Integrated Aerosol and Thermalhydraulic Modelling

Abstract

Modelling of nuclear aerosol transport and deposition has traditionally has two distinct focal points: behaviour in the primary circuit where the source of aerosol is the vapour generated from overheated fuel and the release of aerosol is to containment; and behaviour in containment where the source is the aerosol released from the primary circuit and the release is through leak paths in containment to the outside atmosphere. In both cases, it has been customary to calculate aerosol behaviour from predetermined gas flow, pressure, and temperature data. In recent years it has become recognized that aerosol behaviour is intimately coupled to the thermalhydraulics and that integrated models are necessary for accurate analyses. Two examples stand out: the RAFT code for light water reactor (LWR) primary circuit analysis which includes homogeneous nucleation of released fuel material vapours to form aerosols (but without feedback on pressures and temperatures); and the CONTAIN code for LWR containment analysis which includes steam condensation for aerosol particle growth and its affect on local thermalhydraulics. Equivalent models are required for CANDU PHWR safety analyses. The aim of our analytical program is to embed aerosol physics models in the two-fluid code CATHENA used for state-of-the-art thermal- hydraulics analysis of CANDU-PHWR primary circuits (and with some modification, thermalhydraulic analysis of CANDU containments) and perform integrated analysis. To this end, we have coupled the RAFT code with CATHENA to permit complete interaction of aerosol physics and thermalhydraulic behaviour at each time step during a postulated accident. This paper describes the coupling and the program we are undertaking to optimize the coupling, with the goal of obtaining an integrated model for analysis of nuclear aerosol behaviour in CANDU primary circuits and containments.