APPLICATION OF THE GRAVIMETRIC METHOD TO CLOSING THE MATERIAL BALANCE AROUND THE CHOP-LEACH CELL OF A SPENT-FUEL REPROCESSING PLANT

For a spent-fuel reprocessing plant handling commercial light-water-reactor fuel, plutonium accounting is traditionally done for the material balance area (MBA) extending from the input accountability tank to the product accountability tank - the process MBA. Consider an MBA comprising the chop—leach cell, with an inward flow consisting of the intact spent-fuel assemblies and outward flows consisting of leached hulls and dissolver solution. Given knowledge of the original uranium mass in the fuel and a measurement of the uranium-plutonium concentration ratio in the dissolver solution, the gravimetric method can be used to determine the amount of plutonium in the spent-fuel assemblies. A measurement of residual plutonium in the leached hulls would then permit the determination of a plutonium material balance for the chop-leach cell alone, since the volumetrically determined plutonium in the input accountability tank yields the plutonium in the flow leaving the chop-leach cell for the process MBA. The uncertainty in the balance can be estimated given the individual measurement uncertainties.