Prompt neutron lifetime in a strongly heterogeneous lattice

The prompt neutron lifetime is an important input parameter to the solution of the point reactor kinetics equations. In the past, many methods of determining the prompt neutron lifetime included the assumption that the thermal neutron lifetime was a good approximation to the prompt neutron lifetime. It has been found that strong heterogeneities within a lattice cause the calculation of the thermal neutron lifetime to significantly overpredict the prompt neutron lifetime. Therefore, a new method for the calculation of the prompt neutron lifetime is presented. This new method, the Alpha Search Method (ASM), is based on the time eigenvalue and does not suffer from the overprediction of the neutron lifetime as approximated by the thermal neutron lifetime. The causes of this overprediction, as well as comparisons of lifetimes computed by the ASM and other methods will be presented.