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More isotope data from Japan

Dear Reader,

As promised I am going to share with you some of the isotope data which I have obtained from the NISA and the JAIF in Japan. I have looked at the data and I have come to some conclusions.

1. The uranium level in the soil close to the reactor is about the right range for a normal soil, and the isotope signature matches natural uranium. I think that if the majority of the uranium in the soil was from the nuclear fuel at the plant then the isotope signature would be different.

2. The transuranium actinides (Plutonium and curium) need to be considered. The level of the actinides (when the activities are normalised to make the Cs-137 levels the same) is much lower, this suggests to me that the level of damage to the nuclear fuel is much less in the Japanese accident than it was at Chernobyl. At the Chernobyl accident a nasty big steam explosion smashed the fuel into small fragments which were flung out of the reactor building. The Nb-95 : Cs-137 ratio at Fukuashima also suggests that the level of damage to the fuel is lower. The Zr-95 and Nb-95 isotopes are very important, this is because ZrO2 has very similar solid state chemistry to plutonium.

3. The lack of Mo-99, Tc-99m and Ru-106 in the release from Japan suggest to me that the fuel has been subject to less mechanical violence and heating in an oxygen rich environment. The Mo could form volatile MoO3 if it is heated in air, while the Ru can form RuO4 when it is heated in air.

4. The Sr : Cs ratios also suggest that at Fukuashima that the fuel has been damaged less, I think that the steam explosion at Chernobyl would have flung a lot of solid and less water soluble forms of strontium out of the reactor. This would have included the SrZrO3 phase which is present in used nuclear fuel. This SrZrO3 phase is the perovskite phase which is found in used uranium dioxide (and MOX) fuel.

Part of the isotope signatures of the Chernboyl and Fukuashima accidents

One of the things which I think should be done in Japan is that a sample of the soil with the radioactive contamination should be subjected to a series of chemical leaching.

Firstly the soil should be extracted with water, to extract the water soluble fission products which do not bind to soil minerals. Then the soil should be subject to a series of extractions, each extraction should be more harsh than the last. The idea of such an experiment is to get some idea of the chemical forms of the radioactive isotopes which are present in the fallout.

Rather than being a “waste of time experiment” the results of this experiment would help by giving clues on how the radioactvity will behave in the wide wide world. We need to know how easy it will be for the radioactivity to enter the food chain and thus endanger humans. The leaching rate of the solid particles of the fallout is very important, for example plutonium which is formed by neutron activation of uranium in an atom bomb is more soluble (and able to enter living things) than the plutonium in bomb fallout which was part of the plutonium used to build an atom bomb.


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