Subject: Fukushima : What Went Wrong
Has there been a leakage of radioactive material?
Yes. Local government officials in Fukushima say 190 people have been exposed to
some radiation. An American warship, the USS Ronald Reagan, has detected low
levels of radiation at a distance of 100 miles (161km) from the Fukushima plant.
How much radioactive material has escaped?
The Japanese authorities say only low levels of radiation have been detected
outside the plant. The International Atomic Energy Agency has described it as a
level four event on the International Nuclear and Radiological Event Scale
(INES), which is used for an accident "with local consequences". No abnormal
levels of radiation have been detected in Russia.
What type of radioactive material has escaped?
There are reports of radioactive isotopes of caesium and iodine in the vicinity
of the plant. Experts say it would be natural for radioactive isotopes of
nitrogen and argon to have escaped as well. There is no evidence that any
uranium or plutonium has escaped.
What harm do these radioactive materials cause?
Radioactive iodine could be harmful to young people living near the plant. After
the 1986 Chernobyl nuclear disaster there were some cases of thyroid cancer as a
result. However, people who were promptly issued with iodine tablets ought to be
safe. Radioactive caesium accumulates in soft tissue, while plutonium
accumulates in the bone and liver. Radioactive nitrogen decays within seconds of
its release, and argon poses no threat to health.
How did the radioactive materials escape?
There have been problems with cooling systems, causing the reactors to overheat.
Production of steam has caused pressure to build up inside the reactor, so small
amounts of steam have been deliberately released. On Tuesday another reactor
exploded, possibly causing a crack in its suppression chamber. This would allow
steam to escape continuously, but the situation is unclear. Experts say that the
presence in the steam of caesium and iodine - which are among the by-products of
nuclear fission - suggests that the metal casing of some of the fuel rods has
melted or broken. But the uranium fuel itself has a very high melting point so
it is less likely to have melted, let alone vapourised.
Could radioactive materials have escaped by any other means?
The authorities have pumped sea water into three reactors. This water will be
contaminated by its passage through the reactor, but it is currently unclear
whether any of it has been released into the environment.
How long will any contamination last?
Radioactive iodine decays quite quickly. Most will have disappeared within a
month. Radioactive caesium does not last long in the body - most has gone within
a year. However, it lingers in the environment and can continue to present a
problem for many years.
Has there been a meltdown?
The term "meltdown" is used in a variety of ways. As noted above, the reported
detection of radioactive caesium and iodine may indicate that some of the metal
casing enclosing the reactors' uranium fuel has melted (a "fuel-rod meltdown").
However, there is as yet no indication that the uranium fuel itself has melted.
Still less is there any indication of a "China Syndrome" where the fuel melts,
gathers below the reactor and resumes a chain reaction, that enables it to melt
everything in its way, and bore a path deep into the earth. If there were to be
a serious meltdown, the Japanese reactor is supposed to be able to handle it,
preventing the China Syndrome from taking place. Reports suggest that underneath
the reactor, within the outer containment vessel, there is a concrete basin
designed to capture and disperse any molten fuel.
Could there be a Chernobyl-like disaster?
Experts say this is highly unlikely. The chain reaction at all Fukushima
reactors has ceased. The explosions that have occurred have taken place outside
the steel and concrete containment vessels enclosing the reactors. At Chernobyl
an explosion exposed the core of the reactor to the air, and a fire raged for
days sending its contents in a plume up into the atmosphere. At Fukushima the
explosions - caused by hydrogen and oxygen vented from the reactor - have
damaged only the roof and walls erected around the containment vessels.
Could there be a nuclear explosion?
No. A nuclear bomb and a nuclear reactor are different things.
What caused the hydrogen release from the reactor?
At high temperatures, steam can separate into hydrogen and oxygen in the
presence of zirconium, the metal used for encasing the reactor fuel. This
mixture is highly explosive.
How do iodine tablets work?
If the body has all the iodine it needs, it will not absorb further iodine from
the atmosphere. The tablets fill the body up with non-radioactive iodine, which
prevent it absorbing the radioactive iodine.
What kind of radiation levels have been recorded at Fukushima?
The Kyodo news agency reports that a radiation level of 1,557 microsieverts per
hour was registered on Sunday. At this level, one hour's exposure is roughly
equivalent to one chest X-ray. Later measurements included 750 microsieverts per
hour at 0200 on Monday, and 20 microsieverts per hour at 1145. On a long-haul
flight, passengers are exposed to about five microsieverts per hour. However,
after Tuesday's explosion, readings at the site rose again beyone safe limits -
400 millisieverts per hour and people living within 20 miles (32km) of the plant
were told to stay indoors. Moving away from the source of radiation,
measurements quickly tail off, and in Tokyo they were reported to have been
higher than normal, but officials said there were no health dangers.
Is any level of exposure to radiation safe?
In some parts of the world, natural background radiation is significantly higher
than others - for example in Cornwall, in south-west England. And yet people
live in Cornwall, and many others gladly visit the area. Similarly, every
international air flight exposes passengers to higher than normal levels of
radiation - and yet people still fly, and cabin crews spend large amounts of
time exposed to this radiation. Patients in hospitals regularly undergo X-rays.
Scientists dispute whether any level of exposure to radiation is entirely safe,
but exposure to some level of radiation - whether at normal background levels or
higher - is a fact of life.
How do Fukushima's problems affect the rest of the world?
It depends on how much radiation is released. At present, the IAEA says the
effects are of a "local" nature.
Health effects of radiation
What are the immediate health effects of exposure to radiation?
Exposure to moderate levels of radiation - above one gray - can result in
radiation sickness, which produces a range of symptoms.
Nausea and vomiting often begin within hours of exposure, followed by diarrhoea,
headaches and fever.
After the first round of symptoms, there may be a brief period with no apparent
illness, but this may be followed within weeks by new, more serious symptoms.
At higher levels of radiation, all of these symptoms may be immediately
apparent, along with widespread - and potentially fatal - damage to internal
organs.
Exposure to a radiation dose of four gray will typically kill about half of all
healthy adults.
For comparison, radiation therapy for cancer typically involves several doses of
between one and seven gray at a time - but these doses are highly controlled,
and usually specifically targeted at small areas of the body.
Radiation dose Effect
2 mSv/yr (millisieverts per year) Typical background radiation experienced by
everyone (average 1.5 mSv in Australia, 3 mSv in North America)
9 mSv/yr Exposure by airline crew flying New York-Tokyo polar route
20 mSv/yr Current limit (averaged) for nuclear industry employees
50 mSv/yr Former routine limit for nuclear industry employees. It is also the
dose rate which arises from natural background levels in several places in Iran,
India and Europe
100 mSv/yr Lowest level at which any increase in cancer is clearly evident.
350 mSv/lifetime Criterion for relocating people after Chernobyl accident
1,000 mSv single dose Causes (temporary) radiation sickness such as nausea and
decreased white blood cell count, but not death. Above this, severity of illness
increases with dose
5,000 mSv single dose Would kill about half those receiving it within a month
How is radiation sickness treated?
The first thing to do is to try to minimise further contamination by removing
clothes and shoes, and gently washing the skin with soap and water.
Drugs are available that increase white blood-cell production to counter any
damage that may have occurred to the bone marrow, and to reduce the risk of
further infections due to immune-system damage.
There are also specific drugs that can help to reduce the damage to internal
organs caused by radioactive particles.
How does radiation have an impact on health?
Radioactive materials that decay spontaneously produce ionising radiation, which
has the capacity to cause significant damage to the body's internal chemistry,
breaking the chemical bonds between the atoms and molecules that make up our
tissues.
The body responds by trying to repair this damage, but sometimes it is too
severe or widespread to make repair possible. There is also a danger of mistakes
in the natural repair process.
Regions of the body that are most vulnerable to radiation damage include the
cells lining the intestine and stomach, and the blood-cell producing cells in
the bone marrow.
The extent of the damage caused is dependent on how long people are exposed to
radiation, and at what level.
Radiation and cancer
· Most experts agree even small doses of ionising radiation - as low as
100 millisieverts - can increase the risk of cancer, but by a very small amount.
· In general, the risk of cancer increases as the dose of radiation
increases. Exposure to one sievert of radiation is estimated to increase the
lifetime risk of fatal cancer by around 5%.
· The thyroid gland and bone marrow are particularly sensitive to
ionising radiation.
· Leukemia, a type of cancer that arises in the bone marrow, is the most
common radiation-induced cancer. Leukemias may appear as early as a few years
after radiation exposure.
· Other cancer can also result from exposure to radiation, but may not
develop for at least a decade. These include cancers of the lung, skin, thyroid,
breast and stomach.
What are the most likely long-term health effects?
Cancer is the biggest long-term risk. Usually when the body's cells reach their
"sell-by date" they commit suicide. Cancer results when cells lose this ability,
and effectively become immortal, continuing to divide and divide in an
uncontrolled fashion.
The body has various processes for ensuring that cells do not become cancerous,
and for replacing damaged tissue.
But the damage caused by exposure to radiation can completely disrupt these
control processes, making it much more likely that cancer will result.
Failure to properly repair the damage caused by radiation can also result in
changes - or mutations - to the body's genetic material, which are not only
associated with cancer, but may also be potentially passed down to offspring,
leading to deformities in future generations. These can include smaller head or
brain size, poorly formed eyes, slow growth and severe learning difficulties.
Are children at greater risk?
Potentially yes. Because they are growing more rapidly, more cells are dividing,
and so the potential for things to go wrong is greater.
Following the Chernobyl nuclear reactor accident in the Ukraine in 1986, the
World Health Organization recorded a dramatic increase in thyroid cancer among
children in the vicinity.
This was because the radioactive materials released during the accident
contained high levels of radioactive iodine, a material that accumulates in the
thyroid.
What risk does Fukushima pose currently?
The Japanese authorities have recorded a radiation level of up 400 millisieverts
per hour at the nuclear plant itself.
A sievert is essentially equivalent to a gray, but tends to be used to measure
lower levels of radiation, and for assessing long-term risk, rather than the
short-term acute impact of exposure.
Professor Richard Wakeford, an expert in radiation exposure at the University of
Manchester, said exposure to a dose of 400 millisieverts was unlikely to cause
radiation sickness - that would require a dose of around twice that level (one
sievert/one gray).
However, it could start to depress the production of blood cells in the bone
marrow, and was likely to raise the lifetime risk of fatal cancer by 2-4%.
Typically, a Japanese person has a lifetime risk of fatal cancer of 20-25%.
Prof Wakeford stressed only emergency workers at the plant were at risk of
exposure to such a dose - but it was likely that they would only be exposed for
short periods of time to minimise their risk.
The level of exposure for the general population, even those living close to the
plant, was unlikely to be anywhere near as high.
How can the Japanese authorities minimise the cost to human health?
Prof Wakeford said that provided the Japanese authorities acted quickly, most of
the general population should be spared significant health problems.
He said in those circumstances the only people likely to be at risk of serious
health effects were nuclear workers at the plant or emergency workers exposed to
high levels of radiation.
He said the top priority would be to evacuate people from the area and to make
sure they did not eat contaminated food. The biggest risk was that radioactive
iodine could get into their system, raising the risk of thyroid cancer.
To counter that risk, people - in particular children - could be given tablets
containing stable iodine which would prevent the body absorbing the radioactive
version.
The Japanese already have a lot of iodine in their natural diet, so that should
help too.
How does Fukushima compare to Chernobyl?
Professor Gerry Thomas, who has studied the aftermath of the Chernobyl disaster,
said: "It is very unlikely that this will turn into anything that resembles
Chernobyl.
"In Chernobyl you had a steam explosion which exposed the reactor core, which
meant you had a lot of radiation shooting up into the atmosphere."
Prof Thomas said although the Chernobyl disaster had led to a rise in thyroid
cancer cases, the only people affected were those living in the immediate area
of the explosion and who were young at the time.
