| Summary: | Nuclear waste is a highly debated issue of nuclear power. The long-term storage is not considered to be sustainable, thus other possibilities are sought after. One such possibility could be to recycle the nuclear waste in nuclear reactors, such as fast breeder reactors. The possibility to recycle americium, which is a nuclear waste, is the reason of this study. This report studies how the amount of americium in the fuel of the reactor ELECTRA affects the temperature coefficient. It was also examined how the size of the reactor affects the reactivity factor, k eff. The purpose was to see how much americium that could be added to the fuel before the temperature coefficient becomes positive, and the reactor becomes unstable. The results first obtained in the study were not as expected. The expected result was that with an increased amount of americium the temperature coefficient would also increase. Instead the value of the temperature coefficient remained at an almost constant level. This is assumed to be because the reactor is designed to have a high amount of neutron leakage, which dominates the impact on the temperature coefficient. To decrease the impact of the neutron leakage and to maintain criticality, the height of the reactor core was increased. This lead to the expected results of an increased temperature coefficient with an increased amount of americium in the fuel. The study also shows that more fuel is needed to maintain criticality when more americium is added.
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