A fast-neutron coincidence collar using liquid scintillators for fresh fuel verification

The IAEA has developed a liquid scintillator-based system for the non-destructive assay of 235U in fresh fuel assemblies. The fast neutron coincidence collar (FNCL) addresses current limitations in existing neutron coincidence counting techniques when measuring fuel containing burnable neutron poisons. Detection of fast neutrons rather than thermal neutrons allows the minimisation of measurement time and biases (due to effects of burnable poisons). The FNCL hardware, software and instrument optimisation are discussed. Experimental results from measurements of mock-up uranium fuel assemblies at the institute for transuranium elements, Karlsruhe, Germany with varying 235U enrichment and burnable neutron poison content are presented.