Publications

This LDRD project has produced a tool that makes probabilistic risk assessments (PRAs) of nuclear reactors - analyses which are very resource intensive - more efficient. PRAs of nuclear reactors are being increasingly relied on by the United States Nuclear Regulatory Commission (U.S.N.R.C.) for licensing decisions for current and advanced reactors. Yet, PRAs are produced much as they were 20 years ago. The work here applied a modern systems analysis technique to the accident progression analysis portion of the PRA; the technique was a system-independent multi-task computer driver routine. Initially, the objective of the work was to fuse the accident progression event tree (APET) portion of a PRA to the dynamic system doctor (DSD) created by Ohio State University. Instead, during the initial efforts, it was found that the DSD could be linked directly to a detailed accident progression phenomenological simulation code - the type on which APET construction and analysis relies, albeit indirectly - and thereby directly create and analyze the APET. The expanded DSD computational architecture and infrastructure that was created during this effort is called ADAPT (Analysis of Dynamic Accident Progression Trees). ADAPT is a system software infrastructure that supports execution and analysis of multiple dynamic event-tree simulations on distributed environments. A simulator abstraction layer was developed, and a generic driver was implemented for executing simulators on a distributed environment. As a demonstration of the use of the methodological tool, ADAPT was applied to quantify the likelihood of competing accident progression pathways occurring for a particular accident scenario in a particular reactor type using MELCOR, an integrated severe accident analysis code developed at Sandia. (ADAPT was intentionally created with flexibility, however, and is not limited to interacting with only one code. With minor coding changes to input files, ADAPT can be linked to other such codes.) The results of this demonstration indicate that the approach can significantly reduce the resources required for Level 2 PRAs. From the phenomenological viewpoint, ADAPT can also treat the associated epistemic and aleatory uncertainties. This methodology can also be used for analyses of other complex systems. Any complex system can be analyzed using ADAPT if the workings of that system can be displayed as an event tree, there is a computer code that simulates how those events could progress, and that simulator code has switches to turn on and off system events, phenomena, etc. Using and applying ADAPT to particular problems is not human independent. While the human resources for the creation and analysis of the accident progression are significantly decreased, knowledgeable analysts are still necessary for a given project to apply ADAPT successfully. This research and development effort has met its original goals and then exceeded them.

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This primer presents a succinct summary of the evolution of U.S. nuclear deterrence policy from the initial development of nuclear weapons until the present day. This is not a definitive history but an introduction to deterrence policy for those with limited background in this area. The concept of deterrence is discussed in several ways--in a general description of deterrence theory, in an historical review of nuclear policy evolution, in a discussion of the future of deterrence, in historical examples of deterrence successes and failures, and in a review of significant contributors to the study of nuclear policy. The intent is to present an authoritative, unclassified account. To accomplish this, to the extent possible, primary source documents were located and utilized if they were available and declassified. These included unclassified Presidential nuclear policy guidance from the Presidential libraries, official JCS histories and State Department Foreign Relations histories. The writings of noted nuclear strategists and historians were also valuable resources for this primer on U.S. strategic nuclear policy.

We technologists generally only address risk magnitudes in our analyses, although other studies have found nineteen additional dimensions for the way the public perceives risk. These include controllability, voluntariness, catastrophic potential, and trust in the institution putting forth the risk. We and the geneml public use two different languages, and to understand what their concerns are, we need to realize that the culture surrounding nuclear weapons is completely alien to the general public. Ultimately, the acceptability of a risk is a values question, not a technical question. For most of the risk dimensions, the public would perceive no significant difference between using oralloy and plutonium. This does not mean that the suggested design change should not be proposed, only that the case for, or against, it be made comprehensively using the best information available today. The world has changed: the ending of the cold war has decreased the benefit of nuclear weapons in the minds of the public and the specter of Chernobyl has increased the perceived risks of processes that use radioactive materials. Our analyses need to incorporate the lessons pertinent to this newer world.

A Level III probabilistic risk assessment (PRA) has been performed for N Reactor, a Department of Energy (DOE) production reactor located on the Hanford reservation in Washington. The objectives of the PRA are to assess the risks to the public and the Hanford site workers posed by the operation of N Reactor, to compare those risks to proposed DOE safety goals, and to identify changes to the plant that could reduce the risk. The scope of the PRA is comprehensive, excluding only sabotage and operation errors of commission. State-of-the-art methodology is employed based largely on the methods developed by Sandia for the US Nuclear Regulatory Commission in support of the NUREG-1150 study of five commercial nuclear power plants. The structure of the probabilistic models allowed complex interactions and dependencies between systems to be explicitly considered. Latin Hypercube sampling techniques were used to develop uncertainty distributions for the risks associated with postulated core damage events initiated by fire, seismic, and internal events as well as the overall combined risk. The combined risk results show that N Reactor meets the primary DOE safety goals and compared favorably to the plants considered in the NUREG-1150 analysis. 36 figs., 81 tabs.