Performance Assessment Projects
Yucca Mountain Project
Since 1991, INTERA has provided performance assessment and scientific modeling to help determine the suitability of the proposed site for a high level radioactive waste repository at Yucca Mountain. The evaluation of the ability of the overall waste disposal system (including geosphere) to meet the objectives specified in applicable regulatory standards has been termed total system performance assessment (TSPA). INTERA has participated in several TSPAs in support of the Viability Assessment and Site Recommendation studies as well as the ongoing License Application phase of the project. These comprehensive, integrated, risk-based evaluations of the performance of the potential site are based on site characterization data, process level modeling, and expert elicitation. The TSPA model synthesizes information from detailed infiltration modeling in the vadose zone, thermal hydrologic modeling, waste package degradation modeling, waste form alteration, flow and transport of radionuclides (fracture and matrix) in the unsaturated and saturated zones, and biosphere uptake modeling. TSPA calculations are performed with the GoldSim code, which integrates all related process models and uses a Monte-Carlo methodology to create multiple random combinations of uncertain variables to compute the probabilistic performance of the entire waste-disposal system in terms of dose to the receptor.
We have also completed a comparative study of uncertainty importance ranking techniques for interpreting probabilistic performance assessment results. Based on these findings, multivariate statistical techniques (e.g., non-parametric regression modeling and classification tree analysis) are applied to Monte Carlo simulation results to determine key drivers of uncertainty in projections of performance for the potential nuclear waste repository. In support of the TSPA modeling studies, INTERA personnel have developed the object-oriented Geoscience Model Visualization software called mView. mView allows the user to prepare two-dimensional (2D) and three-dimensional (3D) graphical representations of numeric model geometry and output results from different process models. Existing interfaces for mView accept simulation data from different codes including TOUGH2, NUFT, FRAC3DVS, FEHMN, and SWIFT.
Effects of Repository Vault Geometry
INTERA conducted a scenario modeling and sensitivity analysis program for the Nuclear Waste Management section of Ontario Power Generation. The FRAC3DVS code was used to create detailed three dimensional flow models for two different disposal scenarios (in room and in floor). Contaminant transport was modeled for release scenarios of Iodine 129 and Technetium 99. Sensitivity assessments of model results to hydrogeologic conditions and emplacement materials were also conducted. The mView pre-and post-processing system, developed by INTERA personnel, was used for all grid generation, property assignment and result visualization.
Preliminary Performance Assessment
INTERA, under contract to ANDRA, developed a preliminary performance assessment model for the proposed HLW repository at the Este site in eastern France. To accomplish this, we developed and implemented a transport modeling scenario with the GoldSim code. The modeling results were compared to a standard transport model for verification. In a second step, the GoldSim model was used for sensitivity analysis to identify the critical parameters that affect the transport of radionuclides from a potential repository. For the sensitivity analysis, the probabilistic results were analyzed using the statistical software program SATOOL, developed by INTERA.
Virtual Engineering System
INTERA supported the development of a virtual engineering system for high level radioactive waste disposal in Japan being conducted for the Power Reactor and Nuclear Fuels Development Corporation (PNC) of Japan. This multi year project produced the initial framework for a computer-integrated engineering assessment environment, termed the Virtual Engineering System for Geological Isolation (VES-GI). Using sophisticated computer science technology, VES-GI was intended to provide three basic capabilities: virtual construction of alternative geologic isolation system designs to support scenario analysis and screening; simulation of virtual system behavior to compare various expected scenarios; and virtual reality based visualization to demonstrate disposal system behavior and safety to the general public and to promote public acceptance. The state of the art visualization technologies will also enhance scenario analysis and performance assessment (PA) by technical personnel.
INTERA personnel worked in three primary areas of responsibility for the VES GI project including the development of performance assessment methodology, scientific visualization and software engineering, and decision analysis and probabilistic risk assessments. In the area of performance assessment, we identified generic technical requirements for a Japanese conceptual repository consisting of an engineered barrier system and a natural barrier system. We then developed a performance assessment framework for VES GI in which the behavior of the system under a selected scenario can be examined, and in which alternative (“what if”) scenarios can be compared. Applying a performance assessment framework gives VES GI the flexibility to be used for scenario analyses, evaluations of system simulations, performance assessment model development and calculations, and public acceptance evaluations. The performance assessment framework provides the strong, defensible scientific basis necessary for all these system analyses.
