Heterogeneity effects on nondestructive assay measurements of enrichment in UF6 cylinders

Volume: 61, December 2020, pages 2-9,

Authors: Allison T. Greaney¹, Susan K. Smith¹, Ramkumar Venkataraman¹, Jason M. Richards¹, Carlos D. Rael², Martyn T. Swinhoe², Duc T. Vo², Ron D. Jeffcoat³, and Glenn A. Fugate¹

¹_{Oak Ridge National Laboratory,} ²_{Los Alamos National Laboratory,} ³_{Savannah River National Laboratory}

Abstract:

Measurements were per formed using mul t iple mechanically cooled high-purity germanium detectors at six positions around standard industrial 30B cylinders (2.2 metric ton) of UF6 to assess if matrix inhomogeneity is detectable and its impacts on the measured apparent uranium enrichment. Uranium enrichment was calculated with FRAM™. Six of the nine cylinders appeared to be homogeneous as indicated by having similarly accurate apparent measured uranium enrichment, at all positions. However, three cylinders appeared to have localized inhomogeneities. This was manifested as very low apparent enrichments, often <10% of the declared value, on one side of the cylinder. Examination of the spectra suggested both elevated 234Th-234mPa daughter isotopes and reduced 235U were measured at these locations. It is hypothesized that these heterogeneous cylinders may have experienced asymmetric solar heating, which caused volatile UF6 to sublime preferentially away from the warmed side. Care should be taken during uranium enrichment verification when applying methods that include gammarays associated wi th daughter nucl ides to the determination of uranium enrichment for cylinders that are stored in sunlight.

Keywords: enrichment; UF6; HPGe; FRAM; spectrometry

Reference guideline:

Greaney, A.T., Smith, S.K., Venkataraman, R., Richards, J.M., Rael, C.D., Swinhoe, M.T., Vo, D.T., Jeffcoat, R.D., & Fugate, G.A. (2020). Heterogeneity effects on nondestructive assay measurements of enrichment in UF6 cylinders. ESARDA Bulletin - The International Journal of Nuclear Safeguards and Non-proliferation, 61, 2-9. https://doi.org/10.3011/ESARDA.IJNSNP.2020.7