Posted by: Mark Foreman | August 12, 2015

Nulcear restart in Japan

Dear Reader,

It has come to my attention that a utility company in Japan have restarted a power reactor, now I know that a lot of people are very displeased about this saying that it is unsafe. But I have a question, after the Fukushima event the power reactors in Japan were shut down, now I imagine that some other fuel was used to provide the electric power while the reactors were shut down.

When people say that “nuclear is unsafe” do they consider the degree of harm caused by the alternative fuel or not ? A quick look at the EIA in the US suggests that after Fukushima that Japan was using coal, oil and gas to provide electrical power. As coal ash is often radioactive and as the oil / gas industry also are producers of radioactive waste. I have to ask the question of did the closure of the power reactors in Japan result in higher worker and public doses.

While the shutdown of a reactor might lower the doses of some people, the increased need for coal / oil might increase the doses of another group of people. What would be interesting is to find out what happened to the collective dose for the whole of the world’s population as a result of the closure of the Japanese power reactors.

I hold the view that the majority of the radioactivity which nuclear power plants generate is short-lived beta/gamma, while more activity (in Bq) might be produced per joule of electrical power delivered to the public than is handled during the use of a fossil fuel. If we take the view of how much activity will be released by the plant then the nuclear plant has a bit of an advantage that the radioactive waste is far better contained.

We also in our exposure assessment need to consider the fact that the longer half-lives of things like radium-226 in fly ash makes a release of it more serious than a release of the same activity of shorter lived fission products such as krypton-85. We also need to consider how the longer lived radionuclides from fossil fuel tend to be alpha emitters while the nuclear power fission products tend to be beta emitters, the alpha emitters might be short ranged but the internal threat they pose tends to be far higher than that posed by beta emitters.

Also the geochemistry and biochemistry of radium and its daughters increases the threat posed, much of the alpha activity in the back-end of the nuclear fuel cycle is plutonium. Plutonium is not very mobile in soil water and the human digestive system is not very able to absorb plutonium. On the other hand radium is quite mobile, radon is very mobile and the human digestive system is rather good at absorbing radium.

We also need to bear in mind that the use of fossil fuels can result in air pollution. Has this been considered in the judgement of nuclear as being unsafe ?

Also I know that MOX use has been demonized by some persons, but let us consider again the overall effect of MOX use. It is important to consider the whole rather than concentrating on a single part. For example it has been shown by one group in the USA that in terms of chemical toxicity to soil bacteria that plutonium is close to non toxic and that the alpha activity of the plutonium has no effect on the bacteria. They used both short-lived and long-lived plutonium to test the hypothesis that the plutonium only has a chemical effect on the bacteria.

If we were to use this study as our only source of information about plutonium we would come to the unreasonable conclusion that plutonium is harmless to humans. But back to the MOX question.

If MOX is used then the amount of alpha activity in the back end of the fuel cycle will increase, this alpha activity will be mostly in the form of plutonium, americium, curium and other long lived transuranium elements. A small increase in uranium-232 will occur but the alpha activity associated with this will be small compared with the transuranium elements. As the plutonium and the other transuraniums tend to be in high oxidation states they will tend to be not very mobile in soil water. The plutonium is likely to be as Pu(IV) while the americium / curium etc will be as Am(III) and Cm(III). These very highly charged cations will undergo plenty of hydrolysis and also tend to stick to mineral surfaces when the water is neutral or alkaline. Also once plutonium(IV) forms a solid it is very hard to redissolve, one of the enduring problems in the nuclear reprocessing sector is the fact that it is very hard to dissolve high plutonium content MOX fuels in nitric acid.

On the other hand the use of MOX will result in less uranium mining and less alpha emitting waste in the front end of the fuel cycle. The front end alpha waste will include the more mobile and toxic radium. The front end of the fuel cycle also is associated with human exposure to radon which is a problem which is less likely to appear in the back-end of the fuel cycle. But I note that inside the Chernobyl object shelter that the radon-220 (thoron) levels are rather high, so I would never say never. But compared with the other radioactive issues in a reprocessing plant the radon-222 and radon-220 will normally be small matters.

So while MOX use might form more alpha waste from a drinking water / ground water point of view the alpha waste problem could be mitigated by moving to MOX use.

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