A handout image supplied on 29 March 2012 by Tokyo Electric Power Company shows conditions at the Fukushima Daiichi nuclear plant. TEPCO

By HIROKO TABUCHI
29 March 2012

TOKYO – The damage to one of three stricken reactors at the Fukushima Daiichi plant could be worse than previously thought, a recent internal investigation has shown, raising new concerns over the plant’s stability and complicating the post-disaster cleanup.

The government has said that the plant’s three badly damaged reactors have been in a relatively stable state, called a cold shutdown, for months, and officials say that continues. But new tests suggest that the plant — which was ravaged last March when a powerful earthquake and tsunami hit the area — might not be as stable as the government or the operator of the plant, Tokyo Electric Power Company, or Tepco, had hoped.

The key to keeping the reactors stable is keeping their fuel rods cool with water.

The company announced this week that an examination of one reactor, No. 2, showed that the water level in an outer containment vessel was far lower than estimated, which could indicate that the already badly damaged uranium fuel might not be completely submerged and, therefore, is in danger of heating up.

Cooling water in that vessel, called the drywell, was just two feet deep, rather than the 33-foot level estimated by Tepco officials when the government declared the plant stable in December. That is probably not a problem for the fuel that the company says has leaked into the drywell from an inner containment vessel because Tepco says that melted fuel is unlikely to be higher than two feet.

But Tepco officials said the low water in the drywell left open the possibility that the water level in the leaking inner containment vessel, where most of the fuel is thought to be, was also low. Experts say that could leave the fuel there exposed and lead to more damage. The fuel would likely then leach more radioactive materials into the water that is flowing through the reactor to cool it.

That scenario would be particularly problematic since the company has long feared that some of the tons of water it is using to cool the reactors is escaping into the ground or into the ocean at the seaside plant. […]

Japan Nuclear Plant May Be Worse Off Than Thought

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