Development of an advanced performance assessment modeling capability for geologic disposal of nuclear waste : methodology and requirements.

This report describes the planning and initial development of an advanced disposal system PA modeling capability to facilitate the science-based evaluation of disposal system performance for a range of fuel cycle alternatives in a variety of geologic media and generic disposal system concepts. The advanced modeling capability will provide a PA model framework that facilitates PA model development, execution, and evaluation within a formal PA methodology. The PA model framework will provide a formalized structure that enables (a) representation and implementation of a range of generic geologic disposal system options, (b) representation of subsystem processes and couplings at varying levels of complexity in an integrated disposal system model, (c) flexible, modular representation of multi-physics processes, including the use of legacy codes, (d) evaluation of systemand subsystem-level performance, (e) uncertainty and sensitivity analyses to isolate key subsystem processes and components, (f) data and configuration management functions, and (g) implementation in HPC environments. The PA model framework includes two main components: a multi-physics modeling capability and a computational framework capability. These capabilities are implemented through integrated suites of computer codes. The multi-physics codes provide the conceptual and mathematical representations of the relevant FEPs. The computational framework codes provide the supporting functions to facilitate the numerical integration (coupling) and implementation of the multi-physics, computationally efficient code execution, and analysis and configuration management of results. The development of an advanced disposal system PA modeling capability for UFD attempts to balance efforts towards these two components; it must provide an adequate range of multi-physics process models and it mu st facilitate adequate multi-physics couplings across the entire disposal system. And, to the extent possible, the code development