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Probability of severe nuclear accidents every 10 – 20 years

The computer simulations revealed that, on average, only eight percent of the 137Cs particles are expected to deposit within an area of 50 kilometres around the nuclear accident site. Around 50 percent of the particles would be deposited outside a radius of 1,000 kilometres, and around 25 percent would spread even further than 2,000 kilometres.
These results underscore that reactor accidents are likely to cause radioactive contamination well beyond national borders.

If a single nuclear meltdown were to occur in Western Europe, around 28 million people on average would be affected by contamination of more than 40 kilobecquerels per square meter. This figure is even higher in southern Asia, due to the dense populations. A major nuclear accident there would affect around 34 million people, while in the eastern USA and in East Asia this would be 14 to 21 million people.

Severe Nuclear Reactor Accidents Likely Every 10 to 20 Years, European StudySuggestshttp://www.sciencedaily.com/releases/2012/05/120522134942.htm ScienceDaily (May 22, 2012)— Western Europe has the worldwide highest risk of radioactive contamination caused by major reactor accident. Catastrophic nuclear accidents such as the core meltdowns in Chernobyl and Fukushima are more likely to happen than previously assumed.

Based on the operating hours of all civil nuclear reactors and the number of nuclear meltdowns that have occurred, scientists at the Max Planck Institute for Chemistry in Mainz have calculated that such events may occur once every 10 to 20 years (based on the current number of reactors) — some 200 times more often than estimated in the past.

The researchers also determined that, in the event of such a major accident, half of the radioactive caesium-137 would be spread over an area of more than 1,000 kilometres away from the nuclear reactor. Their results show that Western Europe is likely to be contaminated about once in 50 years by more than 40 kilobecquerel of caesium-137
per square meter. According to the International Atomic Energy Agency, an area is defined as being contaminated with radiation from this amount onwards. In view of their findings, the researchers call for an in-depth analysis and reassessment of the risks associated with nuclear power plants.

The reactor accident in Fukushima has fuelled the discussion about
nuclear energy and triggered Germany’s exit from their nuclear power
program. It appears that the global risk of such a catastrophe is
higher than previously thought, a result of a study carried out by a
research team led by Jos Lelieveld, Director of the Max Planck
Institute for Chemistry in Mainz: “After Fukushima, the prospect of
such an incident occurring again came into question, and whether we
can actually calculate the radioactive fallout using our atmospheric
models.” According to the results of the study, a nuclear meltdown in
one of the reactors in operation worldwide is likely to occur once in
10 to 20 years. Currently, there are 440 nuclear reactors in
operation, and 60 more are planned.
To determine the likelihood of a nuclear meltdown, the researchers
applied a simple calculation. They divided the operating hours of all
civilian nuclear reactors in the world, from the commissioning of the
first up to the present, by the number of reactor meltdowns that have
actually occurred.
The total number of operating hours is 14,500 years, the number of
reactor meltdowns comes to four — one in Chernobyl and three in
Fukushima. This translates into one major accident, being defined
according to the International Nuclear Event Scale (INES), every 3,625
years. Even if this result is conservatively rounded to one major
accident every 5,000 reactor years, the risk is 200 times higher than
the estimate for catastrophic, non-contained core meltdowns made by
the U.S. Nuclear Regulatory Commission in 1990. The Mainz researchers
did not distinguish ages and types of reactors, or whether they are
located in regions of enhanced risks, for example by earthquakes.
After all, nobody had anticipated the reactor catastrophe in Japan.
25 percent of the radioactive particles are transported further than
2,000 kilometres
Subsequently, the researchers determined the geographic distribution
of radioactive gases and particles around a possible accident site
using a computer model that describes Earth’s atmosphere. The model
calculates meteorological conditions and flows, and also accounts for
chemical reactions in the atmosphere. The model can compute the global
distribution of trace gases, for example, and can also simulate the
spreading of radioactive gases and particles. To approximate the
radioactive contamination, the researchers calculated how the
particles of radioactive caesium-137 (137Cs) disperse in the
atmosphere, where they deposit on Earth’s surface and in what
quantities. The 137Cs isotope is a product of the nuclear fission of
uranium. It has a half-life of 30 years and was one of the key
elements in the radioactive contamination following the disasters of
Chernobyl and Fukushima.
The computer simulations revealed that, on average, only eight percent of the 137Cs particles are expected to deposit within an area of 50 kilometres around the nuclear accident site. Around 50 percent of the particles would be deposited outside a radius of 1,000 kilometres, and around 25 percent would spread even further than 2,000 kilometres.
These results underscore that reactor accidents are likely to cause radioactive contamination well beyond national borders.
The results of the dispersion calculations were combined with the
likelihood of a nuclear meltdown and the actual density of reactors
worldwide to calculate the current risk of radioactive contamination
around the world. According to the International Atomic Energy Agency
(IAEA), an area with more than 40 kilobecquerels of radioactivity per
square meter is defined as contaminated.
The team in Mainz found that in Western Europe, where the density of
reactors is particularly high, the contamination by more than 40
kilobecquerels per square meter is expected to occur once in about
every 50 years. It appears that citizens in the densely populated
southwestern part of Germany run the worldwide highest risk of
radioactive contamination, associated with the numerous nuclear power
plants situated near the borders between France, Belgium and Germany,
and the dominant westerly wind direction.
If a single nuclear meltdown were to occur in Western Europe, around 28 million people on average would be affected by contamination of more than 40 kilobecquerels per square meter. This figure is even higher in southern Asia, due to the dense populations. A major nuclear accident there would affect around 34 million people, while in the eastern USA and in East Asia this would be 14 to 21 million people.
“Germany’s exit from the nuclear energy program will reduce the
national risk of radioactive contamination. However, an even stronger
reduction would result if Germany’s neighbours were to switch off
their reactors,” says Jos Lelieveld. “Not only do we need an in-depth
and public analysis of the actual risks of nuclear accidents. In light
of our findings I believe an internationally coordinated phasing out
of nuclear energy should also be considered ,” adds the atmospheric
chemist.

May 23, 2012 - Posted by Christina Macpherson | 2 WORLD, safety