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| Blowing off ... fire erupts from the stricken nuclear plant at Fukushima, 250 kilometres north of Toyko. Photo: Digital Globe |
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Anatomy of a nuclear reactor. |
Glenda Kwek
The Sydney Morning Herald
An Australian scientist has dismissed fears of radiation risk from the spread of dangerous materials at the troubled Fukushima Daiichi nuclear power plant, saying the particles being released are short-lived ones that die within seconds.
Professor Barry Brook, the director of Climate Science at the University of Adelaide's Environment Institute, told ABC Radio's AM program this morning that "the worst is probably over" and that the temperature of the plants had dropped to 1 per cent of their original temperature.
The Japanese government yesterday urged people to observe a 20-kilometre exclusion zone around the plant, and told those living within a further 10-kilometre radius to stay indoors after a spike in radiation readings to 400 millisieverts an hour.
In France, the Nuclear Safety Authority said the Daiichi problems now equated to a six on the seven-point international scale for nuclear accidents, ranking the crisis second only in gravity to that of Chernobyl.
Its embassy in Tokyo also told French nationals yesterday afternoon to stay indoors and to close their windows, saying a low-level radioactive wind could reach the capital city within 10 hours, based on prevailing winds.
In the European Parliament in Brussels, Europe's Energy Commissioner Guenther Oettinger said the nuclear crisis was an "apocalypse" and that Tokyo had almost lost control of events at the plant.
"There is talk of an apocalypse and I think the word is particularly well chosen," he said.
'Worst is probably over'
But Professor Brook said: "To be honest, and I don't want to sound too optimistic, but I think the worst is probably over."
The environmental scientist said he did not think melting fuel rods could breach the 18-inch (45.7-centimetre) steel containment vessel.
The spike of radiation recorded in the nearby area after radioactive particles were released into the atmosphere from the plant were just spot readings, he added.
"These are what are called fission product gases. They are very short lived so that within seconds the vast majority of that radiation has decayed away.
"You see, what people are thinking of is a Chernobyl style accident, but in Chernobyl there was a special situation where the moderator in that reactor was not water, it was graphite - a form of carbon - and a fire started there and that burnt and burnt and burnt. It was very difficult to put out.
"And of course, that is the worst scenario possible because that carries all the deep fission products, and including the non-gaseous ones, up into the air as particles attached to the carbon.
"It can't happen here. These are light water reactors."
Professor Brook said dangerous particles from the materials could only spread within the nuclear plant's site as they were too heavy to carry over a large area.
"If someone can explain to me how those heavy particles, the heavy metals and even the non-gaseous fission products can be carried over a wide area, I'd like to hear it because I don't know a mechanism where that could happen in these sort of reactors," he said.
Public panic is the real risk
Dr Jim Smith of the School of Earth and Environmental Sciences at the University of Portsmouth, said the key issue was public panic, not radiation risk.
"It is important to focus on the radiation risk, but experience from past nuclear incidents has shown that the stress and panic caused by these events can be as bad as, or worse than, the direct threat from radiation," he said.
"Even after Chernobyl, although there were some severe health effects at the population level, the risk to individuals, except within the immediate vicinity of the plant, was very low. So - for people outside the immediate vicinity of the plant, even in meltdown on the scale of Chernobyl - the individual risk is likely to still be very low."
Professor Michael Reeks from the School of Mechanical and Systems at the University of Newcastle said a sense of perspective was needed and that the earthquake and tsunami were the real catastrophes.
“The Japanese earthquake and tsunami are natural catastrophes of historic proportions. The death toll is likely to be in the thousands.
"While the information is still not complete at this time, the tragic loss of life and destruction caused by the earthquake and tsunami will likely dwarf the damage caused by the problems associated with the impacted Japanese nuclear plants.”
Winds blowing material over Pacific Ocean
The UN weather agency has so far said that winds were dispersing radioactive material over the Pacific Ocean, away from Japan and other Asian countries.
Experts said the risk of radiation depends on the intensity of exposure, its duration and access to treatment.
"Radioactive material will reach Tokyo but it is not harmful to human bodies because it will be dissipated by the time it gets to Tokyo," Koji Yamazaki, professor of environment science at Hokkaido University, told Reuters.
"If the wind gets stronger, it means the material flies faster but it will be even more dispersed in the air."
Lam Ching-wan, a chemical pathologist at the University of Hong Kong, said "very acute radiation" was unlikely for the population.
But a longer-term exposure to radiation could raise the risk of thyroid and bone cancers and leukaemia for the general population, with children and foetuses especially vulnerable, he said.
Patrick Gourmelon, a leading researcher at the French Institute for Radioprotection and Nuclear Safety (IRSN), said that "even for relatively small doses, the risk of developing cancers rises".
"There are three weapons against contamination - evacuation, confinement and iodine," he told Agence France-Presse (AFP).
"The point is to prevent radioactive dust from entering the lungs and the digestive tract ... You take a good shower to remove any contact between the fallout and the skin, but you shouldn't scrub, because this helps particles to penetrate."
And that means no nail-biting, smoking and sucking or licking one's fingers either, he said.
Health risks from radiation (AFP)
Three things, say experts, determine whether a blast of radiation will be harmless, debilitating or lethal: the intensity of exposure, its duration and access to treatment.
Radioactive fallout includes caesium 137, a long-term element, and iodine, which is a short-term element. Intensity of exposure is measured in a unit called millisieverts (mSv), while the absorbed dose in the body is measured in milligrays.
Exposure
Small, controlled doses of exposure for medical applications cause no ill effects, doctors say. A brain scan, for example, generates 25 mSv, while a whole body scan puts out 150 mSv. A single dose of 1000 mSv, though, can cause temporary radiation sickness, including nausea and vomiting.
About half the people exposed to a 5000 mSv dose across the entire body would probably die, while 6000 mSv would be fatal without immediate treatment.
Exposure to 10,000 mSv in a single dose would lead to death "within a few weeks", said the World Nuclear Association, an industry group.
Japanese officials said radiation levels as of 10.20am (12.20pm AEST) on Tuesday were 30 mSv between the No.2 and No.3 reactors, and 400 mSv near No.3, and 100 mSv near No.4.
During a severe nuclear accident, exposure can reach several thousand mSv near the reactor core.
Radiation illness
The main health danger is cancer, especially leukaemia, along with lung, thyroid and colon cancer.
In cases of extreme irradiation, the body's bone marrow stops making red and white blood vessels, resulting in death. Cells inside the digestive tract are also especially vulnerable.
Over the long term, radiation can also damage DNA, leading to potential birth defects.
Treatment options
Potassium iodine pills taken beforehand can help prevent radioactive iodine in the air from settling in the thyroid and causing cancer, especially in infants and children.
The tablets are preferably taken an hour before a known fallout incident.
Japanese guidelines say the pills should be distributed when the likely absorbed dose of radioactivity is 100 milligray, a unit named after a British physicist.
Once exposed, the best first step is to throw away contaminated clothes and wash one's hair and body.
Some drugs help boost white-blood cell production inside bone marrow, and build up the body's compromised immunity.
with agencies
1 comment:
Wow! That is incredible!
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