant.

But an expert familiar with working conditions said that in the case of subcontractors, “The reality is that they are not in a position to decline job offers that they may not like, because they know that would affect orders in the future.”

At the Fukushima plant, efforts to restore power and other equipment are being carried out by workers facing huge radiation exposure risks.

On Thursday, three workers laying cables at Fukushima’s No. 3 reactor were exposed to high levels by standing in water apparently containing radioactive materials.

Nuclear plant workers are typically allowed radiation exposure of up to 50 millisieverts per year, and 100 in an emergency, but the Health, Labor and Welfare Ministry raised the limit for workers handling the crisis at Fukushima to 250 millisieverts.

If a human absorbs 500 millisieverts, experts say the impact will start manifesting itself in such forms as a reduction in the lymphocyte count. Tepco says if a worker’s exposure exceeds 100 millisieverts, he will be asked if he still wants to continue working so long as his exposure does not top 250 millisieverts.

The utility said it has never checked to see if anyone has ever declined to work.

Experts differ over the advisability of these yardsticks on radiation for workers.

Kiyoshi Sakurai, a commentator on technology issues, said: “250 millisieverts is a reasonable figure. Given residents are getting anxious and the current state of affairs, workers should not be allowed to decline assignments.”

Keiji Miyazaki, professor emeritus in nuclear engineering at Osaka University, said: “It is an emergency situation. To put an end to it soon, those who are knowledgeable are called on to stay and conduct work.”

In contrast, Mitsuhiko Tanaka, a former engineer in nuclear plant designs, said, “I would think it is a terrible job, but if you are an employee of a subcontractor, you will probably be unable to decline, thinking about future (work for their employer).”

At Fukushima No. 1, workers continue to fight against clock. The limited exposure of 100 millisieverts per worker could impede and limit what they can do.

Tepco says gradual radiation exposure is threatening even those who are working in a building fortified against quakes and radiation that accommodates the crisis team within the plant complex.

Nuclear plant workers risk exposure to various forms of radiation.

Gamma rays, like X-rays, penetrate the human body. Radioactive iodine, one of the materials released in the Fukushima crisis, emits gamma rays, a factor that could hinder restoration work. Tepco said two of the three workers exposed to high levels of radiation are suspected of having suffered gamma radiation.

Gamma radiation is caused when uranium undergoes nuclear fission, which also produces neutron radiation, capable of deeply penetrating the body.

Alpha radiation of helium nuclei is harmful but loses kinetic energy easily, limiting its sphere to a few centimeters in the air. It also can’t penetrate water or skin and a sheet of paper can easily shield against it.

Beta particles are electrons that penetrate the human body by around 8 cm.

Plant workers wear Tyvek protective suits that prevent radioactive materials touching the skin or infiltrating the body, but they are not designed to shield against most types of radiation.

Each day, several hundred workers enter nuclear plants, wearing in total 500 to 1,000 suits that are discarded after use, according to Tepco.

“The working environment where ‘irradiated workers’ engage in assignments in radiation-filled sites has been singled out as a problem,” said former nuclear plant engineer Tanaka.

The crisis at Fukushima once again exposed the dark side of nuclear plants, a major source of the nation’s electricity supply.

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