METHODOLOGY FOR DETERMINATION OF RADIOASSAY PROPERTIES FOR RH-TRU WASTE

The Battelle Columbus Laboratories Decommissioning Project (BCLDP) decontamination and decommissioning activities will generate approximately 25 cubic meters of remote-handled transuranic (RH-TRU) wastes, which are planned for ultimate disposal at the Waste Isolation Pilot Plant (WIPP). For WIPP disposal, the isotopic inventory of the waste must be characterized to demonstrate compliance with applicable limits. The BCLDP has developed a methodology that combines limited assay, knowledge of the processes generating the waste, and a dose/weight-to-curie evaluation to determine the isotopic characterization of the waste. The BCLDP methodology determines the isotopic content for an identified TRU waste stream by a combination of (1) representative waste stream sample analyses, (2) application of Oak Ridge Isotope Generation and Depletion (ORIGEN2) code values for isotopes expected in spent nuclear fuel but not represented by the sample analyses, and (3) assessment of cesium (Cs)-137 content of a payload container based on external radiation field measurements and calculation of TRU isotopic content using a ratio of radionuclides based on known Cs-137 content. The measured isotopic distribution (gamma emitters) of a waste stream is combined with values determined through the conservative application of the ORIGEN2 to account for all isotopes. External dose rates for 1 millicurie of an isotopic mix are modeled for different packaging configurations. Field sort charts permit determining the quantity of radionuclides in each waste package from measured weights and dose rates. The inventory of Cs-137 is determined for each drum based on external radiation field measurement using a high-purity germanium detector. Cs-137 is used as an indicator of TRU content of a drum based on the ratio of radionuclides. The methodology determinations are verified on an approved, periodic basis by gamma and/or alpha spectroscopy. The methodology includes the conservative estimation of measurement errors and assumptions used to determine a total uncertainty that is bounding for the methodology. This methodology is consistent with worker safety principles and is optimal for the BCLDP, a small quantity site with limited waste and resources. In addition, given the small fraction of RHTRU wastes to be disposed of at the WIPP, and its insignificant impact on the long-term performance of the repository, the use of sophisticated assay techniques for RH-TRU waste is neither warranted nor necessary. The BCLDP methodology is a simple system that meets the intent of the governing regulations for the WIPP. BACKGROUND AND PROBLEM STATEMENT The Battelle Columbus Laboratories Decommissioning Project (BCLDP) decontamination and decommissioning activities will generate approximately 25 cubic meters of transuranic (TRU) wastes, which is planned for ultimate disposal at the Waste Isolation Pilot Plant (WIPP). The major fraction of the total waste to be generated by the BCLDP is remote-handled (RH) TRU waste. A small amount of contact-handled (CH) TRU waste also may be generated. The