Optimisation and uncertainty estimation of the enrichment meter measurement technique for UF6 cylinders

Volume: 59, December 2019, pages 2-10,

Authors: Jean-Luc Dufour, Nicolas Pepin, Clement Deyglun and Anne-Laure Weber

_{Institut de Radioprotection et de Sûreté Nucléaire (IRSN)}

Abstract:IRSN carries out on-site non-destructive assay of nuclear material for domestic safeguards purposes in France. The paper presents the study of uncertainty components and the optimisation of the traditional uranium enrichment meter method, applied to UF6 in 30B and 48Y cylinders. This calibration-based gamma spectrometry technique measures the enrichment by quantifying the count rate in the 185.7 keV peak of uranium 235 in conditions of infinite thickness of the measured material. It is based on high resolution gamma spectrometry measurements coupled with an ultrasonic gauge. The calibration is performed with the spectrometer in a collimated geometry using U3O8 laboratory standards, whereas UF6 assays performed onsite are un-collimated in order to reduce the inspection time. Therefore, corrections need to be done to correct for the dif ferences between laboratory and on-site measurements, and associated uncertainties have to be taken into account. A measurement of the container wall thickness is performed using an ultrasonic gauge in order to correct the gamma ray attenuation through the container wall. On-site tests and MCNP simulations were also performed to calculate a calibration transfer factor and evaluate the impact of different detector localisations on the count-rate acquisition. In addition, these tests showed the impact of the background, mainly due to the higher energy gamma rays of U-238 daughters that Compton scattered within UF6 and the detector. Finally, the measurement time was estimated, the use range of the technique was defined and the measured uranium enrichment uncertainty was calculated.

Keywords: enrichment; UF6; spectrometry; uncertainty; MCNP.

Reference guideline:

Dufour, J-L., Pepin, N., Deyglun, C., & Weber, A-L. (2019). Optimisation and uncertainty estimation of the enrichment meter measurement technique for UF6 cylinders. ESARDA Bulletin - The International Journal of Nuclear Safeguards and Non-proliferation, 59, 2-10. https://doi.org/10.3011/ESARDA.IJNSNP.2019.9