Japan's radiation leak: Shades of Three Mile Island and Chernobyl?

Japan’s unfolding nuclear power crisis remains at an unstable, volatile stage, warn US nuclear experts who, while hopeful, say past nuclear accidents – at Three Mile Island and Chernobyl – grew far worse over several days before being controlled.

Their comments, which came during a Saturday conference call convened by anti-nuclear power groups, were in sharp contrast with reports by the Japanese government which appeared to indicate the main crisis in one of its nuclear reactors was past, although a state of emergency remained in effect for five reactors.

Japanese soldiers were reported pumping seawater into the No. 1 reactor at the Fukushima I power plant 150 miles north of Tokyo, to keep it cool. But one US expert characterized the move as an apparent last-ditch “Hail Mary” effort that could easily fail and be followed by a major radioactive release.

An enormous explosion Saturday morning – possibly due to a buildup of hydrogen gas – destroyed most of a secondary containment building housing the No. 1 reactor, but was reported by a government spokesman not to have breached a critical inner steel liner – the reactor’s primary containment vessel.

On Saturday, the Japanese government reported five reactors at two different nuclear power plants – Fukushima I and Fukushima II – to be in a state of emergency following the massive earthquake that hit Japan Friday. A total of 11 of the nation’s 54 reactors shut down following the quake, knocking out about 30 percent of the nation’s power. Still, Japanese officials were matter-of-fact.

Chief Cabinet Secretary Yukio Edano told reporters Saturday that radiation around the plant had started to decrease. A “tiny” amount of radiation had leaked earlier in the day when officials attempted to relieve pressure inside the reactor.

“We have confirmed that the walls of this building were what exploded, and not the reactor’s container,” Mr. Edano said, adding, “There was no large amount of radiation leakage outside. At this point, there has been no major change to the level of radiation leakage outside, so we'd like everyone to respond calmly.”

Evacuations expanded around reactors

Over the past 24 hours, however, government officials have expanded evacuations around the reactors, and conditions seemed to seesaw wildly at the Fukushima I complex, where the No. 1 and No. 2 reactors lost their backup cooling systems powered by diesel generators within an hour after the quake.

A pressure build-up was soon reported in reactor No. 1, and coolant loss and spiking temperatures were reported in No. 2. Despite venting of gases at the reactors, the explosion Saturday morning destroyed the containment building of the No. 1 reactor.

Tokyo Electric Power Co., which operates the plants, reported that an equipment failure had made it "impossible to cool two reactors" at the Fukushima I plant. Air from inside the plant that might contain radioactive materials would be vented from the plant, the company told NHK World late Friday.

Following the Saturday explosion, radiation levels that were reported higher than normal around the site were said by government spokesmen to have declined. Yet the government soon widened an earlier evacuation notice from a 3-kilometer (1.8-mile) radius of the Fukushima I nuclear power plant to 20 kilometers (12.4 miles). An evacuation zone around the Fukushima II plant was set at 10 kilometers. Little is known about conditions at the Fukushima II facility.

Video of the aftermath of the explosion appeared to show that the No. 1 reactor’s containment building had been destroyed. But the inner containment shell appeared not to have been breached by the explosion, analysts said.

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