JAPANESE NUKE CRISIS TAKES DANGEROUS TURN
Danny Rose, AAP Medical Writer, AAP
March 17, 2011, 7:05 pm
Efforts to make Japan's quake and tsunami-hit nuclear plants safe and halt their radioactive fallout have taken a "very dangerous" turn, Australian experts say.
They say the threat to human health is still confined within the exclusion zone around the stricken plants, in the absence of a major explosion that could send large amounts of radioactive material into the atmosphere.
However, work to cool the cores of the damaged plants has taken a backwards step with problems emerging at a fourth plant.
"The critical thing in this situation at the moment is that (Fukushima Daiichi nuclear plants) unit 1, 2 and 3 are under sea water injection," said Dr John Price, a former member of the Safety Policy Unit of the UK's National Nuclear Corporation and former Professor at Monash University, now private consultant.
"That means they are now pumping sea water into those three units, if that keeps up those units are stable.
"And we go to unit 4 and the statement is much more obscure, the water injection was stopped."
Last line of defence
Military helicopters have dumped water to cool fuel rods as the US expresses growing alarm about leaking radiation.
It is understood the problem at unit 4 is based not on cooling the shut-down reactor itself but that a nearby storage pool, which holds spent but still highly radioactive fuel rods, was breached and so water kept draining out and exposing parts of the rods to the air.
"That's a very dangerous situation because the storage pond is in the building but not within the containment vessel for the reactor, so any radiation released from there can go directly into the atmosphere," said Mr Peter Burns, former chief executive of the Australian Radiation Protection and Nuclear Safety Agency.
"It will make it very difficult for operators to go in there and work because the radiation will get to very high levels and that's why they are trying extreme measures ... water bombing with helicopters."
The exposed fuel rods pose a much greater radiation risk to emergency crews working inside, and nearby, the unit 4 section, Mr Burns said, but he added the risk to the Japanese populace outside the exclusion zone still remained "extremely small".
It was the venting of radioactive steam that was the major risk at the site, he said, and the plants had been spared a major explosion involving the more hazardous fission material inside the reactors or in spent fuel rods.
"The health risk to all people in the quake zone, and particularly if you consider beyond the 20km evacuation zone and beyond the 30km exclusion zone where people are being told to shelter, the risk is extremely small at the moment," Mr Burns said.
"There have been no reports of actual large releases (of radiation) that has gone back inland."
Professor Stephen Lincoln, an environmental chemist at the University of Adelaide, said the steam probably contained nitrogen 16, which is radioactive with a half-life of 10 minutes.
"This means that after 10 minutes the radioactivity is down to a half, after 20 minutes a quarter, after 30 minutes one eighth ... and so on (leading to) no long-term environmental consequences," Prof Lincoln said.
The fuel rods contain uranium 235 and possibly plutonium 239 and they could decay completely when exposed to air, allowing the "escape of dangerous radioactive fission products such as iodine 131 (half-life 8 days), cesium 137 (half-life 30 years) and strontium 90 (half-life 29 years)".
The iodine accumulates in the thyroid where it can cause cancer, but this risk can be addressed by taking tablets.
Cesium accumulates in the body's soft tissues while strontium accumulates in the teeth and bones, where it can cause cancer.
These cannot be easily removed from the body once exposed.
International reaction
While Japanese officials scrambled with a patchwork of fixes, the top U.S. nuclear regulator warned that the cooling pool for spent fuel rods at reactor No.4 may have run dry and another was leaking.
Gregory Jaczko, head of the Nuclear Regulatory Commission, told a parliamentary hearing that radiation levels around the cooling pool were extremely high, posing deadly risks for workers still toiling in the wreckage of the earthquake-shattered power plant.
"It would be very difficult for emergency workers to get near the reactors. The doses they could experience would potentially be lethal doses in a very short period of time," he said in Washington.
The plant operator said it believed the No.4 reactor spent-fuel pool still had water as of Wednesday, and made clear its priority was the spent-fuel pool at the No.3 reactor. On Thursday morning alone, military helicopters dumped around 30 tonnes of water, all aimed at this reactor.
Inside the complex, torn apart by four explosions since a 9.0-magnitude earthquake and tsunami hit last Friday, workers in protective suits and using makeshift lighting tried to monitor what was going on inside the six reactors. They have been working in short shifts to minimise radiation exposure.
U.S. officials took pains not to criticise the Japanese government, which has shown signs of being overwhelmed by the crisis, but Washington's actions indicated a divide with its close ally about the perilousness of the situation.
Neighbouring China wanted Japan to report developments "accurately" and quickly, a government spokeswoman said.
"The worst-case scenario doesn't bear mentioning and the best-case scenario keeps getting worse," Perpetual Investments said in a note on the crisis.
Japan said the United States would fly a high-altitude drone over the stricken complex to gauge the situation, and had offered to send nuclear experts.
A State Department official said flights would be laid on for Americans to leave and family of embassy staff had been authorised to leave if they wanted.
Health experts said panic over radiation leaks from the Daiichi plant, around 240 km (150 miles) north of Tokyo, was diverting attention from other life-threatening risks facing survivors of last Friday's earthquake and tsunami, such as cold, heavy snow in parts and access to fresh water.
The latest images from the nuclear plant showed severe damage to some of the buildings after the four explosions. Two of the buildings were a mangled mix of steel and concrete.
Sebastian Pflugbeil, president of the private German-based Society for Radiation Protection, said Japan's efforts to pull the Fukushima plant back from the brink signalled "the beginning of the catastrophic phase."
"Maybe we have to pray," he said, adding that a wind blowing any nuclear fallout east into the Pacific would limit any damage for Japan's 127 million people in case of a meltdown or other releases, for instance from spent fuel storage pools.
Morgues searched in the hunt for Australian bodies
Australian officials are searching morgues, hospitals and emergency shelters for 55 Australians still missing in devastated Japan.
Foreign Minister Kevin Rudd told the ABC it was encouraging that the number of Australians missing had dropped significantly.
But he added: "I'm just worried, and I'll be worried until we account for every last one of them."
He said there was some good news on Wednesday, when a consular team deep inside the disaster zone located a group of Australians.
"... we came across and found a group of I think either six, eight or 10 Australians and that just helps bring the number down," Mr Rudd said.
"Our teams on the ground are going through morgues, they're going through hospitals, they're going through emergency shelter facilities and just doing it literally by hand, because there's no other way to do it."
He repeated the government's advice that Australians whose presence in Japan was not essential should leave the country if they could.
Looking back at Chernobyl.
One of the reasons for that was the extreme pressure infrastructure was under in the quake- and tsunami-ravaged country, potential health risks and ongoing aftershocks.
Mr Rudd also said the government was continuing to take advice on the nuclear threat posed by the severely damaged Fukushima nuclear plant from Australia's nuclear authority.
He said the US nuclear regulator had revised its position overnight and said the exclusion zone around the plant should be extended from 20-to-30km to more like 50-or-60km.
"We are now examining that ... and will make any appropriate adjustments to the travel advisory for Australians as well," he said.
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