Monitoring Spent or Reprocessed Nuclear Fuel Using Fast Neutrons

Over the past few years a number of experiments have been carried out at LLNL with a scintillator array that has the ability to count individual MeV neutrons and -rays with nanosecond timing. It has been demonstrated that this array can be used to measure the statistical properties of the neutrons emitted in single fission chains. The multiple time scales over which these fission neutrons are correlated allow one to deduce quite a lot regarding the nature of the fissile assembly. In this paper we will describe how neutron correlations measured with a liquid scintillator array can be used to assay the amounts of fissile elements in reprocessed and spent nuclear fuels.