PROMETHEE: An Alpha Low Level Waste Assay System Using Passive and Active Neutron Measurement Methods

The development of a passive-active neutron assay system for alpha low level waste characterization at the French Atomic Energy Commission is discussed. Less than 50 Bq[] (about 50 g Pu) per gram of crude waste must be measured in 118-l "European" drums in order to reach the requirements for incinerating wastes. Detection limits of about 0.12 mg of effective ²³⁹Pu in total active neutron counting, and 0.08 mg of effective ²³⁹Pu coincident active neutron counting, may currently be detected (empty cavity, measurement time of 15 min, neutron generator emission of 1.6 × 10⁸ s^-1 [4]). The most limiting parameters in terms of performances are the matrix of the drum - its composition (H, Cl...), its density, and its heterogeneity degree - and the localization and self-shielding properties of the contaminant.