Alpha-Particle Low-Level Waste Control: Improvement of the PROMETHEE 6 Assay System Performances

The PROMpt, Epithermal and THErmal interrogation Experiment, version 6 (1996) (PROMETHEE 6) assay system for alpha-particle low-level waste characterization, developed for research and development purposes, includes both passive and active neutron measurement methods. Developed at the Commissariat à l'Energie Atomique, Cadarache Centre, in cooperation with COGEMA, its aim is to reach the incinerating alpha-particle waste requirements (<50 Bq[]/g of crude waste, i.e., ~50 g of Pu per drum) in 118-l "European" drums (460 mm in diameter and 750 mm high). Good preliminary results were presented: detection limits of ~0.12 mg of effective ²³⁹Pu in total active neutron counting and 0.08 mg of effective ²³⁹Pu in coincident active neutron counting [empty cavity, measurement time of 15 min, neutron generator emission of 1.6 × 10⁸ s^-1 (4)]. Those results are improved with the use of a higher neutron source emission [GENIE 36 generator, neutron emission of 2.4 × 10⁹ s^-1 (4)] and working on the configuration of the detector units. In the total counting mode, the gain is a factor of ~4 in a cellulose matrix and 3.1 in a polyvinyl chloride matrix. In the coincidence counting mode, these factors are 1.8 and 1.7, respectively. After a very short description of PROMETHEE 6, this paper presents the last and best performances that were obtained with the increased neutron source. Studies on the detection limit variations with the use of borated shields in front of the detection units and around the neutron generator also are dealt with.