Achieving a "cold shutdown" of a nuclear reactor is not difficult as long as the reactor is not broken. A cold shutdown is defined by experts as a situation in which nuclear reactors whose operations are suspended are being stably cooled down and the temperatures in them are kept below 100 degrees Celsius.
However, it is no easy task to achieve a cold shutdown at the tsunami-hit Fukushima No. 1 Nuclear Power Plant where fuel has melted and holes have developed in damaged reactors.
Goshi Hosono, state minister for the prevention of nuclear accidents, told the International Atomic Energy Agency (IAEA) annual general meeting under way in Vienna that Tokyo will do its best to achieve a cold shutdown of the stricken reactors at the plant by the end of this year. His remark suggests that the government intends to bring forward its target of achieving a stable cool-down of the troubled reactors and of substantially reducing the amount of radioactive substances released from the plant by January 2012.
The temperature at the bottom of the No. 1 reactor's pressure vessel has been stabilized at less than 100 degrees Celsius, and that of the No. 3 reactor has recently been kept below that level. Hosono appears to have made the remark at the IAEA conference while keeping in mind these positive signs.
It is a matter of course for the government to try its utmost to bring the crippled reactors under control as soon as possible, and it is important for it to show its determination to achieve this goal to the international community.
At the same time, however, it is notable that the government has failed to clarify what a cold shutdown at the Fukushima plant specifically means. Currently, water contaminated with radioactive materials is purified and reused to cool down reactor cores as a last-ditch measure, and plant operator Tokyo Electric Power Co. (TEPCO) is unlikely to be able to use a conventional cooling system in the foreseeable future.
If the cooling system with a total extension of four kilometers develops trouble, the temperatures of the reactor cores could rise again. Since it remains unclear where the melted fuel is situated in the troubled reactors, the temperatures of the pressure vessels alone are far from convincing.
Under these circumstances, the phrase, "cold shutdown," should not be used in a casual manner without clearly defining it. It is important to grasp the actual conditions of the reactors and fuel as accurately as possible and take appropriate countermeasures in a well-organized manner.
The lifting and reviewing of evacuation advisories depends largely on whether the cold shutdown of the stricken nuclear reactors can be achieved. Therefore, the government should specifically explain the conditions of the reactors and risks involving them to the public.
In anticipation that the reactors will be stabilized in a relatively short period, the government is set to lift its designation of areas 20-30 kilometers from the nuclear power station as "emergency evacuation preparation zones" as early as this month. In these areas, residents are allowed to stay in their neighborhoods, but kindergartens and schools remain closed. Such a contradiction should be eliminated according to the circumstances of each of these areas.
On the other hand, it is indispensable to regularly measure the precise levels of radiation and decontaminate areas tainted with radioactive substances so that residents can return to their neighborhoods without worries about being exposed to radiation. Moreover, it is necessary to speed up efforts to repair and build public infrastructure in the affected areas.
Hosono has sought cooperation from the IAEA to share its expertise in decontamination. It is an important task to bring together the knowledge of the international community to revive crisis-hit Fukushima.
(Mainichi Japan) September 21, 2011