Year
2016
Abstract
Because Oak Ridge National Laboratory (ORNL) is a research facility, its transuranic wastes are more complex and varied than those from weapons-production sites. To date, thirteen distinct transuranic waste streams have been identified at ORNL. Some of these wastes originate from carefully-controlled processes, while others are by-products of analytical and process development. Plutonium is present in some, but by no means all, of the waste streams. Before a waste container can be transported to a waste repository, it is necessary to characterize its radionuclide content, especially its activity, fissile content, decay heat, and transuranic concentration. Nondestructive assay (NDA) is routinely applied to characterize each waste container. For those wastes containing plutonium, it is helpful to know the weight fractions of the various Pu isotopes. The minor isotopes can then be computed in ratio to a major (or fiducial) isotope. Gamma ray isotopic measurements provide the best NDA estimate of the Pu weight fractions, but if the plutonium concentration is low or if the waste contains a lot of Cs-137, isotopic measurement may not be possible. Wastes from carefully-controlled processes may be consistent enough to permit application of a set of declared isotopic fractions where measured isotopics are unavailable. In such cases, the minor Pu isotopes are derived using declared isotopics as default values. This paper presents measurement results from several Pu-bearing waste streams, and compares them to the anticipated values from corresponding declared isotopic fractions. The paper also discusses occasions when measurement results differ from acceptable knowledge (AK) of a process, and the consequences if AK information is found to be incorrect.