An Execution Strategy Analysis (ESA) capability and tool is being developed to evaluate alternative execution strategies for future deployment of a consolidated Interim Storage Facility (ISF) using a consent-based siting process per the Administration’s Strategy for the Management and Disposal of Used Nuclear Fuel and High-Level Radioactive Waste (Strategy). Application of an ESA approach not only leverages on but also goes beyond traditional project analysis tools. The ESA tool allows for on-going performance assessment of the evolving project execution plan that takes into account significant assumptions, risks, and uncertainties throughout the project lifecycle. The ESA process and tool are used to support the development of plans, budgets, and alternative execution/ implementation strategies for meeting the goals in the Strategy. The paper describes the process by which the ESA capability and tool are continuing to be developed and addresses the value of applying such a process in implementing a long-term strategy for managing used nuclear fuel (UNF) and High Level Radioactive Waste (HLW).

The PRISM (Prioritization Risk Integration Simulation Model), a computer model was developed to support the Department of Energy’s Office of Environmental Management (DOE-EM) in its mission to clean up the environmental legacy from the Nation’s nuclear weapons materials production complex. PRISM provides a comprehensive, fully integrated planning tool that can tie together DOE-EM’s projects. It is designed to help DOE managers develop sound, risk-informed business practices and defend program decisions. It provides a better ability to understand and manage programmatic risks. The underlying concept for PRISM is that DOE-EM “owns” a portfolio of environmental legacy obligations (ELOs), and that its mission is to transform the ELOs from their current conditions to acceptable conditions, in the most effective way possible. There are many types of ELOs - contaminated soils and groundwater plumes, disused facilities awaiting D&D, and various types of wastes waiting for processing or disposal. For a given suite of planned activities, PRISM simulates the outcomes as they play out over time, allowing for all key identified uncertainties and risk factors. Each contaminated building, land area and waste stream is tracked from cradle to grave, and all of the linkages affecting different waste streams are captured. The progression of the activities is fully dynamic, reflecting DOE-EM’s prioritization approaches, precedence requirements, available funding, and the consequences of risks and uncertainties. The top level of PRISM is the end-user interface that allows rapid evaluation of alternative scenarios and viewing the results in a variety of useful ways. PRISM is a fully probabilistic model, allowing the user to specify uncertainties in input data (such as the magnitude of an existing groundwater plume, or the total cost to complete a planned activity) as well as specific risk events that might occur. PRISM is based on the GoldSim software that is widely used for risk and performance assessment calculations. PRISM can be run in a deterministic mode, which quickly provides an estimate of the most likely results of a given plan. Alternatively, the model can be run probabilistically in a Monte Carlo mode, exploring the risks and uncertainties in the system and producing probability distributions for the different performance measures. BACKGROUND Over the past decade the Office of Environmental Management (EM) has been criticized for the lack of a formal risk-based decision tool for use at Headquarters to properly prioritize projects and funding throughout the EM complex. In 2002, the DOE Top-to-Bottom Review Team [1] recommended that DOE take steps to move toward a risk-based cleanup approach. The National Research Council in 2005 [2] recommended DOE revamp the way DOE goes about implementing risk-informed approaches applied to waste disposition decisions.

The Used Fuel Disposition (UFD) Campaign within DOE-NE is evaluating storage and disposal options for a range of waste forms and a range of geologic environments. For each waste form and geologic environment combination, there are multiple options for repository conceptual design. The Disposal Systems Evaluation Framework (DSEF) is being developed to formalize the development and documentation of options for each waste form and environment combination. The DSEF is being implemented in two parts. One part is an Excel workbook with multiple sheets. This workbook is designed to be user friendly, such that anyone within the UFD Campaign can use it as a guide to develop and document repository conceptual designs that respect thermal, geometric, and other constraints. The other part is an Access relational database file that will be centrally maintained to document the ensemble of conceptual designs developed with individual implementations of the Excel workbook. The DSEF Excel workbook includes sheets for waste form, environment, geometric constraints, engineered barrier system (EBS) design, thermal, performance assessment (PA), materials, cost, and fuel cycle system impacts. Each of these sheets guides the user through the process of developing internally consistent design options, and documenting the thought process. The sheets interact with each other to transfer information and identify inconsistencies to the user. In some cases, the sheets are stand-alone, and in other cases (such as PA), the sheets refer the user to another tool, with the user being responsible to transfer summary results into the DSEF sheet. Finally, the DSEF includes three top-level sheets: inputs & results, interface parameters, and knowledge management (references). These sheets enable users and reviewers to see the overall picture on only a few summary sheets, while developing the design option systematically using the detailed sheets. The DSEF Access relational database file collects the key inputs, results, and interface parameters from each Excel workbook implementation. The power of a relational database is available to sort and organize groups of designs, and to answer queries about what evaluations have been done in the UFD Campaign.