Dismantling and decommissioning: The interest of passive neutron measurement to control and characterise radioactive wastes containing uranium

This paper deals with the evacuation of the wastes resulting from the dismantling of an 235U enrichment facility. Gamma-ray spectrometry is usually used to quantify the 235U residual mass and the activity of those wastes. In the present case, the waste internal content made of aluminium prevents gamma-rays from reaching the detector. We show here how neutron passive measurement has been used as an alternative to gamma-ray spectrometry. The controlled objects are about 1000 compressors of masses up to 2000 kg employed in a gaseous diffusion enrichment process. A dedicated neutron-based setup has been designed using Monte Carlo modelling, and a Detection Limit Mass (DLM) of about 4–6 g of 235U is reached. For one of the compressors, the 235U measured mass has been compared to the same mass determined by destructive methods. The comparison shows a very good agreement.

► Application of passive neutron measurement the SOURCES4C code and the MCNP4C2 Monte Carlo code Detection Limit Mass (DLM) of less than a few grams of 235U one thousand compressors have to be industrially measured.