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

Highlights: ► 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. - Abstract: 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.