Low-level Transuranic Waste Assay by Photon Interrogation and Neutron Counting

A comprehensive programme is currently in progress at several laboratories for the development of sensitive, practical, non destructive assay techniques for the quantification of low- level transuranics (TRU) in bulk solid wastes. Tliis report describes the method being developed to assay high density TRU waste packages using photon interrogation. The system uses a pulsed electron beam from a linear accelerator (LINAC) to produce high-energy photon bursts from a metallic converter. The photons induce fissions in TRU. When fission is induced in trace amounts of TRU contaminants in waste material, it provides \"signatures\" from fission products that can be used to assay the material before disposal. We give here the results from counting photofission-induced delayed neutrons from 239 Pu, 235 U and 238 U in sample matrices. We counted delayed neutrons emitted after each pulse of the LINAC. This enhances the available counts by a factor about 20 compared with the counting of delayed neutrons only after the irradiation period. The electron linear accelerator operates at 15 MeV, 140 mA, and 2.5 us wide pulse at a 50 Hz rate. The dynamics of photofission and delayed neutron production, use of an electron linear accelerator as a particle source, experimental and electronics details, and a future experimental works are discussed.