Fukushima workers suffer contamination; fears loom of crack in reactor vessel

By Dorothy Davis

The International Atomic Energy Agency (IAEA) has confirmed reports that three workers at the Fukushima Daiichi nuclear power complex have been hospitalized after they were exposed to higher than normal radiation levels Thursday.

The IAEA report outlines that the three contract workers were laying cables in the turbine building of the Unit 3 reactor where they received a radiation dose in the range of 170-180 millisieverts. The average dose for a nuclear plant worker is 50 millisieverts; however, the daily limit for emergency workers at the site has been set to 250 millisieverts.

For comprehensive coverage of the Japanese nuclear power disaster and efforts under way to resolve it, visit PennEnergy’s Japan Earthquake and Nuclear Emergency 2011 special section. 

It is thought the workers ignored their dosimeters' alarm believing the warnings to be false based on survey results of radiation in the area from the day before. They continued working with their feet in contaminated water for as much a three hours as they labored to cool the damaged reactor.

Once higher levels of contamination were recognized the workers were removed from the reactor site and washed in an attempt to remove radioactivity, then taken to the Fukushima University Hospital for an initial examination. Next they were transferred to Japan's National Institute of Radiological Sciences where they are expected to remain for monitoring over the next four days.

The incident has sparked concerns that the Unit 3 reactor vessel may be compromised, which would result in a significant release of radiation. Following the incident, Hidehiko Nishiyama, deputy director-general of the Japan Nuclear and Industrial Safety Agency expressed that the accident may indicate the contaminated water pools at the Unit 3 building may be the result damage to the rector.

“The contaminated water had 10,000 times the amount of radiation as would be found in water circulating from a normally operating reactor," said Nishiyama. "It is possible that there is damage to the reactor."

The possibility of a breach to the containment structures at the core of the Unit 3 reactor is particularly troubling because it is the only Unit at the Fukushima complex to utilize a MOX fuel mix which is significantly more toxic than the uranium used in the other five reactors.

MOX is a mixed oxide nuclear fuel that contains more than one oxide of fissile material. MOX is more dangerous than standard uranium fuel because it contains plutonium, which heats up more than uranium and can cause hot spots during a loss of coolant incident. Plutonium also makes control rods and boron less effective in slowing down a nuclear reaction - two crucial elements in the emergency shutdown of a reactor during a critical incident. It also releases more harmful radiation than pure uranium fuel in the case of a meltdown. For these reasons, nuclear safety campaigners in Japan succeeded in limiting the amount of plutonium in Japan's MOX to 6 percent (In France, by comparison, plutonium makes up 30 percent of MOX fuel).

There has been no official confirmation that any of the protective shielding for the six reactors at the Fukushima complex has been damaged, but the Japanese has called for a thorough investigation into why such elevated levels of radiation had suddenly come to light.

The IAEA has dispatched additional teams to Japan to assist in the response to the Fukushima nuclear emergency. These IAEA specialists will continue to supplement Japan's radiation monitoring efforts. Team members include worker radiation protection experts and safeguards department officials.

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