Passive Neutron Albedo Reactivity with Fission Chambers

Passive Neutron Albedo Reactivity with Fission Chambers is oneof the instruments being researched by the Next Generation SafeguardInitiative Spent Fuel Nondestructive Assay Project. The instrumentuses neutrons generated from within the spent fuel assembly,mainly from Cm, to interrogate the assembly by reflectingthe neutrons back into the assembly. Two measurements are takenof the assembly, one of which has a Cd sleeve between the instrumentand the assembly and the other does not; the ratio of thesetwo measurements is correlated to the fissile content in the assembly.This current publication updates results published by Conlinet al. In particular the optimization of the cadmium liner length,improvements to the weighting constants used in determining the239Pueff mass are described. The improvements to the weightingconstants involved removing an absorption term and utilization ofa new capability added to the MCNPX code called “First Fission.”