2 partial meltdowns,a 2nd explosion and cooling problems at 4 reactors in Japan

By Hiroko Tabuchi and Matthew L. Wald, New York Times, March 13, 2011
TOKYO — Japanese officials struggled on Sunday to contain a widening nuclear crisis in the aftermath of a devastating earthquake and tsunami, saying they presumed that partial meltdowns had occurred at two crippled reactors and that they were bracing for a second explosion, even as they faced serious cooling problems at four more reactors.
An explosion occurred at the Daiichi nuclear power plant in northern Japan after the earthquake.
The emergency appeared to be the worst involving a nuclear plant since the Chernobyl disaster 25 years ago. The developments at two separate nuclear plants prompted the evacuation of more than 200,000 people. Japanese officials said they had also ordered up the largest mobilization of their Self-Defense Forces since World War II to assist in the relief effort.
On Saturday, Japanese officials took the extraordinary step of flooding the crippled No. 1 reactor at Fukushima Daiichi Nuclear Power Station, 170 miles north of Tokyo, with seawater in a last-ditch effort to avoid a nuclear meltdown. That came after an explosion caused by hydrogen that tore the outer wall and roof off the building housing the reactor, although the steel containment of the reactor remained in place.
Then on Sunday, cooling failed at a second reactor — No. 3 — and core melting was presumed at both, said the top government spokesman, Chief Cabinet Secretary Yukio Edano. An explosion could also rock the No. 3 reactor, Mr. Edano warned, because of a buildup of hydrogen within the reactor.
“The possibility that hydrogen is building up in the upper parts of the reactor building cannot be denied. There is a possibility of a hydrogen explosion,” Mr. Edano said. He stressed that as in the No. 1 unit, the reactor’s steel containment would withstand the explosion.
“It is designed to withstand shocks,” he said.
Officials also said they would release steam and inject water into a third reactor at the Fukushima Daiichi plant after temperatures rose and water levels fell around the fuel rods.
Cooling had failed at three reactors at a nuclear complex nearby, Fukushima Daini, although he said conditions there were considered less dire for now.This too By Peter Small, Toronto Star, March 12, 2011
An accident at Fukushima Daiichi nuclear power plant on Japan’s earthquake-ravaged east coast could become one of the worst in history, second only to Chernobyl, a Canadian expert says.
But John Luxat, NSERC industrial research chair in nuclear safety analysis at McMaster University, (Hamilton, Ontario) said the plant is unlikely to release anywhere near the massive doses of radiation as in that 1986 Ukrainian disaster.
A worst-case scenario would be more like the partial meltdown in 1979 at the Three Mile Island plant in Pennsylvania, he said.
There, a cooling system malfunction led to the release of significant radiation, forcing 140,000 to evacuate their homes.
In Chernobyl – the worst nuclear plant disaster in history –a power output surge led to a reactor vessel rupture, sending a plume of radioactive fallout into the atmosphere and over an extensive area.
What happens next at the 40-year-old Japanese power plant depends on whether workers can get enough water back into the reactor vessel to cool it down, Luxat said Saturday.
“At this stage it’s difficult to predict how serious it could develop.”
The accident occurred as pressure in one of six reactors started to rise as Japan’s 8.9-magnitude earthquake knocked out backup and primary power to the cooling system.
An explosion occurred as plant operator Tokyo Electric Power Co. tried to reduce pressure in the core.
“The big reactor vessel is like a big pot full of water,” Luxat said. If it can’t be cooled, it boils like a kettle, turning water into steam.
As the water boils away, nuclear fuel is exposed, causing it to overheat. That produces hydrogen gas, which accentuates the heating process and leads to a release of radioactivity, he said.
“The worst-case scenario is that they actually get a large amount of molten material fuel within the vessel and it could potentially melt down out of the vessel onto the floor,” Luxat said. Other sources indicate the Japanese people are afraid, not only of a nuclear meltdown, but that the officials responsible are not providing a full account of the danger. In their attempt to minimize panic, perhaps, according to several reports, both in print and on television, officials may be withholding information that may be more serious than what has been released so far.
Japan has some 50-plus nuclear reactors (reports vary from 53-55) and with both the initial shocks from the earthquake, the largest since data has been collected in 140 years, and aftershocks, there could be more danger to more reactors than the first one at Fukushima Daiichi.
Already reports indicate that excessive signs of radiation have been found on some Japanese people, with thousands being evacuated in a circle at least of at least 20 miles' radius.
The world watches and waits while all efforts are dedicated to preventing a significant radioactive meltdown.
We can only hope those efforts are successful given the potential spread of the fallout dust.