Transmuting minor actinides with thermal reactor neutrons
The process of closing natural U based nuclear fuel cycle presupposes extracting U and Pu from spent fuel. Among the remaining heavy nuclei the major contribution of radioactivity is due to minor actinides. One of the ideas suggested to reduce the radioactivity of spent fuel is to reradiate minor actinides for a longer period of time, such process being referred to as transmutation.
Some authors claim the necessity of transmutation in the high energy neutron spectra. To accomplish this the purpose oriented burner-reactors and accelerator-based sub critical systems are to be incorporated into nuclear fuel cycle
The particular paper considers feasibility of transmuting minor actinides with thermal reactor neutrons. Basic factor of transmutation feasibility – ratio of radioactivity levels with and without transmutation ξ(t) has been used. This ratio in function ξ(t) can be either more or less 1, the values making major contribution into the feasibility assessment. Functions ξ(t) for minor actinides have been calculated. The following conclusions have been made in terms of reducing radioactivity: (a) Ne is not a subject for transmuting; (b) a relatively small effect has been observed for Cm, its radioactivity reducing by an order in 500 years; © Am reduces its radioactivity from 10 to 100 times 300 years after being reradiated. The authors have shown that the best ξ(t) values are reached when minor actinides burn-up is up to 70–80%.
In order to come to a conclusion on transmutation feasibility for Am and Cm the authors suggest that in the scenarios involved the following issues be taken into account – how risks of their release into the environment differ, how biological effectiveness differs as well as efficiency of transmuting minor actinides produced by operating nuclear power and continuously placed into spent fuel storage.
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