Comparative assessment of disposal of TRU waste in a greater-confinement disposal facility

This study reviewed previous work that established generic limits for shallow land burial of TRU contaminated wastes and extended previous methodology to estimate approximate appropriate burial limits for TRU wastes in an arid zone greater confinement disposal facility (GCDF). An erosion scenario provided the limiting pathway in the previous determination of generic shallow land burial limits. Erosion removed the cover soil, exposing the waste mass to habitation and agriculture. For the deep burial concept (that is, burial at a depth greater than 10 m (33 ft)), the aquifer transport scenario was controlling. In both cases, the assumed site conditions were characteristic of a humid zone in which groundwater flows immediately below the waste deposit. In deriving limits for an arid site GCDF, either the erosion/reclaimer or the aquifer transport scenario could provide the controlling pathway, depending on the nuclide and the assumed burial depth. The derived limits were higher for the arid sited GCDF than those of the generic humid study. The physical processes that increase limits relative to the generic study include increased time during which radioactive decay occurs prior to release and increased dilution. Some nuclides were effectively unlimited in an arid zone GCDF, while others (notably Pu-239)more » were affected on a much smaller scale, primarily due to very long half-lives. As a final comment, the limit values derived in this report represent adjustments to the calculations of the Healy and Rodgers report (LA-UR-79-100). Those original calculations were very conservative, utilizing a worst case approach, but nevertheless involving significant levels of uncertainty in key assumptions. Consequently, the results are assumption dependent. Other approaches to such an analysis could, and should be used to develop site specific concentration limits for TRU wastes.« less