Year
1982
Abstract
A nondestructive-assay (NDA) measurements program used to verify the 235U content of fast-breederreactor fuel elements before and after cladding modifications is described. NDA measurements were carried out over an approximate one-year period with excellent results. The measurements program was based on a quantitative assay of a random sample of elements issued for modification and of a second random sample of fuel returned to storage. The use of \"attribute sampling\" greatly reduced the measurement effort required, while providing a rigorous basis for stating that less than a goal quantity of 0.35 kg of enriched uranium (out of a total of 124 kg) could be lost without detection. Element assay was carried out using gamma-scanning techniques; the 186-keV 235U gamma-ray line was measured (with background subtraction) over the full length of each sampled element. The assay results were then compared with a two-parameter calibration equation computed from a least-squares fit to standard fuel-element data. Data for \"before\" and \"after\" batches of elements were accumulated as they were issued and returned. It was successfully shown that no detectable losses occurred during the modification program.