Year
2018
Abstract
The verification of the 235U mass in fresh fuel assemblies for Light Water Reactors (LWR) is needed for international safeguards and accountability. For more than three decades, the IAEA has used the Uranium Neutron Coincidence Collar (UNCL) for this purpose, where thermal-neutron interrogation by an AmLi source is used to verify 235U content in the fuel assemblies. The high thermal neutron absorption by burnable poisons in LWR fuel complicates neutron verification measurements. Current techniques rely on either operator declarations of the burnable poison content to correct for the thermal neutron absorption of the burnable poisons, or long “fast mode” measurements of the fuel with a Cd liner. Several research programs have attempted to solve this problem through the development of novel measurement technologies. For the present paper, using Monte Carlo modeling, we have developed an advanced analytical technique to simultaneously determine both the 235U content and the burnable poison content in the fuel. This new analytical development has the important operational benefit of being able to verify the 235U mass without any operator-supplied information related to the burnable poison. Also, the method can be applied to existing UNCL hardware as well as future detector systems.