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Heterogeneity effects on nondestructive assay measurements of enrichment in UF6 cylinders

Journal Article · · ESARDA Bulletin
OSTI ID:1756280
 [1];  [1];  [1];  [1];  [1];  [2];  [2];  [3]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
+ Show Author Affiliations
A set of measurements were performed using multiple mechanically cooled HPGe detectors at six positions around a cylinder uranium hexafluoride to assess if matrix inhomogeneity is detectible and effects the determined apparent uranium enrichment. These measurements were performed on nine 30B cylinders of uranium hexafluoride. Six of the cylinders appeared to be homogeneous and had similar apparent measured uranium enrichment, as calculated by the FRAM software, at all positions. However, three cylinders appeared to have local inhomogeneity based on the observed results. This was manifested as very low apparent enrichments, often <10% of the declared enrichment, on select positions. The side with a low apparent enrichment shows elevated daughter isotope activity (e.g., elevated 1001 keV and 766 keV peak count rate) and slightly reduced 235U activity (lower 185.7 keV count rate). We hypothesize that these heterogenous cylinders may have experienced asymmetric solar heating, which caused volatile UF6 to sublime preferentially away from the warmed side. A similar phenomenon was observed at a second facility where dose rate measurements confirm that the “low-enriched side” of cylinders show elevated gamma ray dose rates, likely from the removal of UF6 attenuation and concentration of daughter-products. Care should be taken during uranium enrichment verification when applying methods that include gamma-rays associated with daughter nuclides to the determination of uranium enrichment on cylinders that are stored in sunlight and have asymmetric dose readings around the cylinder.
Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1756280
Journal Information:
ESARDA Bulletin, Journal Name: ESARDA Bulletin Journal Issue: 1 Vol. 61; ISSN 0392-3029; ISSN 1977-5296
Publisher:
European Safeguards Research & Development AssociationCopyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
enrichment
FRAM
HPGe
spectrometry
UF6