Variance Propagation at the Portsmouth Uranium Enrichment Plant

The uranium enrichment plant presents unique problems in variance propagation. Some of the commonly discussed sources of measurement uncertainty, such as scale calibration or analytical standardization, are of secondary importance, while a variety of effects often classed as \"nonmeasurement\" sources of uncertainty or \"process variation\" dominate the variance propagation equation. Examples include attempts to define a smooth cascade gradient based on a limited number of point measurements, variations of uranium actually fed to the cascade from the arbitrarilydefined constant value of 0.711% 235U, and physical changes in the cascade during the several hours required to record all needed measurement data. In 1991 Martin-Marietta Energy Systems contracted with 21st Century Industries to implement INDEP, a variance propagation package developed by Ralph Lumb Associates. An initial implementation based on best available data has been completed; current efforts are directed at improving both measurement procedures and the measurement control program to address problems identified by INDEP.