Abstract:The Waste Isolation Pilot Plant (WIPP) is a US Department of Energy (DOE) facility for the permanent disposal of defense-related transuranic (TRU) waste. US Environmental Protection Agency (EPA) regulations specify that the DOE must demonstrate on a sound basis that the WIPP disposal system will effectively contain long-lived alpha-emitting radionuclides within its boundaries for 10,000 years following closure. In 1996, the DOE submitted the 40 CFR The 1996 WIPP PA model of the disposal system included conceptual and mathematical representations of key hydrologic and geochemical processes. These key processes were identified over a 22-year period involving data collection, data interpretation, computer models, and sensitivity studies to evaluate the importance of uncertainty and of processes that were difficult to evaluate by other means. Key developments in the area of geochemistry were the evaluation of gas generation mechanisms in the reposito~,
For submittal to Reliability Engineering and System SafetyThe WIPP is a DOE facility for the permanent disposal of defense-related TRU waste.The facility is located about 42 km east of the town of Carlsbad in southeastern NewMexico ( properties of the Salado, primarily its geologic stability and its isolation capability.lg However, regulations specifi that performance of the WIPP shall be predicted based on extrapolating current land-use practices in the vicinity of WIPP to 10,000 years. 18'6Furthermore, although administrative controls will be implemented and passive markers will be built to deter incompatible activities, the EPA regulations require the assumption that controls and markers are ineffective beyond 100 years after closure.18>Becausepotash and hydrocarbon resources occur in the WD?P vicinity and are currently being developed and extracted, predictions of WIPP performance must include the potential effects of such development inside the disposal system. These considerations lead to the disturbed-performance (or human-intrusion) scenario as the dominant factor in evaluating compliance with the EPA regulations (Figure 3). In the 1996 WIPP PA, the disturbed- Conceptual models describe with words and diagrams the processes that occur within the disposal system (or have a reasonable likelihood of occurring). It is recognized that conceptual models can be formulated at varying levels of complexity and realism, and this has occurred on the WIPP Project. In many cases, the conceptual models developed to explain detailed observations are much more complicated than the conceptual models explicitly represented in the 1996 WIPP PA. The requirements of the system-level PA Larson, Development of the Conceptual Models...,