THE PERFORMANCE ASSESSMENT IMPACTS OF DISPOSAL OF HIGH- MOISTURE, LOW-LEVEL RADIOACTIVE WASTE AT THE NEVADA TEST SITE

A panel of independent scientists was convened by the Department of Energy to assess the performance impacts of disposal of low-level radioactive waste from the Fernald Environmental Management Project. This waste stream was involved in a transportation incident in December 1997. A resulting outgrowth of investigations of the transportation incident was the recognition that the waste was transported and disposed in stress-fractured metal boxes and some of the waste contained excess moisture (high volumetric water contents). The panel was charged with determining whether disposal of this waste in the Area 5 radioactive waste management site on the Nevada Test Site has impacted the conclusions of the completed performance assessment. Three questions were developed by the panel to assess performance impacts: (1) the performance impacts of reduced container integrity, (2) the impact of reduced container integrity on subsidence of waste in the disposal pits and (3) the performance impacts of excess moisture. No performance or subsidence impacts were noted from disposal of the Fernald waste. The impacts of excess moisture were assessed through simulation modeling of the movement of moisture in the vadose zone assuming high water contents (wet waste) for different percentages of the waste inventory. No performance impacts were noted for either the base-case scenario (ambient conditions) or a scenario involving subsidence and flooding of the waste cells. The absence of performance impacts results form the extreme conservatism used in the Area 5-performance assessment and the robust nature of the disposal site.