Design of a New Passive Neutron Multiplication Counter to Improve Safeguards Verification of VVER-440 Fuel Assemblies

Year
2014
Author(s)
Howard O. Menlove - Los Alamos National Laboratory
Daniela Henzlova - Los Alamos National Laboratory
Adrienne M. Lafleur - Los Alamos National Laboratory
Michael C. Browne - Los Alamos National Laboratory
Colin Carroll - Brookhaven National Laboratory
Abstract
A new non-destructive assay (NDA) technique called Passive Neutron Multiplication Counter (PNMC) is currently being developed at Los Alamos National Laboratory (LANL) to improve safeguards measurements of VVER-440 fuel assemblies. The PNMC uses the ratio of the fast- neutron emission rate to the thermal-neutron emission rate to quantify the neutron multiplication of the item. The fast neutrons versus thermal neutrons are measured using fission chambers (FC) that have differential shielding to isolate fast and thermal energies. The fast-neutron emission rate is directly proportional to the neutron multiplication in the spent fuel assembly; whereas, the thermal-neutron leakage is suppressed by the fissile material absorption in the assembly. The basic design of this detector is essentially a modified FORK detector consisting of 4 fission chambers and 2 ion chambers. Monte Carlo N-Particle eXtended transport code simulations of the PNMC were performed to optimize the detector design and estimate the expected count rates for VVER-440 fuel assemblies. The detector hardware for the PNMC has been fabricated and we plan to perform experimental measurements of VVER-440 fuel assemblies at the Armenia Nuclear Power Plant (ANPP) in the summer of 2014. The results from these simulations and measurements will provide valuable experimental data that directly supports safeguards research and development (R&D) efforts on the viability of passive neutron NDA techniques and detector designs for safeguards measurements of spent fuel assemblies.