Development of an asymmetric multiple-position neutron source (AMPNS) method to monitor the criticality of a degraded reactor core

An analytical/experimental method has been developed to monitor the subcritical reactivity and unfold the ksub(infinity) distribution of a degraded reactor core the method uses several fixed neutron detectors and a 252Cf neutron source placed sequentially in multiple positions in the core. Therefore, it is called the asymmetric multiple-position neutron source (AMPNS) method. The AMPNS method employs the nucleonic codes to analyze in two dimensions the neutron multiplication of a 252Cf neutron source. An optimization program, GPM, was utilized to unfold the ksub(infinity) distribution of the degraded core, in which the desired performance measure minimizes the error between the calculated and the measured count rates of the degraded reactor core. The analytical/ experimental approach is validated by performing experiments using the Penn. State Breazeale TRIGA reactor (PSBR). A significant result of this study has been to provide a means to plan the source and detector placements and assign core cells to the damaged TMI-2 core as well as to monitor the criticality during the recovery period. (author)