Japan Reactor Damage Worse

Monday, May 16, 2011 @ 02:05 PM gHale

One of the reactor cores at the Fukushima Dai-Ichi nuclear plant suffered more serious damage than previously thought, officials said.

The water level is 1 meter (3.3 feet) below the base of the fuel assembly which means fully exposed fuel rods in the core of the No. 1 reactor, said Junichi Matsumoto, a general manager at Tokyo Electric Power Co. (Tepco) in a published report. Melted fuel has dropped to the bottom of the pressure vessel and they are still trying to cool it, Matsumoto said.

Japan is trying to contain the worst nuclear disaster since Chernobyl after a quake and tsunami two months ago knocked out power and cooling systems at the Fukushima station. While authorities have previously suspected a partial meltdown at unit 1, high radiation levels had prevented workers from entering the building to check the damage until last week.

On the good side, there is no danger of another explosion like the one that blew the roof off the reactor in March, Matsumoto said at the briefing.

As a part of the system, fuel rods submerge in water to prevent overheating that would crack the casing and release radiation. But there are holes in the base of the pressure vessel, and most of the fuel has likely melted, Kyodo News reported, citing the utility. It’s possible the fuel leaked into the containment vessel after the explosion, according to the report.

Flooding the chamber was one of the steps Tepco outlined in April to bring the crisis under control.

“The plan needs to be revised,” Matsumoto said. “We can’t deny the possibility that a hole in the pressure vessel caused water to leak.”

The company doesn’t know how long the rods have suffered exposure, it said in the briefing.

The six-reactor complex, Japan’s third-largest by capacity, has been emitting radiation since March 11 and the severity rating of the accident is now as high as Chernobyl. The station is 220 kilometers (137 miles) north of Tokyo.

The U.S. Nuclear Regulatory Commission (NRC), which has officials in Japan monitoring the crisis, hasn’t changed its advice of March 16, urging U.S. citizens to stay 50 miles from the stricken plant, said Eliot Brenner, an NRC spokesman.

Tepco has said it expects a sustained drop in radiation levels at the entire plant by July, according to its April 17 plan. Following that, a cold shutdown of reactors No. 1, 2 and 3 may take place as early as October, the utility said at the time.

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