WASTE ASSAY AND MASS BALANCE FOR THE DECONTAMINATION AND VOLUME REDUCTION SYSTEM AT LANL

The Decontamination and Volume Reduction System (DVRS) operated by the Solid Waste Operations (SWO) Group at Los Alamos National Laboratory (LANL) processes large volume, legacy radioactive waste items. Waste boxes, in sizes varying from 4 ft x 4 ft x 8 ft to 10 ft x 12 ft x 40 ft, are assayed prior to entry into the processing building. Inside the building, the waste items are removed from their container, decontaminated and/or size reduced if necessary, and repackaged for shipment to the Waste Isolation Pilot Plant (WIPP) or on-site low-level waste disposal. The repackaged items and any secondary waste produced (e.g., personal protective equipment) are assayed again at the end of the process and a mass balance is done to determine whether there is any significant hold-up material left in the DVRS building. The DVRS building is currently classed as a radiological facility, with a building limit of 0.52 Ci of Pu239 and Am241, and 0.62 Ci of Pu238, the most common radionuclides processed. This requires tight controls on the flow of nuclear material. The large volume of the initial waste packages, the (relatively) small amounts of radioactive material in them, and the tight ceiling on the building inventory require accurate field measurements of the nuclear material. This paper describes the radioactive waste measurement techniques, the computer modeling used to determine the amount of nuclear material present in a waste package, the building inventory database, and the DVRS process itself. Future plans include raising the limit on the nuclear material inventory allowed in the building to accommodate higher activity waste packages. All DOE sites performing decontamination and decommissioning of radioactive process equipment face challenges related to waste assay and inventory issues. This paper describes an ongoing operation, incorporating lessons learned over the life of the project to date.