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Thursday, July 21, 2011
Step 2 of nuclear crisis control
The government and Tokyo Electric Power Co. on Tuesday announced the start of Step 2 of the road map to bring the crisis in the stricken reactors of Tepco's Fukushima No. 1 nuclear power plant under control.
The most important goal in mitigating the crisis is to attain the cold shutdown of the reactors by mid-January 2012.
In Step 2, the government and Tepco hope to constantly keep the water temperature inside the reactors' pressure vessels at less than 100 C. At present, no means to gauge that temperature are available.
The government will start considering lifting evacuation orders for residents around the plant if the following two conditions are met: The temperature at the bottom of the pressure vessels must be less than 100 C and people's exposure to radiation caused by radioactive materials released from the plant must be greatly reduced.
The Nuclear and Industrial Safety Agency disclosed the goal of lowering the radiation level inside the plant's compounds from the current 1.7 millisieverts per year to 1 millisieverts per year.
But there are no guarantees that the goals will be achieved as expected. On June 27, Tepco started operating a circulatory water injection system to cool the reactors.
In this system, radioactively contaminated water leaking from the reactors is decontaminated and cooled, and then injected back into the pressure vessels in a circulating manner. The cold shutdown of the reactors depends on the reliability of this system.
But the system, comprising a loop of connected hoses extending some 4 km, has suffered a series of leaks and other problems. Its operation rate in the week that ended July 12 was only 73 percent. Tepco must newly install a system whose loop is shorter and has fewer chances of developing problems.
There are other worrisome factors. Radiation risks and hot weather may hamper the work of workers inside the plant. Heavy rain from a typhoon could cause a leak of radioactively contaminated water.
In Step 2, underground walls to prevent radioactive contamination of underground water are to be built in about three years. But this is too slow and shows the lack of a sense of crisis by the government and Tepco. They must build the walls quickly.
The government also must measure radiation levels precisely in areas around the plant and quickly disseminate relevant information to minimize threats to local residents' health.