Tokyo Electric Power Co. and the government on Oct. 17 released a newly revised a road map to bring the stricken Fukushima No. 1 nuclear power plant under control. It shows that a “cold shutdown” of the Nos. 1, 2 and 3 reactors at the plant will be achieved by the end of the year. The reactor cores suffered meltdowns after the March 11 earthquake and tsunami inflicted severe damage, but the temperature in the lower part of the pressure vessels has now fallen below 100 C. As of Oct. 15, it was between 73 C. and 83 C.
The amount of radioactive substances released from the reactors has been halved from the level in September when the road map was earlier revised. It is estimated that the three reactors are now releasing radioactive substances at the rate of about 100 million becquerels per hour maximum, about one-eighth of a millionth the level immediately after the nuclear crisis started.
Tepco and the government said that with this rate, the annual exposure to radiation in the Fukushima No. 1 compound will be around 0.2 millisieverts maximum, lower than the goal of one millisievert. They also said that the level of contaminated water in the reactor building basements has stabilized. In view of those factors, Tepco and the government said in their newly revised road map that the “cold shutdown” will be achieved by the end of this year.
But it must be emphasized that the state of “cold shutdown” that Tepco and the government speak of does not meet the true definition of a cold shutdown — when the temperature inside the pressure vessel is below 100 C and the reactors no longer release radioactive substances. Therefore, achieving this state would not mean that the nuclear crisis has been brought under control.
It is believed that the meltdown caused molten nuclear fuel to fall through the bottom of the pressure vessels and enter the containment vessels. Thus measuring only the temperature at the lower part of the pressure vessels does not reveal the true conditions inside the reactors.
In addition, a large amount of spent nuclear fuel remains stored inside pools in the reactor buildings. The amount of contaminated water has not decreased. An underground wall to prevent contamination of underground water has not yet been constructed. In short, no optimism can be warranted about ending the nuclear crisis anytime soon.
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