Subcritical Reactivity Monitoring: Neutron Yields from Spontaneous ( Alpha ,N) Reactions in FFTF Fuel

摘要

Neutron yields resulting from the reaction of alpha particles emitted by heavy metal isotopes with isotopes of oxygen are evaluated. The yields are evaluated for various alpha-decaying isotopes that are initially present or built up during irradiation in FFTF fuels. Calculations are performed using a sum of probabilities for exp 17 O( alpha ,n) exp 20 Ne and exp 18 O( alpha ,n) exp 21 Ne reactions in fuels which have been evaluated using basic nuclear data. The calculated yields are in agreement with those found in the literature except for the exp 242 Cm and exp 244 Cm isotopes of curium where the discrepancy is approximately one order of magnitude. The curium isotopes are present only in irradiated fuel and build up with increased irradiation. However, for exp 244 Cm the predominant contribution of neutrons to the total neutron source results from spontaneous fission rather than the ( alpha ,n) reactions of the alpha particles emitted by exp 244 Cm with oxygen. For exp 242 Cm, the discrepancy is more significant since previous evaluations of the ( alpha ,n) yield showed it to be comparable to the spontaneous fission yield. The method used for the calculation of the ( alpha ,n) reaction yields provide the most accurate neutron yield evaluation currently available with existing nuclear data. (ERA citation 03:047783)