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Some topics in nuclear aerosol dynamics

1986; Elsevier BV; Volume: 17; Issue: 1 Linguagem: Inglês

10.1016/0149-1970(86)90041-7

1878-4224

M.M.R. Williams,

Combustion and Detonation Processes

Abstract The main mechanisms for coagulation and removal of aerosol particles are reviewed in relation to their importance in the field of nuclear reactor safety. We also examine the combined effects of aerosol size and radioactive content by considering a new generalized distribution function which is a function of these two independent variables. There is a burgeoning interest in the spatial distribution of aerosol particles arising from connected compartments or due to inhomogeneities in the atmosphere caused by turbulence. Thus we have developed a new set of coupled kinetic equations which in principle allow a detailed spatial analysis to be carried out provided certain details of the associated fluid dynamics are available. The underlying purpose of the paper is to present a relatively simple method of solving the aerosol equation without resorting to direct numerical methods. In the past, the log-normal distribution has been used to represent the aerosol volume distribution function with the amplitude, mean volume and variance being calculated from appropriate moments of the kinetic equation. Because of the poor results of the log-normal, we have investigated the accuracy of the modified Gamma distribution which contains four arbitrary parameters. A set of four coupled non-linear first order differential equations arises from this formalism and the paper discusses their solutions and how these compare with the code AEROSIM. In cases where gravitational coagulation can be neglected the results are extremely accurate, within factors of order two at long times after the initial release. With gravitational coagulation the accuracy is worse but still far superior to the log-normal distribution. Moreover the accuracy may be improved when certain numerical problems relating to machine overflow have been overcome. Results are illustrated by many Figures and Tables for a variety of coagulation mechanisms.