A simple approximation to estimate the reactor period in critical assemblies

A simple approximation is proposed to estimate the reactor period in critical assemblies for which the reactivity parameters, such as the fissile material, neutron-energy spectrum, and effective fraction of delayed neutrons, are characterized. This approximation is based on the period-reactivity equation, in combination with the delayed-neutron parameters corresponding to the fissile material and neutron-energy spectrum of the critical assembly, and Monte Carlo computer-code calculations of the criticality factor, prompt-neutron lifetime, and average number of neutrons per fission. The proposed approximation is validated with experimental results for the Lady Godiva fast metal and the Solution-High Energy Burst Assembly (SHEBA) thermal solution critical assemblies that operated at Los Alamos National Laboratory. In addition, the results of the approximation are also compared with those reported for experiments conducted at the Kyoto University Critical Assembly. The results from this analysis indicate that the proposed approximation can be used to estimate the reactor period in critical assemblies.