April 20, 2011

Radiation levels in plants prevents work

Robots deployed inside two reactors at the Japanese nuclear plant overrun by last month's devastating tsunami have detected radiation levels too high for workers to enter, posing immediate challenges for a new plan to bring the ravaged complex under control by year's end.



On Sunday, two robots made their way into two of the reactor units, opening doors and navigating radioactive debris and puddles of water to return with temperature, pressure and radioactivity readings. The readings, released Monday, showed continued high radiation levels.
At Unit 1, robots detected up to 49 millisieverts per hour; at Unit 3, the reading was 57 millisieverts per hour. In recent weeks far higher readings have come from areas where contaminated water has accumulated, like the turbine building at Unit 2, where experts say the reactor pressure vessel may be cracked and leaking nuclear material.
Radiation limits for nuclear workers in the US are 50 millisieverts per year. Japan recently raised their radiation limits to 250 millisieverts per year. So current levels of radiation mean that workers are only able to work a few hours a year in the plant, raising questions about how workers will be able to bring the plant back to a cold shut-down. 
Japan outlined a timetable of between 6 to 9 months to gain control of the reactors and decontaminate the land surrounding the nuclear plant before residents will be allowed to return to their homes in the evacuation zone. 
But experts question the viability of the plan, which calls for swiftly building critical new cooling systems. Tokyo Electric faces "substantial barriers" in following the timetable, said Haruki Madarame, chairman of the Nuclear Safety Commission, an independent panel of experts appointed by the government to oversee the nuclear industry.


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