Plume Depletion Following Postulated Atmospheric Plutonium Dioxide Releases

Abstract

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.

Environmental consequences of postulated radionuclide releases from the Battelle Memorial Institute Columbus Laboratories JN-1b Building at the West Jefferson site as a result of severe natural phenomena

“…The deposition velocity of plutonium particles cannot be specified exactly because it will vary depending on the size distribution of the particles, the nature of the surface on which deposition occurs, the wind speed, and other meteorological variables. The deposition velocity for plutonium has been reported to range from 1 x 10-4 to 3 x 10-2 m/sec (Selby et al 1975, Cohen 1977, Baker 1977, Gudiksen et al 1976. A value of 1 x 10-3 m/sec is used in this report (Baker 1977).…”

Environmental consequences of postulated plutonium releases from Exxon Nuclear MOFP, Richland, Washington, as a result of severe natural phenomena

“…The deposition velocity of plutonium particles cannot be specified exactly because it will vary depending on the size distribution of the particles, the nature of the surface on which deposition occurs, the wind speed, and other meteorological variables. The deposition velocity for plutonium has been reported to range from 1 x 10-4 to 3 X 10-2 m/sec (Selby et al 1975, Cohen 1977, Baker 1977, Gudiksen et al 1976, FES 1974. A value of 1 x 10-3 m/sec is used in this report (Baker 1977).…”

Environmental consequences of postulated plutonium releases from General Electric Company Vallecitos Nuclear Center, Vallecitos, California, as a result of severe natural phenomena

“…(2 ) W. • the concentration of radionuclide i on the ground surface, Vg/m2 The deposition velocity of plutonium particles cannot be specified exactly because it will vary depending on the size distribution of the particles, the nature of the surface on which deposition occurs, the wind speed, and other meteorological variables. The deposition velocity for plutonium has been reported to range from 1 x 10-4 to 3 x 10-2 m/sec (Selby et al 1975, Cohen 1977, Baker 1977, Gudiksen et al 1976. A value of 1 x 10-3 m/sec is used in this report (Baker 1977).…”

“…The location of the maximum exposed individual would 5.6E-07 9.9E-07 1 .2E-05 7.3E-10 probably be a few hundred meters from the point of release. and the inclusion of cloud depletion would only lower the doses by a few percent (USNRC Guide 1.1111977, Gudiksen 1976).…”