Paul H. Gudiksen

Chernobyl source term, atmospheric dispersion, and dose estimation

The Chernobyl source term available for long-range transport was estimated by integration of radiological measurements with atmospheric dispersion modeling and by reactor core radionuclide inventory estimation in conjunction with WASH-1400 release fractions associated with specific chemical groups. These analyses indicated that essentially all of the noble gases, 60% of the radioiodines, 40% of the radiocesium, 10% of the tellurium, and about 1% or less of the more refractory elements were released. Atmospheric dispersion modeling of the radioactive cloud over the Northern Hemisphere revealed that the cloud became segmented during the first day, with the lower section heading toward Scandinavia and the upper part heading in a southeasterly direction with subsequent transport across Asia to Japan, the North Pacific, and the west coast of North America. The inhalation doses due to direct cloud exposure were estimated to exceed 10 mGy near the Chernobyl area, to range between 0.1 and 0.001 mGy within most of Europe, and to be generally less than 0.00001 mGy within the United States. The Chernobyl source term was several orders of magnitude greater than those associated with the Windscale and TMI reactor accidents. However, the 137Cs from the Chernobyl event is about 6% of that released by the U.S. and U.S.S.R. atmospheric nuclear weapon tests, while the 131I and 90Sr released by the Chernobyl accident was only about 0.1% of that released by the weapon tests.

Experimental Design of the 1984 ASCOT Field Study

Abstract During September and October of 1984 the Department of Energys Atmospheric Studies in Complex Terrain program conducted an intensive field study in the Brush Creek Valley of western Colorado. The overall objective of the study was to enhance the understanding of pollutant transport and diffusion associated with valley flows. Data collections were designed to investigate nocturnal and morning transition wind, turbulence, and temperature fields in the valley, in its tributaries, and on its side-slopes, and how these are affected by the free stream conditions above the valley. The release and sampling of atmospheric tracers were used to study transport and diffusion. The experimental design of this study is presented.

Dose Estimates from the Chernobyl Accident

The Lawrence Livermore National Laboratory Atmospheric Release Advisory Capability (ARAC) responded to the Chernobyl nuclear reactor accident in the Soviet Union by utilizing long-range atmospheric dispersion modeling to estimate the amount of radioactivity released (source term) and the radiation dose distribution due to exposure to the radioactive cloud over Europe and the northern hemisphere. In later assessments, after the release of data on the accident by the Soviet Union, the ARAC team used their mesoscale-to-regional-scale model to focus on the radiation dose distribution within the Soviet Union and the vicinity of the Chernobyl plant.

The Dispersion of Atmospheric Tracers in Nocturnal Drainage Flows

Abstract This paper summarizes the results of a series of perfluorocarbon tracer experiments that were carried out in the Brush Creek Valley in western Colorado under the auspices of the Atmospheric Studies in Complex Terrain (ASCOT) program. The results indicate that tracers entrained within the valleys nocturnal drainage flows displayed well defined plumes that were not influenced significantly by the larger scale flows above this deep and narrow valley. Thus, the spatial distributions of the tracers were primarily governed by the structure of the drainage flows. None of the tracers released within the valley were detected in significant quantities on the adjoining mesas or within the adjacent valleys prior to sunrise. The process of ventilating the tracers out of the valley was initiated shortly after sunrise by the upslope flows generated along the valley sidewall exposed to the morning sun. The rate of ventilation was influenced by the solar intensity, the ambient meteorology, and the location of th...

Field studies of transport and dispersion of atmospheric tracers in nocturnal drainage flows

Abstract A series of tracer experiments were carried out as part of the Atmospheric Studies in Complex Terrain (ASCOT) program to evaluate pollutant transport and dispersion characteristics of nocturnal drainage flows within a valley in northern California. The results indicate that the degree of interaction of the drainage flows with the larger scale regional flows are strongly dependent on how well the shallow drainage flows are shielded by the surrounding topography from the external environment. For the valley under study, the drainage flows from about mid-slope elevations and below were generally decoupled from the externally generated flows; as evidenced by the similarity of the surface tracer distributions produced during widely varying regional flow conditions. However, tracers released immediately above the drainage flows near the ridge top did reveal considerable mixing between the transition layer flows and the underlying surface drainage flows. Likewise, the transport and dispersion of the tracers at elevated heights within the valley basin were extremely dependent on the influences of the regional scale flows on the valley circulations. The dispersion rates associated with the transition layer flows were dependent on topographic constraints but were appreciably higher than those reported for homogeneous flat terrain situations.

The Dependence of Canyon Winds on Surface Cooling and External Forcing in Colorado's Front Range

Abstract The atmospheric katabatic flow in the foothills of the Front Range of the Rocky Mountains has been monitored by a network of towers and sodars for several years as part of the ASCOT program. The dependence of the outflow from Coal Creek Canyon on surface cooling and channeling by winds above the canyon is explored by using three years of data from a portion of the network. The depth of the drainage flow and the height of the wind speed maximum were found to be largest at external wind speeds near 3 m s−1. For lighter winds aloft, the drainage depth, the height of the jet, and the drainage wind speed depend both on external wind speed and on the strength of the surface cooling. The magnitude of the near-surface temperature differences was also found to decrease with increasing surface cooling, possibly because of increasing turbulence caused by winds interacting with surface topography.

Tributary, Valley and Sidewall Air Flow Interactions in a Deep Valley

Abstract Field experiments measuring nocturnal tributary flows have shown complex internal structure. Variations in the flow range from short-term (8–16 min) oscillations (related to tributary/valley flow interactions) to long-term flow changes throughout the night (related to upper ridge slope and tributary sidewall cooling rate changes). The mean vertical structure in the tributary flow shows a three layer structure. Outflow winds are observed near the surface and in an elevated jet up to several hundred meters height. A flow minimum or counterflow exists at about the height of the drainage flow maximum in the main valley. Comparisons of flow volumes and variations from a single large tributary show that 5%–15% of the nocturnal flow in the main valley may be contributed through one tributary. This implies that tributaries may dominate main valley sidewall and midvalley subsidence contributions to valley drainage flows.

Categorization of nocturnal drainage flows within the Brush Creek Valley and the variability of sigma theta in complex terrain

Abstract The monthly frequencies of nocturnal drainage flows in the Brush Creek Valley were estimated over the period August 1982–January 1985 for the purpose of evaluating the representativeness of the drainage flows observed during a few intensive study periods. These estimates were made on the basis of data from three short meteorological towers situated in the valley. The highest frequencies were observed during the July to October timeframes: 30%–40% during 1983 and 5%–25% during 1984. Of the ten experimental nights when intensive investigations were conducted within the Brush Creek Valley, seven were during strong drainage flow periods and three were during weaker drainage flow periods. The variability of a σθ in complex terrain areas was investigated since this parameter is often used to estimate diffusion of pollutants. Measurements made during strong drainage flow periods within two valleys in The Geysers geothermal area in northern California and within the Brush Creek Valley yielded median hour...

Potential air quality impacts of large-scale geothermal energy development in the Imperial Valley

This report is an assessment of the potential impact on air quality of large-scale (3000 MW) geothermal development in Californias Imperial Valley. The assessment is based on the predictions of numerical atmospheric transport models. Emission rates derived from analyses of the composition of geothermal fluids in the region and meteorological data taken at six locations in the valley over a 1-y period were used as input to the models. Hydrogen sulfide is the emission of major concern. Our calculations predict that at the 3000-MW level (with no abatement), the California 1-h standard for H2S (42 μg m−3) would be violated at least 1% of the time over an area of approximately 1500 km2 (about 13 of the valley area). The calculations indicate that an H2S emission rate below 0.8 g s−1 per 100-MW unit is needed to avoid violations of the standard beyond a distance of 1 km from the source. Emissions of ammonia, carbon dioxide, mercury, and radon are not expected to produce significant ground level concentrations, nor is the atmospheric conversion of hydrogen sulfide to sulfur dioxide expected to result in significant SO2 levels.

Experimental and Model Transport and Diffusion Studies in Complex Terrain with Emphasis on Tracer Studies

The U.S. Department of Energy (DOE) Atmospheric Studies in Complex Terrain (ASCOT) program began in the fall of 1978 as a multiple DOE and other Federal Laboratory program devoted to developing a better physical understanding of atmospheric boundary layer flows in areas of complex terrain. The first technical challenge undertaken by the program was an investigation of atmospheric boundary layer phenomena associated with the development, continuation and breakup of nocturnal drainage wind flows. This paper discusses the general objectives the program has addressed during the past several years and focuses on results from a major field experiment conducted in 1980 in The Geysers area of northern California. Specifically, results from measurements of simultaneous tracer releases are compared to calculations from a mass-consistent wind field model coupled to a particle-in-cell transport and diffusion model. Results of these comparisons show that model calculations agree with measurements within a factor of 5 approximately 50 percent of the time. Part of the difficulty faced by the models in these comparison studies is associated with large variabilities between measurements made by samplers located one or two δx apart when compared to the resolution of the models. Space and time averaging improves the comparisons considerably, although the design of the field experiment did not allow the determination of optimum spacial and temporal averages.