Japan nuclear crisis reaches new levels

Japan's nuclear crisis may have taken its most dangerous turn yet after a US official said one of the pools containing highly radioactive spent fuel rods at the stricken plant had run dry.

One nuclear expert said that there was now even a possibility that the disaster may approach the extent of the Chernobyl accident, the worst ever in the industry's history. When the Chernobyl plant in Ukraine exploded in 1986 it spewed a radiation cloud over a large area of Europe.

And a nuclear engineer said that it may be time to consider ways to bury or cover the entire complex in some kind of material that would stop radiation from leaking into the atmosphere.

Triggering the new levels of alarm were comments by U.S. Nuclear Regulatory Commission Chairman Gregory Jaczko in Congress. "There is no water in the spent fuel pool and we believe that radiation levels are extremely high, which could possibly impact the ability to take corrective measures," he said.

Japanese officials have been working desperately for two days to try to get more water into the pool to cover the rods, which remain hot for months after they are removed from the reactors and can quickly release radioactive components if exposed to the air.

"If they don't get water to these spent fuel pools in view of the containment breaches in the other plants the actual radiation releases could approach that category of Chernobyl," said Victor Gilinsky, who was an NRC commissioner at the time of the Three Mile Island accident in 1979, which was the worst nuclear accident in US history.

Earlier Japanese authorities told the International Atomic Energy Agency that radioactivity was being released directly into the air at the pool for the No.4 reactor at the Fukushima Daiichi plant. Experts say the pools could present a bigger threat to public health than the reactors, which appear to be still encased in steel containment systems.

"Up until now they have not been able to get close to the spent rods, as even with protective clothing it only stops workers from breathing in radioactive particles, not from radiation itself," Dr Peter Hosemann PHD of the University of California Berkeley Nuclear Engineering Department said Tuesday.

While the building holding the rods has been rocked by fire and a blast, officials in Japan had not said how much water remained in the 40-foot deep tanks.

James Acton, Associate in the Nuclear Policy Program at the Carnegie Endowment for International Peace, said in an interview before Jaczko's comments that it appeared there was a leak in the pool.

"There is either a leak in the spent fuel pool or the rods are hot enough to cause evaporation," Acton said.

When a fuel rod is exposed to the air the zirconium metal cladding on the rods can easily catch on fire, releasing a deadly mix of radiation into the atmosphere. The earlier fires and explosion in the area of the spent fuel storage tank left the pool partly open to the air allowing the radiation to escape into the atmosphere.

Experts say the water should remain at least eight feet over the spent fuel to maintain acceptable radiation levels but the level usually is kept much higher.

"As the water drains there's going to be less stability - and higher levels of radiation released," said Tara Neider, President and CEO of Areva Federal Services, a US arm of the world's biggest nuclear power plant builder, French giant Areva SA.

Tokyo Electric Power Co (TEPCO), the operator of the six-reactor complex, was considering spraying water into the spent fuel pools through the holes in the roof by helicopter but later canceled that mission.

Arnie Gundersen, a 29-year veteran of the nuclear industry who has worked on reactors similar to the Daiichi plant and is now chief engineer at Fairewinds Associates Inc, warned that dropping water on the spent fuel pool could make matters worse.

"It's a bad idea to drop water onto the fuel racks. You could get an inadvertent criticality. That means you could have a nuclear reaction, similar to that in a reactor core, in the fuel pool," Gundersen said.