On the prompt time eigenvalue estimation for subcritical multiplying systems

Kinetics experiments are carried out in subcritical systems in order to estimate the subcriticality level. The reactivity is reconstructed from neutron flux measurements obtained by local neutron detectors. In this paper a method to reconstruct the prompt time constant for a subcritical system using flux measurements following a source pulse is presented. While the prompt time constant is by itself a significant characterization of the subcriticality level, it can also be used to reconstruct the system reactivity. The approach is based on Prony’s analysis, which is a standard method for non-linear minimization problems when only exponentials or sinusoids are involved. The problems connected to the presence of experimental errors are overcome by properly modifying the technique. The effects of experimental uncertainties and detector positioning is analyzed.