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MOX use

I have noticed that in Japan a utility company (Kansai Electric Power Company) is having difficulty getting approval for the use of MOX in a power reactor. I hold a view that all reactors which are fueled with uranium dioxide soon end up running on a mixture of plutonium and uranium (MOX) as plutonium is made by the neutron activation of uranium-238.

So all power reactors which are in use should be able to cope with at least part of their fuel being MOX. I think that the horrors of nuclear warfare have changed the way that people view plutonium. As plutonium-239 has been many bomb maker’s fuel of choice for years people associate all plutonium with death and bombs.

The use of MOX in a power reactor in your city will not help the production of atom bombs, if anything it will do the reverse.

The use of bomb grade plutonium in power reactors is good for world peace as the plutonium breed in these reactors will be far less suitable for building a bomb than the plutonium which went into the original MOX. The build up of Pu-240 in MOX which has been recycled several times will turn what is a bombmaker’s dream plutonium into a plutonium which is close to their worst nightmare. Also the build up of Pu-241 will make it harder to build bombs which have long shelf lives.

The MOX will not make the reactor any more dangerous as long as the amount of plutonium is not too large in the reactor. The ratio of prompt to delayed neutrons for plutonium is different to uranium. So as a result the control mechanisms for a reactor running only on plutonium have to be able to work faster, but the speed of operation is within what modern engineering can manage.

During an accident like the Fukuashima accident the plutonium in the fuel is not mobile, very little of the radioactive release from the stricken plants in Japan has been plutonium. One of these plants was running on MOX.

Plutonium during an overheating accident is like a dragon which is encased in a deep cave, while the iodine is more like an angry dog snake hybrid which creeps into your house via the letter box. If you stay out of the cave you should be OK while the iodine monster can come and attack you when you are not expecting it.

I think that the mobile beta/gamma emitting fission products pose a far greater threat to public health than the plutonium will do. It is important to bear in mind that the addition of some plutonium to uranium dioxide will not have a dramatic effect on the melting point of the mixed oxide. The addition of the plutonium does not disrupt the crystal lattice as uranium and plutonium dioxide have exactly the same structures, they form a solid solution, so a MOX fueled reactor will not be more prone to meltdowns.

Also a man in Japan (Akihide Hidaka) published a paper recently on the results of some experiments where real used UO2 and MOX fuels were subjected to a simulation of an overheating accident just like Fukuashima. This was in the Journal of Nuclear Science and Technology, 2011, volume 48, pages 85 to 102. He showed that during an overheating accident that MOX is no more dangerous to the public than normal UO2 fuel.


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