Rolf Lange

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.

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.

Surface Air Pollutant Concentration Frequency Distributions: Implications for Urban Modeling

With the development of ambient air quality standards (AAQS), the need arises to describe the characteristics of regional surface air-pollutant concentration frequency distributions. In the evaluation of land use plans, numerous agencies will be concerned with evaluating the effectiveness of emission zoning and/or control actions. On a regional basis, one means of performing this assessment lies in determining the changes in the pollutant frequency distributions resulting from control actions. This study presents new data concerning the surface air-pollutant concentration frequency distributions observed for area sources and continuous point sources, and compares these distributions with those of the pertinent meteorological variables describing the transport and diffusion of the pollutant. The observed surface air pollutant frequency distributions are compared to those corresponding to simple modeling concepts from either an urban area source or a continuous point source. For an urban source and a relati...

A Comparison of the Monte Carlo and the Flux Gradient Method for Atmospheric Diffusion

In order to model the dispersal of atmospheric pollutants in the planetary boundary layer, various methods of parameterizing turbulent diffusion have been employed. These approaches differ greatly in sophistication and complexity (Monin and Yaglom, 1971). Historically, the Gaussian plume models were the first dispersion models. The Gaussian formula is based on statistical theory and empirical observation of the horizontal and vertical standard deviation of the wind speed σ y and σ y . In K-theory, the Eulerian diffusion-advection equation closure problem is circumvented by assuming a gradient transport paramaterization and the postulation of the turbulent diffusivity parameter K, which must be provided empirically. The stochastic Markov chain (Monte Carlo) method employs generally the Langevin equation to model dispersion with the use of very many particles. The approach needs the empirical prescription of the wind velocity variances σ u and the Lagrangian integral time scales T L. All three methods have two things in common: they rely on some mathematical scheme and they need empirically derived diffusion parameters. (Higher order closure models are not part of this discussion.)

Atmospheric Field Experiments for Evaluating Pollutant Transport and Dispersion in Complex Terrain

The Department of Energy is currently sponsoring a program of Atmospheric Studies in Complex Terrain (ASCOT) to improve the technology needed to assess the air quality impacts of developing energy resources in areas of complex terrain. The program uses field experiments, theoretical atmospheric physics research, and mathematical models to develop a measurements and modeling methodology that can be used to provide the air quality assessments in these areas. The ASCOT team is composed of scientists from several DOE-supported research laboratories and university programs.

Plume depletion following postulated atmospheric plutonium dioxide releases.

An accidental atmospheric release of plutonium dioxide particles from a nuclear facility may result in deposition of a major fraction of the particles within a few km downwind. Estimates of plume depletion as a function of distance were computed using the atmospheric-diffusion particle-in-cell code. This code is capable of estimating the atmospheric transport, diffusion, gravitational settling, and dry deposition of the PuO, particles within a three-dimensional grid under conditions of boundary layer, stratified shear flow. The calculations show the effect on plume depletion of varying the source height, the particle size, and the type of vegetation. Pasquill F stability was chosen for applicability to nuclear facility safety analyses. The fraction of activity remaining in the plume at a given distance increases with source height and is inversely affected by surface roughness. For submicrometer particles emitted at a height of 10m, the fraction remaining airborne at 30 km downwind is about 0.5 over agricultural land covered with low growing, densely planted leafy vegetables and only 0.2 over brushland. Because of their large gravitational settling velocities, essentially all particles greater than 5 pm emitted at a 10-m height are deposited within 5 km of the facility. As the source height is increased, the effect of varying the type of vegetation becomes minimal. Hence, for a 100-m source height, the fraction of submicrometer-size particles remaining airborne is roughly 0.9 at 30 km over agricultural land as well as brushland and about 0.25 of the 5-pm particles are still airborne at 30 km.

An Intercomparison of Atmospheric Turbulence Parameters and Their Application to a Tracer Experiment Using a Monte Carlo Particle Model

Monte Carlo models simulate the dispersion of pollutants in the atmosphere by means of a large number of particles which are moved at each time step by compound velocities that take into account the mean advection component and the random turbulent fluctuations of both horizontal and vertical wind components. They are based on the solution of the Langevin equation (Gifford, 1982; Sawford, 1985) and on the assumption that wind vector fluctuations can be described by an autocorrelation process of first order (Markov process).

Emergency Response Model Evaluation Using Diablo Canyon Nuclear Power Plant Tracer Experiments

The Lawrence Livermore National Laboratory’s (LLNL) Atmospheric Release Advisory Capability (ARAC) provides real-time emergency response support for accidental radiological releases to the atmosphere at Department of Defense (DOD) and Department of Energy (DOE) facilities throughout the U.S. ARAC uses diagnostic three-dimensional (3-D) dispersion modeling as its primary emergency response tool (Dickerson and Orphan, 1976). The regional (20 to 200 km) modeling system is built around the MATHEW (Mass-Adjusted Three-dimensional Wind field) and ADPIC (Atmospheric Dispersion Particle-In-Cell) models (Sherman, 1978; Lange, 1989). MATHEW adjusts the wind field by variational methods to be mass-conservative and to account for terrain effects. ADPIC calculates the time- and space-varying transport and diffusion (using K-theory) of source material using thousands of Lagrangian “mass” particles on a Eulerian grid. To determine the accuracy and transferability of the MATHEW/ADPIC models to a wide variety of settings and meteorological conditions, the models have been evaluated against numerous tracer experiments over the last decade (Dickerson and Ermak, 1988; Lange, 1989). This paper presents a model evaluation using a tracer experiment in the complex, coastal terrain of the Diablo Canyon Nuclear Power Plant.