fukushima: public safety - university of manchester · fukushima: public safety will it be like...
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Fukushima: Public SafetyWill it be Like Chernobyl?
There are big differences. Chernobyl was a totally different reactor design without a containment vessel at all. The
reactor itself exploded and the graphite in the reactor then burned. The Fukushima reactors have not themselves
exploded, do not contain any flammable graphite, and have two layers of containment. Given the fundamental
differences between these reactors and Chernobyl, and also that several days have now passed since the start of the
accident, it is very difficult to see any way in which a Chernobyl-like explosion will occur.
Is it Harmful to Health?
The amounts of radioactivity dispersed off site so far are
really very small and will not add significantly to the
radiation exposure arising from natural sources. If things
get significantly worse, then that could change and this is get significantly worse, then that could change and this is
why the Government has ordered evacuation of the
population up to 20 km from the plant. This seems a wise
precaution, particularly as travel may well be difficult due
to earthquake/tsunami damage and it might be
impossible to evacuate in a hurry.
Radiation Doses and effects provided by the World Nuclear Association
Radiation Dose Effect
2 millisieverts per
year (mSv/yr)
Typical background radiation experienced by everyone
(average; e.g. 1.5 mSv in Australia 3 mSv in North America
[see Figure 1]).
Up to 5 mSv/yr Typical incremental dose for aircrew in middle latitudes.
9 mSv/yr Exposure by airline crew flying the New York – Tokyo polar
route.
15 mSv single
dose
Effective dose of a CT scan of the abdomen and pelvis.
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. Above this, the probability of cancer occurrence
(rather than the severity) increases with dose.
1000 mSv single
dose
Causes (temporary) acute symptoms, also known as
radiation sickness. These include nausea and decreased
white blood cell count, but not death. Above this, severity of
How are the Volatile Radioisotopes Being Managed?
The most effective way to protect people from radiation is to
move them away from it, this is why the area surrounding the
Fukushima plant has been evacuated to a radius of 20 km.
The Japanese Ministry of Education, Culture, Sports, Science
and Technology (MEXT) is responsible for monitoring the dose
outside of the exclusion zone in order to ensure evacuation to
this distance is sufficient.
As previously stated, iodine-131 is one of the first
radioisotopes to breach containment in a loss of coolant
incident due to its high volatility. The physiology of iodine is
such that it accumulates in the thyroid, a tissue prone to
cancers. This is a hazardous combination as the significant
increase in thyroid cancers in children following the
People and animals alike are monitored on leaving the exclusion zone to ensure
that they are free of contamination.
Figure 1: Graph of the
average annual doses
from natural radiation sources in a variety of
countries. Notice how the
total amount of radiation and the sources releasing
it vary dramatically
between countries due to changes in local geology
and global location.
Provided by World Nuclear Organisation.
white blood cell count, but not death. Above this, severity of
illness increases.
5000 mSv single
dose
Would kill about half those receiving it within a month.
References
• www.world-nuclear.org , Chernobyl Accident.
• World Nuclear News, Regulation and Safety.
On the Fukushima site itself, radiation doses are much
higher and, in some places at some times, they are too
high to allow workers to stay in the area. That is why, on
occasion, workers have been evacuated from the site, and
the workforce is being used in short shifts to limit their
exposure. Their exposure will also be monitored carefully.
Considering the persistent levels of radiation observed on
site (between planned venting events), acute symptoms
are unlikely (‘radiation sickness’) , but any radiation
exposure brings an increased risk of illness like cancer in
later life. The risk can be related directly to the radiation
dose, and this is why the workforce doses are monitored
so closely, to ensure that they do not incur an
unacceptably high risk. The doses away from the site carry
negligible risk of such illness, below one in a million.
increase in thyroid cancers in children following the
Chernobyl incident demonstrates1. On the 12 March, the
Japanese government began to distribute non-radioactive
potassium iodide supplements to citizens2. These
supplements prevent accumulation of iodine-131 in the
thyroid by ensuring the body contains all the iodine it needs,
so any iodine-131 inhaled/ingested is quickly excreted, rather
than accumulated.