Year
1986
Abstract
In a purification process at the Savannah River Plant (SRP), a long-term gain trend existed in the accountability of enriched uranium. Input accountability assays were suspect, because output assays were made on pure uranium product by the reliable Davies-Gray titration. A major effort was made to improve uranium assays for input accountability. The isotope dilution—mass spectrometry method in use was converted from a volumetric basis to a gravimetric basis. Analysts were formally qualified for performing routine measurements by successfully completing tests on blind standards. Tight quality-control limits were established. The performance of analysts was closely monitored, and it became necessary to limit measurements to several analysts in order to achieve a sustained high level of performance. Quality control standards were monitored and improvements made to ensure valid standards. Standard and sample analytical results were examined for trends on a continuing basis. As improvements in uranium assays continued, it became evident that sampling was a major problem. Existing density validation limits were too broad to be of value. Tight density limits were agreed upon and enforced. With the implementation of a good sample validation program, improvements in uranium assays, and improvements in quality control, the uranium gain trend was eliminated.