- post-closure safety case support emphasizing the use of multiple lines of reasoning and natural analogues
- features, events, and processes identification, screening, and analysis
- pre- and post-closure scenario development, justification, and analysis
- conceptual model development and justification
- system level performance assessments
- uncertainty analyses and probabilistic, Monte-Carlo simulations
- characterization and quantification of uncertainty in model inputs and outputs
- global sensitivity/importance analysis of model results
INTERA works with both implementing organizations and regulators of radioactive waste disposal facilities in developing performance assessments (PAs) and safety cases to ensure that public health and safety and the environment are protected to prescribed limits with an acceptable level of confidence. PAs of waste disposal facilities include a “bottom-up” identification of features, events, and processes (FEPs) that can impact the release of radionuclides from the initial waste form, the migration through engineered and natural barrier systems, and ultimately the transport to the accessible environment. Furthermore, since regulatory requirements are typically probabilistic in nature, uncertainties in the data, conceptual models, and long-term environmental conditions must all be properly factored into a system-level safety assessment. INTERA applies a “top-down” safety function approach for barriers, which compliments the FEP approach in the identification and treatment of credible scenarios of potential future events that might perturb the waste isolation facility (e.g., human intrusion, seismicity, climate change).
INTERA’s experience includes using experimental data to derive appropriate process models, and then linking these models into a comprehensive and efficient PA simulation tool (e.g., GoldSim, Ecolego). We have completed analyses ranging from single-barrier studies (e.g., canisters, waste forms) to total system PAs of all engineered and natural barriers. INTERA also brings experience with all aspects of probabilistic risk assessments, from characterizing and quantifying uncertainty in model inputs and predictions, to identifying the key risk-significant factors within the system performance. Our expertise enables the practical application of PAs, probabilistic modeling, risk assessment, and statistical analysis techniques to build confidence that a disposal facility is safe and protective of human health and the environment. For over 15 years, INTERA personnel led the entire PA organization and activities for the USDOE’s proposed HLW repository at Yucca Mountain. We have also performed PAs for active surface and near-surface facilities being used to dispose of wastes generated as part of environmental restoration activities at nuclear production sites and for commercial LLW disposal facilities.