Unknown Where Melted Fukushima Nuclear Cores Are Now

Tatsuo Nakajima / Yomiuri Shimbun Staff Writer

The latest timetable for bringing a nuclear fuel meltdown at the Fukushima No. 1 nuclear power plant under control shows the situation is no longer in the critical condition it was immediately following the accident, but many issues remain unsolved.

The government and Tokyo Electric Power Co. have revised the timetable for the seventh time in the eight months since the crisis began. Data suggests the reactors and radioactive material are under control, and the power plant will achieve a cold shutdown once required conditions are confirmed.

However, the status of the molten nuclear fuel is unclear. It is not known how the fuel, believed to have partially melted through pressure vessels of the reactors and into containment vessels, has dispersed and how much lies in water.

It is questionable to assess the situation as nearly a cold shutdown. Usually, to achieve a cold shutdown, all fuel rods should be cooled under water, and nuclear fuel, pressure and containment vessels should be intact and in good condition.

The situation at the nuclear plant does not meet this definition. Is it appropriate for the government and TEPCO to call the current status nearly a cold shutdown?

On Nov. 2, TEPCO said a small-scale recriticality incident--in which nuclear fuel achieves a fission chain reaction--may have taken place at the No. 2 reactor of the power plant, creating a small panic. The company later said xenon discovered at the plant was the result of spontaneous fission, not a nuclear chain reaction known as recriticality as had been feared.

TEPCO should have been able to coolly handle the detection of xenon, but it failed to do so as it had not properly prepared necessary data. These matters should not be dealt with in a hurried and sloppy manner as the end of the year, the target for achieving cold shutdown, approaches.

There are many other unsolved issues, including how to cope with contaminated water said to be accumulating at a rate of 200 to 500 tons a day in underground areas of the reactor buildings. The government and TEPCO must thoroughly solve these issues without being bound by their timetable.

(Nov. 19, 2011)

SOURCE: http://www.yomiuri.co.jp/dy/national/T111118006066.htm