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The degree of core damage in the Japanese nuclear reactors

Dear Reader,

I hold the view that the way in which nuclear fuel behaves during an accident is not simple, and it has a great effect on the way in which an accident progresses (or does not progress).

In the ideal world the radioactivity inside a nuclear fuel will stay locked inside the fuel like a dangerous criminal locked in their cell. Sadly during an accident some effects can liberate the radioactivity from its prison cell.

One reaction which I consider to be important is the reaction of zirconium (the tubing used for covering most reactor fuel) with water, this is a reaction where the water oxidises the zirconium to form zirconium dioxide and hydrogen. Under normal aqueous oxidising conditions titanium and zirconium are passive because they have an oxide layer which prevents any further reaction. But at high temperatures steam, oxygen and hydrogen can react with zirconium alloys. For details please see the following documents.

http://parrinst.com/doc_library/dealer/Zircon.pdf

http://parrinst.com/doc_library/dealer/Titanium.pdf

Another important reaction is the thermite like reaction between uranium dioxide and zirconium tubing, this reaction was observed at Chernobyl. In a paper by B.E. Burakov, E.B. Anderson, B.Y. Galkin, E.M. Pazukhin, and S.I. Shabalev, Radiochimica Acta, 1994, volume 65, pages 199-202 they use the evidence created by this reaction (uranium zirconium oxide) that shows that the fuel at Chernobyl reached 2500 to 2600 degrees centigrade.

These reactions damage the zirconium alloy tubing and in the latter case it helps the melting process.

The IAEA have stated that in unit one that TEPCO now think that 55 % of the fuel has been damaged, in unit two 35 % of the fuel has been damaged while in unit three 30 % of the fuel has been damaged. I sadly do not know what they mean by “damaged fuel”, it is not clear what the dividing line is between damaged and undamaged fuel is.

http://www.iaea.org/newscenter/news/tsunamiupdate01.html

I hope to be able to post my views on some of the other reactions which are likely to occur during an accident another day.

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