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Chernobyl and Fukuashima which is worse ?

Dear Reader, I recently was sent a rather long comment on the blog entry on the way in which TEPCO are going to deal with the mess in Japan.

This person wrote,

‘The IAEA will call Fukushima “not as bad as Chernobyl”

To allow us to understand what has happened, what is happening and what we should do we need to be able to compare the Fukushima event with other accidents, both nuclear and non-nuclear. The accident which many people are thinking about is Chernobyl, I would encourage people to also think about Bhopal, Aberfan and the Great Boston Molasses Tragedy . At Bhopal a toxic gas leak from a factory gassed out a city killing about 20000 people, at Aberfan a mining spoil head slide down a hill and killed 144 members of the public. The most horrible part of Aberfan that most of the dead (116) were primary school children who were killed inside their school. The Great Boston Molasses Tragedy killed 21 people who came to a very sticky end, they drowned in molasses.

Fukushima released about 10 times less radioactivity than the Chernobyl event in the month after the earth quake according to the following report.

http://www.nisa.meti.go.jp/english/files/en20110412-4.pdf

While another estimate puts the cesium release at between 20 and 60 % of the Chernobyl release.

http://www.zamg.ac.at/docs/aktuell/Japan2011-03-24_1600_E.pdf

Using my trusty vintage copy of the CRC handbook of chemistry and physics (the rubber book) I have looked up the intake limits for some isotopes.

For inhalation of water soluble forms of these isotopes the following three month limits existed back in the 1970s / 1960s.

Cs-137 40 microcuries

I-131 5.3 microcuries

Sr-90 0.73 microcuries

Pu-239 0.0011 microcuries

The way to understand these numbers is that the lower the number the more dangerous an isotope is to human health. It is clear that the strontium-90 is a more dangerous isotope than the iodine and cesium.

It is thought that at Chernobyl that 85 PBq of Cs-137 was released, while 10 PBq of Sr-90 was released (http://www.oecd-nea.org/rp/reports/2003/nea3508-chernobyl.pdf). While less of the strontium was released than cesium, it is clear that due to the much higher toxicity of the Sr-90 that for inhalation of the radioactive cloud from Chernobyl that the strontium posed a greater threat to human health.

Because the Japanese accident was a loss of cooling accident while Chernobyl was a reactivity accident which flung fuel particles into the air, the release from Fukuashima will be closer to a pure iodine / cesium release than the Chernobyl release. So as a result the accidents should be considered in very different ways. As the Sr/Cs ratios will be so different for the two accidents I hold the view that if the Cs-137 release of the two accidents was the same then Chernobyl would still be a bigger accident.

I am not alone in holding this view.

http://www.newscientist.com/blogs/shortsharpscience/2011/04/fukushima-crisis-raised-to-lev.html?DCMP=OTC-rss&nsref=online-news

Before anyone asks it is very hard to release plutonium from nuclear fuel (uranium dioxide or MOX) by simple heating, so in common with the strontium I would expect far less plutonium to escape from the plant for a given cesium release.

At Fukushima no steam explosions have occurred inside the reactors, as a result a large amount of radioactive used fuel has not been scattered over the reactor park. This absence of large lumps of used fuel makes the site less dangerous to the plant workers. So as a result I hold the view that the death toll due to acute effects among the plant workers will be likely to be zero. This difference is another reason why I think that the Japanese reactor accident is not as bad as Chernobyl.

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