Elemental Characterization of LL-MA Radioactive Waste Packages With the Associated Particle Technique

The French Alternative Energies and Atomic Energy Commission (CEA) and National Radioactive Waste Management Agency (ANDRA) are conducting an R&D program to improve the characterization of long-lived and medium-activity (LL-MA) radioactive waste packages with analytical methods and with non-destructive nuclear measurements. This paper discusses fast neutron interrogation with the associated particle technique (APT), which provides 3D information about the waste material composition. The characterization of volume elements filled with iron, water, aluminium and PVC in bituminized and fibre concrete LL-MA waste packages has been investigated with MCNP and MODAR data analysis software . APT provides useful information about major elements present in the volumes of interest. However, neutron scattering (especially on hydrogen nuclei) spreads the tagged neutron beam out of the targeted volume towards surrounding materials, reducing spatial selectivity. Simulation shows that targets smaller than 1 L can be characterized up to the half-radius of a 225 L bituminized drum, the matrix of which is very rich in hydrogen. Deeper characterization in concrete is possible but limited by counting statistics due to photon attenuation in this dense matrix and, unless large inspection volumes are considered, by the lack of spatial selectivity of the tagged neutron beam due to neutron scattering.