Influence of the Shape of Tube break on the Aerosol retention during severe accident SGTR secuences: An experimental investigation under the International Artist2 Project

The potential radioactive release to the environment in case of meltdown sequences with steam generator tube ruptures, turns this type of by-pass sequences into an indispensable scenario to model when assessing PWR risk. Despite the recent investigation effort conducted through international projects, like EU-SGTR (Auvinen et al, 2005) and ARTIST (Guntay et al, 2004), the existing data are still scarce and need to be extended to build up a sound database on which to develop further understanding and modelling capabilities. In the case of the lack of water in the secondary side, some radioactive retention is still feasible given the huge amount of structural surfaces available on the particles pathway through towards the environment (tube surfaces, dryers, separators, etc.). Beyond any doubt, the break stage is highly relevant not just because of its own retention capability but also because of its capability of affecting properties of aerosols as important as their size distribution. Nonetheless, the amount of aerosols scrubbed in a dry break stage is a function of some boundary conditions, like the particle size and nature, the gas flow rate and the form of the tube breach. CIEMAT, in collaboration with other ARTIST2 partners and under the sponsorship of the Spanish Nuclear Council (CSN), has launched an experimental program to address some of these issues. The expected final outcome will be a more thorough CIEMAT SGTR database, which supplements the one under construction at PSI, who is actually running the ARTIST projects. This paper presents the experimental Ciemat Artist2 Aerosol Test (CAAT2) campaign with particular emphasis on the effect of breach shape on aerosol retention. In addition, the update of the SGTR-PECA facility of the LASS (Laboratory of Analysis of Safety Systems) at CIEMAT, will be shortly described. In order to illustrate the type of information expected from this second experimental phase at CIEMAT, the results from the first fish-mouth test (CAAT2-3) will be given and compared to those previously gathered under similar conditions with a guillotine breach (Velasco et al, 2010).