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Considerable alarm is being raised about the possibility of a second major accident occurring at Fukushima. In particular, people are worried about the spent fuel pool at reactor 4. This is a hundred feet above the ground in a collapsing building. Starting today, the operators, TEPCO, are trying to move the fuel rods out. Bloggers are warning that, if this goes wrong, radiation would circle the northern hemisphere, perhaps eventually killing all humans. It has been said that even moving to the southern hemisphere would only prolong a refugee’s life for a few months.
The reality is that worse has already happened because in the last half-century life on earth has survived the fallout from testing Atom bombs and Hydrogen bombs. Above-ground testing between 1945 and 1963 caused more radioactive pollution than Fukushima could. Additional deaths in the subsequent global cancer epidemic number 52 million (and counting).
In a new paper Chris Busby, Scientific Secretary of the European Committee on Radiation Risk, analyses the worst imaginable accident – one that (improbably) ejected all the radioactivity on the Fukushima site. He puts this into the context of weapons tests and Chernobyl.
The worst case scenario is a catastrophic fission explosion of the material in the Spent Fuel pool following some collapse of the building. If this explosion was violent enough to cause secondary fission explosions in each of the other reactors and fuel pools it could be equivalent to a fairly low energy but very dirty fission bomb. In this case the heavy material would be dispersed mainly to the local environment and to the Pacific Ocean, as has already happened. More volatile radionuclides and nanoparticles would travel 2000 miles or more and would be deposited in rainfall.
By contrast, the A-bombs and H-bombs caused radioactivity to be spread much more widely. The colossal energy of the nuclear tests vaporized all the materials in the bombs, including the heavy metals Uranium and Plutonium. The radioactivity dispersed all over the world and is still detectable in rainfall.
Analysed in terms of the volatile radio-elements Caesium137 and Strontium 90, the inventory of radioactivity in the fuel ponds and the damaged reactors is 60% of the radioactivity injected into the biosphere by weapons testing. The Fukushima sites now contain 80 times as much Caesium137 and Strontium 90 as were released in the first months of the emergency there. Fukushima contains 80 times as much Caesium137 and 260 times as much Strontium 90 as were ejected during the Chernobyl accident in 1986; it contains 10,000 times as much Caesium137 and Strontium 90 as were released by the Hiroshima bomb. If the worst happened at Fukushima Honshu (the north island) would be uninhabitable (some would say it already is). Doses to the public from Caesium 137 across Honshu would be 438 times higher than European law would allow. Other radio-elements would be present and would increase the exposure.
There is no cause for complacency about the effects in more distant regions; the very low concentrations of I-131 measured in California in 2011 caused a significant increase in hyperthyroidism in infants in California. Heritable genetic effects will follow and the general increase in cancer will continue, but the accident that could happen in Fukushima would not threaten mass extinction.
Background reading:A comparison of Fukushima emissions in 2011 with Chernobyl
How bad could the health effects be? Here is A paper in which measured fallout and cancer rates following Chernobyl were used to predict the cancer yield from Fukushima
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