Energy production, radiation emission, induced radioactivity and irradiation damage

ENERGY PRODUCTION, RADIATION EMISSION, INDUCED RADIOACTIVITY AND IRRADIATION DAMAGE 

Actinide decay heat. The actinide decay heat at short times following the shut-down of a power reactor arises predominantly from the decay of U-239 (1.410 secs) and Np-239 (2x 10 secs). This component varies with fuel bum-up because of the variation of the number of U-238 captures per fission. Alpha decay of Cm-242 (1.41 x lO secs) makes a significant contribution to the decay heat at longer decay times. This arises from neutron capture in Am-241 produced by the decay of Pu-241 (14.6 year). The fraction of Am-241 in the fuel depends on the length of time for which it was stored between the abstraction of plutonium from irradiated fuel and the loading of the plutonimn into the reactor, and also the reactor residence time. 

Structural material decay heat. Heat is generated in the steels of the fuel pin cladding and the subassembly wrapper of a fast reactor fuel subassembly by the decay of radioactive products. This component of the decay heat does not exceed 10% of the total decay heat at any time. Integral measurements have been made of the activity induced in structural materials and these enable this component to be predicted to an accuracy of about 10% 

Only about 3% of the energy is deposited outside the fuel and about a half of this is deposited in the fuel cladding. 

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