DELAYED NEUTRON METHOD FOR MEASUREMENT OF FISSILE/FERTILE CONTENT OF SAMPLES RANGING FROM ENVIRONMENTAL TO IRRADIATED FUEL

A delayed-neutron assay method is described which is capable of accurately determining the 2350 and 2380 contents of a wide range of materials. The method consists of irradiation in the Coupled Fast Reactivity Measurement Facility (CFRMF) at the Idaho National Engineering Laboratory (INEL), one position in the thermal driver area for 2350 assay, and a fast neutron flux position for 2380< After irradiation, delayed neutron counting is used to measure the uranium content of the sample. By utilizing fast and thermal neutron irradiation and counting cycles, the samples 2380 and 2350 contents are determined. Minimal sample preparation and handling is required to obtain accurate results. The method has been used successfully on a wide range of samples, including environmental (soil) samples, irradiated and unirradiated fuel, and debris from the Three Mile Island Unit II Reactor core. Measurement precision of up to 0.5Z can be achieved; sensitivity for low level samples is 9 counts counts mm mm -1 nanogram\"1 for 2350 and 0.02 —1 Ti«tiftarnTn~l for 380^ The contents of samples 240pu> 237Np> or by the same method, to nanogram fissile and/or fertile containing 233U, 239pUj 232fh could be determined Data from representative samples are presented illustrate the usefulness of these techniques.