Application of a Self-Multiplication Correction Method to a Neutron Coincidence Counter and Its Calibration for Spent Fuel

A passive neutron coincidence counter was developed for the nondestructive measurements of the nuclear materials in the Advanced Spent Fuel Conditioning Process (ACP) facility at the Korea Atomic Energy Research Institute (KAERI). A hot test of the neutron counter was performed with spent fuel rod-cuts to obtain the calibration curve for ²⁴⁴Cm in 2007. The source terms were analyzed by using the ORIGEN-ARP code. There was a considerable difference in the neutron counting rates between the measurements and the MCNPX simulation results. This difference was systematic and came from the errors in the declared ²⁴⁴Cm mass obtained by using the burnup code. To correct the calibration curve, a self-multiplication correction method was applied, and the corrected singles and doubles rates as well as the expected ²⁴⁴Cm mass of each rod-cut were obtained as a result. The differences in the calibration constants between the measurements and the MCNPX results were - 33% and - 34% for the singles and doubles rates, respectively. However, those differences between the self-multiplication correction and MCNPX results were reduced to - 1% and - 5% for the singles and doubles rates, respectively.