Publications

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The objectives of this study are to identify and evaluate alternative protective action recommendations (PARs) that could reduce dose to the public during a radiological emergency and to determine whether improvements or changes to the federal guidance would be beneficial. The emergency response strategies considered in this study are the following: (1) standard radial evacuation; (2) shelter-in-place followed by radial evacuation; (3) shelter-in-place followed by lateral evacuation; (4) preferential sheltering followed by radial evacuation; and (5) preferential sheltering followed by lateral evacuation. Radial evacuation is directly away from the plant; lateral evacuation is azimuthally (around the compass) away from the direction of the wind. Shelter-in-place is a protective action strategy in which individuals remain in their residence, place of work, or other facility at the time that a general warning is given. Preferential sheltering involves moving individuals to nearby, large buildings, e.g., high-school gymnasiums or courthouses, that afford greater protection than personal residences. This study shows that there are benefits to sheltering if followed by lateral evacuation. However, if the lateral evacuation strategy cannot be implemented, then early radial evacuation is often preferable. The most appropriate PAR depends on the evacuation time estimate (ETE) and, therefore, it is desirable to reduce the uncertainty associated with the ETE. Nuclear Regulatory Commission (NRC) guidance to commercial power plants currently allows for sheltering and/or evacuation as an emergency response to a serious nuclear accident. Frequently, however, licensees and states default to evacuation strategies and do not consider sheltering. Here we evaluate several alternative strategies to determine if standard radial evacuation is best or if other options could reduce the overall risk to the public. We consider two source terms based on the NUREG-1150 study. These involve a rapid release of radioactive material into the atmosphere and a more gradual release. Two variations in timing have also been investigated, but are not reported here. The evaluation was performed for a generic site, which uses a uniform population distribution and typical Midwest meteorological data (Moline, IL). Additional parameters that are varied in the study are the ETE (4-, 6-, 8-, and 10-hour ETEs are considered) and the duration of sheltering (2-, 4-, and 8-hr sheltering periods are considered). Additional sensitivity studies were performed to investigate nonuniform evacuation speed caused by traffic congestion, the time needed to reach a preferential shelter, and the effect of adverse weather conditions as opposed to favorable weather conditions. Adverse weather conditions are those for which precipitation occurs before the leading edge of the plume exits the 10-mile emergency planning zone (EPZ). Ultimately, emergency response strategies are ranked by their potential to reduce adverse health effects for residents within the EPZ. © 2006 by ASME.

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The Department of Energy has assigned to Sandia National Laboratories the responsibility of producing a Safety Analysis Report (SAR) for the plutonium-dioxide fueled Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) proposed to be used in the Mars Science Laboratory (MSL) mission. The National Aeronautic and Space Administration (NASA) is anticipating a launch in fall of 2009, and the SAR will play a critical role in the launch approval process. As in past safety evaluations of MMRTG missions, a wide range of potential accident conditions differing widely in probability and seventy must be considered, and the resulting risk to the public will be presented in the form of probability distribution functions of health effects in terms of latent cancer fatalities. The basic descriptions of accident cases will be provided by NASA in the MSL SAR Databook for the mission, and on the basis of these descriptions, Sandia will apply a variety of sophisticated computational simulation tools to evaluate the potential release of plutonium dioxide, its transport to human populations, and the consequent health effects. The first step in carrying out this project is to evaluate the existing computational analysis tools (computer codes) for suitability to the analysis and, when appropriate, to identify areas where modifications or improvements are warranted. The overall calculation of health risks can be divided into three levels of analysis. Level A involves detailed simulations of the interactions of the MMRTG or its components with the broad range of insults (e.g., shrapnel, blast waves, fires) posed by the various accident environments. There are a number of candidate codes for this level; they are typically high resolution computational simulation tools that capture details of each type of interaction and that can predict damage and plutonium dioxide release for a range of choices of controlling parameters. Level B utilizes these detailed results to study many thousands of possible event sequences and to build up a statistical representation of the releases for each accident case. A code to carry out this process will have to be developed or adapted from previous MMRTG missions. Finally, Level C translates the release (or ''source term'') information from Level B into public risk by applying models for atmospheric transport and the health consequences of exposure to the released plutonium dioxide. A number of candidate codes for this level of analysis are available. This report surveys the range of available codes and tools for each of these levels and makes recommendations for which choices are best for the MSL mission. It also identities areas where improvements to the codes are needed. In some cases a second tier of codes may be identified to provide supporting or clarifying insight about particular issues. The main focus of the methodology assessment is to identify a suite of computational tools that can produce a high quality SAR that can be successfully reviewed by external bodies (such as the Interagency Nuclear Safety Review Panel) on the schedule established by NASA and DOE.

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VICTORIA 2.0 is a mechanistic computer code designed to analyze fission product behavior within the reactor coolant system (RCS) during a severe nuclear reactor accident. It provides detailed predictions of the release of radioactive and nonradioactive materials from the reactor core and transport and deposition of these materials within the RCS and secondary circuits. These predictions account for the chemical and aerosol processes that affect radionuclide behavior. VICTORIA 2.0 was released in early 1999; a new version VICTORIA 2.1, is now under development. The largest improvements in VICTORIA 2.1 are connected with the thermochemical database, which is being revised and expanded following the recommendations of a peer review. Three risk-significant severe accident sequences have recently been investigated using the VICTORIA 2.0 code. The focus here is on how various chemistry options affect the predictions. Additionally, the VICTORIA predictions are compared with ones made using the MELCOR code. The three sequences are a station blackout in a GE BWR and steam generator tube rupture (SGTR) and pump-seal LOCA sequences in a 3-loop Westinghouse PWR. These sequences cover a range of system pressures, from fully depressurized to full system pressure. The chief results of this study are the fission product fractions that are retained in the core, RCS, secondary, and containment and the fractions that are released into the environment.