Monte Carlo simulation of high-level radioactive waste characterization with the associated particle technique

The French Alternative Energies and Atomic Energy Commission (CEA) is conducting an R and D program to improve the characterization of long lived and medium activity radioactive waste packages with nondestructive nuclear measurements. Neutron interrogation with the "Associated Particle Technique" (APT), which brings 3D information about waste materials composition, was studied by numerical simulation with the MCNP computer code [1] and MODAR data analysis software [2]. The design of the system is first presented, especially shields and collimators used to limit the detectors count rate because of the intense gamma emission of the waste. The random background due to the neutron generator was also limited by a specific shield as recommended earlier [3]. Then the paper presents numerical simulations illustrating the ability of APT to characterize specific volumes of interest filled with different materials (iron, water, aluminum, PVC, oil) in different waste packages. Main limitations are also identified, such as neutron scattering in the dense, hydrogenous waste matrices