Wall Correction in Enrichment Measurements based on the Enrichment Meter Principle

摘要

The Enrichment Meter Principle (EMP) is the physical justification of a commonly used technique to determine the ~(235)U-to-~(tot)U atom fraction (enrichment) of bulk uranium compounds in situ. It is applied across the nuclear fuel cycle subject to the condition that the material is known to be of a single enrichment. It states that for a given compound, and fixed collimated gamma spectrometer, with its fixed field of view directed at an item such that there is effectively infinite path length (in terms of mean free paths) within the compound in all directions, the atom fraction (enrichment) is directly proportional to the net full energy peak counting rate of the 185.7 keV gamma-line produced directly from the decay of ~(235)U. One familiar application of the EMP is the determination of enrichment of UF_6 in storage cylinders. In practice the difference in the thickness of the container walls from the condition used to calibrate the instrument must be corrected for. Mortreau and Berndt describe an approach and model to estimating the wall correction factor based on numerical integration over the distribution of contributory rays. In this paper we review this approach and derive wall attenuation correction for case studies involving the measurement of UF_6 cylinders using LaBr_3 scintillation detectors and applying EMP. Several matters are raised involving the need to clarify and standardize wall correction terminology and strategy.