Aerosol behaviour in spaces with a heated pool of sodium on the floor

Aerosol behaviour in the inner containment is an important part of the source term of nuclear reactor accidents. A hypothetical core disruptive accident with an LMFBR like SNR 300, releases a large amount of aerosol to the inner containment which is filled with nitrogen as an inert gas. The core remains covered by sodium. Simplified, the post-accident situation implies an inner containment with a heated pool of sodium on the floor and above it aerosol resulting from the nuclear excursion and from reaction of sodium vapour with nitrogen impurities (O2 and H2O). The aerosol will be removed by the process of stirred settling. During removal the remaining aerosol will grow continuously due to the vapour supply by the heated pool. This system has been analyzed theoretically and a model (MADCA) was obtained predicting behaviour of aerosols from an instantaneous source in such condensing vapour systems. The MADCA model was validated by means of aerosol experiments in atmospheres of condensing vapour of water or sodium. A continuous aerosol source can also be taken into account by incorporation of this term in the basic differential equations of the MADCA model. Aerosol formed by the sodium pool or by reaction of sodium vapour with water desorbed from heated concrete walls, may comprise such continuous sources. (author)