Japanese nuclear reactor update: Amid signs of progress, new problems

Two Japanese nuclear reactors whose cooling systems were knocked out following an earthquake and tsunami were joined Monday morning by a third reactor that lost its cooling system. All three now are assumed at risk of partial or total meltdowns of their radioactive-fuel cores.

Still, one US nuclear expert said there was at least a glimmer of positive news emerging, with two of the three reactors showing signs of coming under control.

"Units No. 1 and No. 3 seem to be trending to more stable conditions and increasing safety margins," said Dave Lochbaum, a nuclear engineer and director of the Union of Concerned Scientist Nuclear Safety Program (UCS), a US nuclear safety watchdog group, in a conference call with reporters. No. 2, however, remains in an unstable, volatile situation, he said.

Two explosions over the weekend – apparently due to hydrogen buildup – ripped apart buildings housing the No. 1 and No. 3 reactors at the Fukushima I plant, about 150 miles north of Tokyo and owned by the Tokyo Electric Power Co. (TEPCO). The explosions injured workers and complicated efforts to flood the reactors to keep them cool.

Yet those explosions did not puncture the steel containment vessel – shaped like an inverted light bulb – now keeping high amounts of radioactivity bottled up, the plant owner said. Even so, all three reactors’ cores have been exposed to air, and so are assumed to have melted or become damaged to some degree, Japanese and international authorities reported.

Detection of the highly radioactive cesium-137 and iodine-131 outside the Fukushima I plant suggests that fuel has melted and at least some cores have sustained damage. On Monday morning in Japan, the No. 2 reactor joined the other two in losing coolant for a period, thus exposing to the air fuel rods that must be kept underwater in order to avoid partial or complete melting.

To get water into the reactor to cool it, authorities are now forced to vent radioactive steam. The plant is now emitting as much radiation in an hour as it would normally release in six months.

“The possibility that a large amount of radiation has been released is low,” Yukio Edano, the chief government spokesman, said at a news conference.

An emerging issue: spent fuel

Cooling the three reactors isn't the only problem. Cooling spent fuel stored in an adjacent spent-fuel pool at one troubled reactor could be an emerging issue, according to a TEPCO press release on March 13.

"We are currently coordinating with the relevant authorities and departments as to how to secure the cooling water to cool down the water in the spent nuclear fuel pool," the release said. Just how serious the cooling problem is remains publicly unknown, but raises concerns for some US nuclear experts.

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