Non-destructive assay and computational model for enrichment verification of UF6 cylinders

Verification of 235U enrichment in uranium hexafluoride (UF6) cylinders is often achieved by destructive (DA) and non-destructive assay (NDA) techniques. These techniques are time consuming and need suitable and similar standard. This is in addition to the loss of nuclear material in the case of destructive analysis.This paper introduces an innovative approach for verifying of 235U enrichment in UF6 cylinder. The approach is based on measuring dose rate (μSv/hμSv/h) due to the emitted gamma rays of 235U at the surface of the cylinder and then calculating the activity of uranium and enrichment percentage inside the cylinder by a developed three dimensional model. Attenuation of the main 235U gamma transitions due to the cylinder wall (5B type of Ni alloy) was also calculated and corrected for. The method was applied on UF6 cylinders enriched with 19.75% of 235U. The calculated enrichment was found to be 18% with 9% uncertainty. By the suggested method, the calculated total uranium activity inside one of the investigated UF6 cylinder was found close to the target (certified) value (5.6 GBq) with 9% uncertainty. The method is currently developed by taking into consideration other parameters.