Simple aerosol modelling for fusion power plant containments

The modelling of the transport and depletion of aerosols in fusion power plant containment volumes is an important part of the analysis of postulated accidents. This has hitherto been performed either by very over-simplified and over-conservative calculations or by the use of large codes which are time-consuming and inflexible to use, and do not readily lead to understanding. These large codes make quite heavy demands on computer resources because they have to calculate agglomeration and removal rates, as well as number densities of aerosol particles with a distribution of sizes. This paper describes a method of taking these particle growth and mass depletion effects into account by transforming the problem into one of calculating the behaviour of a monodisperse aerosol of constant size which is defined by the geometry of the containment system and the total mass of aerosol present initially. Results were obtained for a number of test cases and compared with calculations for the same cases carried out using ITHACA. The agreement between the two methods was found to be excellent. Further calculations for a more comprehensive range of conditions were also carried out with the proposed model and the results presented. These extended calculations illustrate the fact that even significantly damaged containments (signified by a high leak rate) can, depending on the conditions, bring about retention of nearly all the aerosol by gravitational settling.