Delayed Neutron Method for Measurement of Fissile/Fertile Content of Samples Ranging from Environmental to Irradiated Fuel

摘要

A delayed-neutron assay method is described which is capable of accurately determining the sup 235 U and sup 238 U 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 sup 235 U assay, and a fast neutron flux position for sup 238 U. 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 exp 238 U and sup 235 U contents are determined. Minimal sample preparation and handling are 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 0.5% can be achieved; sensitivity for low level samples is 9 counts min exp -1 nanogram exp -1 for sup 235 U and 0.02 counts min exp -1 nanogram exp -1 for exp 238 U. The fissile and/or fertile contents of samples containing sup 233 U, sup 239 Pu, sup 240 Pu, sup 237 Np, or sup 232 Th could be determined by the same method. Data from representative samples are presented to illustrate the usefulness of these techniques. (ERA citation 09:040672)