Transuranic waste detection by photon interrogation and on-line delayed neutron counting

A comprehensive program is currently in progress at several laboratories fo r the development of sensitive, practical, non-destructive assay techniques for the quantification of low-level transuranics (TRUs) in bulk solid wast es. This paper describes the method being developed to assay high density TRU w aste packages using photon interrogation. The system uses a pulsed electron beam from an electron linear accelerator to produce high-energy photon bur sts from a metallic converter. The photons induce fissions in a TRU waste p ackage which is inside an original neutron separating and counting cavity ( NS2C). When fission is induced in trace amounts of TRU contaminants in wast e material, it provides "signatures" from fission products that call be use d to assay the material before disposal. We give here the results from coun ting photofission-induced delayed neutrons from Pu-239, U-235 and U-238 in sample matrices. We counted delayed neutrons emitted after each pulse of th e LINAC by using the sequential photon interrogation and neutron counting s ignatures (SPHINCS) technique which had been developed in the present frame work. The SPHINCS method enhances the available counts by a factor of about 20 compared with the counting of delayed neutrons only, after the irradiat ion period. Furthermore, the use of SPHINCS measurement technique coupled w ith the NS2C facility improves the signal-to-noise ratio by a factor of abo ut 30. This decreases the detection limit. The electron linear accelerator operates at 15 MeV, 140 mA, and 2.5 mu s wide pulse at a 50 and 6.25 Hz rat e. The dynamics of photofission and delayed neutron production, NS2C advant ages and performances, use of an electron linear accelerator as a particle source, experimental and electronics details, and future experimental works are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.