Nathan E. Bixler

Potential for water-table excursions induced by seismic events at Yucca Mountain, Nevada

The possibility that 100-200 m changes in water-table elevation can be mechanically induced by earthquakes is a consideration in site studies of a potential high-level nuclear waste repository at Yucca Mountain, Nevada. However, numerical simulations of tectonohydrologic coupling involving earthquakes typical of the Basin and Range province produce 2-3 m excursions of a water table that is 500 m below the land surface. Even displacements corresponding to extraordinary seismic events drive water-table excursions of less than 20 m. Flow resulting from earthquake-induced pore-pressure fields below the water table tends to be mainly horizontal; vertical flows that cause changes of the level of the water table are secondary. Strongly anisotropic permeability, intended to enhance vertical flow within fault zones, only doubles water-table rise in the models considered. These simulations of water-table rise compare well with observations following large earthquakes in the Basin and Range. The authors` models suggest that exceptional hydrologic and/or tectonic conditions would be required to produce substantially larger water-table rises.

Plume Rise Calculations Using a Control Volume Approach and the Damped Spring Oscillator Analogy

The PUFF code was originally written and designed to calculate the rise of a large detonation or deflagration non-continuous plume (puff) in the atmosphere. It is based on a buoyant spherical control volume approximation. The theory for the model is updated and presented. The model has been observed to result in what are believed to be unrealistic plume elevation oscillations as the plume approaches the terminal elevation. Recognizing a similarity between the equations for a classical damped spring oscillator and the present model, the plume rise model can be analyzed by evaluating equivalent spring constants and damping functions. Such an analysis suggests a buoyant plume in the atmosphere is significantly under-damped, explaining the occurrence of the oscillations in the model. Based on lessons learned from the analogy evaluations and guided by comparisons with early plume rise data, a set of assumptions is proposed to address the excessive oscillations found in the predicted plume near the terminal elevation, and to improve the robustness of the predictions. This is done while retaining the basic context of the present model formulation. The propriety of the present formulation is evaluated. The revised model fits the vast majority of the existing data to +/− 25%, which is considered reasonable given the present model form. Further validation efforts would be advisable, but are impeded by a lack of quality existing datasets.Copyright

Comparison of Average Transport and Dispersion Among a Gaussian Model, a Two-Dimensional Model and a Three-Dimensional Model

The Nuclear Regulatory Commission’s (NRC’s) code for predicting off-site consequences, MACCS2[1] (MELCOR Accident Consequence Code System, Version 2), is used for Level 3 Probabilistic Risk Analysis Consequence analyses, planning for emergencies, and cost-benefit analyses. It uses a simplified model for atmospheric transport and dispersion (ATD), that is, a straight-line Gaussian model. This model has been criticized as being overly simplistic, even for its purpose. The justification for its use has been that only average or expected values of metrics of interest are needed for planning and that a simplified model, by averaging metrics of interest obtained using numerous weather sequences one-by-one, compensates for the loss of structure in the meteorology that occurs away from the point of release. The simple model has been retained because of the desire to have short running times on personal computers covering the entire path through the environment, including the food and water pathway, and covering essentially a lifetime of exposure to a contaminated environment.

SecPop Version 4: Sector Population Land Fraction and Economic Estimation Program: Users? Guide Model Manual and Verification Report.

................................................................................................................. iii TABLE OF CONTENTS .................................................................................................. v LIST OF FIGURES ........................................................................................................ vii LIST OF TABLES .......................................................................................................... ix ABBREVIATIONS AND ACRONYMS ........................................................................... xi

Nuclear risk assessment for the Mars 2020 mission environmental impact statement.

In the summer of 2020, the National Aeronautics and Space Administration (NASA) plans to launch a spacecraft as part of the Mars 2020 mission. One option for the rover on the proposed spacecraft uses a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) to provide continuous electrical and thermal power for the mission. An alternative option being considered is a set of solar panels for electrical power with up to 80 Light-Weight Radioisotope Heater Units (LWRHUs) for local component heating. Both the MMRTG and the LWRHUs use radioactive plutonium dioxide. NASA is preparing an Environmental Impact Statement (EIS) in accordance with the National Environmental Policy Act. The EIS will include information on the risks of mission accidents to the general public and on-site workers at the launch complex. This Nuclear Risk Assessment (NRA) addresses the responses of the MMRTG or LWRHU options to potential accident and abort conditions during the launch opportunity for the Mars 2020 mission and the associated consequences. This information provides the technical basis for the radiological risks of both options for the EIS. SAND2013-10589, January 2014 NRA for Mars 2020

Predicted Liquid Atomization from a Spent Nuclear Fuel Reprocessing Pressurization Event.

Spent nuclear fuel reprocessing may involve some hazardous liquids that may explode under accident conditions. Explosive accidents may result in energetic dispersion of the liquid. The atomized liquid represents a major hazard of this class of event. The magnitude of the aerosol source term is difficult to predict, and historically has been estimated from correlations based on marginally relevant data. A technique employing a coupled finite element structural dynamics and control volume computational fluid dynamics has been demonstrated previously for a similar class of problems. The technique was subsequently evaluated for detonation events. Key to the calculations is the use of a Taylor Analogy Break-up (TAB) based model for predicting the aerodynamic break-up of the liquid drops in the air environment, and a dimensionless parameter for defining the chronology of the mass and momentum coupling. This paper presents results of liquid aerosolization from an explosive event.

Software regression quality assurance for MACCS2 : version 2.5.0.0 through version 2.5.0.9.

The “State-of-the-Art Consequence Analyses (SOARCA) Project: Uncertainty Analysis” has used a newer version of the MELCOR Accident Consequence Code Systems Version 2 (MACCS2) than what was previously used in the “SOARCA Project Volume 1: Peach Bottom Integrated Analysis,” NUREG/CR-7110 Volume 1. A software regression quality assurance program has been implemented for MACCS2. The documentation for the quality assurance from MACCS2 Version 2.5.0.0 through 2.5.0.9 ensures continuity between code versions and provides insight into the changes made within MACCS2.

Methodology for Assessment of Uncertain Input Data for a Level-3 PRA Analysis of a Nuclear Reactor Accident using MACCS2

MACCS2 [1] is a probabilistic accident consequence code that estimates the risks from the operation of nuclear installations, based on the postulated frequencies and severities of potential accidents. The risk estimates provide one of many inputs for judgments on risk acceptability and ways to reduce the excess conservatism in offsite consequence calculations. The uncertainty associated with these risk estimates has an important role in guiding efforts to reduce risks.

Coupled hydrothermal flows of liquid and vapor in welded tuff; Numerical modeling of proposed experiment

Pretest calculations of a proposed small-scale, heatpipe experiment have been made using a finite element, multiphase flow, computer code. The purpose of the experiment is to characterize the response of partially saturated, welded, volcanic tuff to the two-phase countercurrent flow induced by an applied temperature gradient. The experimental measurements will be used to refine the presumed permeability and capillary pressure functions, which are used in the finite element analysis. The calculations presented in this paper, using the presumed material functions, show that saturation profiles and experimental time scales are sensitive to applied temperature gradients and initial liquid saturations. The results have been used to predict appropriate experimental parameter ranges. 7 refs., 11 figs.