Wall Correction In Enrichment Measurements Based On The Enrichment Meter Principle

The enrichment meter principle is the physical justification of a commonly used technique to determine the 235 U-to- tot U atom fraction (enrichment) of bulk uranium compounds <i>in situ</i>. This concept is applied across the nuclear fuel cycle subject to the condition that the material is known to be of a single enrichment. The principle 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 <i>directly</i> 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 enrichment meter principle is the determination of enrichment of UF₆ in storage cylinders. In practice, a correction must be applied to account for the difference in the thickness of the container walls from the condition used to calibrate the instrument. In 2017, Mortreau and Berndt described 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 compare predictions of a general-purpose commercially available ray tracing code to experimental data. This presentation will discuss several matters involving the need to clarify and standardize wall correction terminology and strategy.