Nondestructive Assay of TRU Waste Sludge at Los Alamos National Laboratory

Nondestructive assay (NDA) measurements of Transuranic (TRU) sludge waste at Los Alamos National Laboratory (LANL) shares many of the same measurement complexities that have been encountered at other DOE sites. The sludge matrix is highly attenuating to both gamma rays and neutrons, the homogeneity of matrix and source material inside the drums cannot be verified for every drum, there are no representative standards for sludges, and independent tests intended to ascertain the accuracy of the measurements are not characteristic of the waste form. At LANL, a single instrument has been used to explore the appropriateness of both passive neutron and quantitative gamma ray methods for measuring sludge drums. The passive neutron approach uses the Reals coincidence count rate to establish plutonium mass and other parameters of interest for TRU waste. The quantitative gamma ray method assumes a homogeneous distribution of matrix and source material and assays the drum with a calibration based on the known density of the matrix. Both methods are supplemented by a simultaneous isotopic measurement using Multi-Group Analysis (MGA) to determine the plutonium isotopic composition. This report will discuss the two methods in detail. Included in the discussion will be descriptions of the setup parameters and calibration techniques for the instrument. Then an evaluation of the measurement results, including a summary of the checks and tests that are applied to sludges, will be presented. Finally, a brief discussion of the conclusions that can be drawn from the tests will be offered. (authors)