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Experimental Investigations on the Four-Loop Test Facility ROCOM

Höhne, T.; Grunwald, G.; Prasser, H.-M.

Abstract

For the analysis of the core behaviour during boron dilution transients and main steam line breaks, coupled neutron kinetic / thermal hydraulic codes are necessary. These codes (e.g. DYN3D-ATHLET) must contain models of the coolant mixing on its way from the inlet noz-zles to the core entrance, because the reactivity insertion strongly depends on the distribution of temperature and boron concentration at the core inlet. The coolant mixing mainly happens in the three-dimensional flow field inside the complex geometry of the downcomer and lower plenum. The modelling of coolant mixing was carried out by detailed computational fluid dynamics (CFD) calculations with the code CFX 4.3. For the validation of the computational results, the ROCOM test facility was built, a fluid dynamic 1:5 scaled model of the Konvoi reactor. The reactor vessel is made of Plexiglas for flow visualisation and LDA measure-ments. The use of a system of wire-mesh sensors allows to measure salt concentrations at over 1000 locations with a maximum time resolution of 200 Hz. In case of stationary coolant flow in all loops a disturbance of boron concentration or temperature is transferred to a sector of the core inlet plane, which corresponds to the location of the inlet nozzle. A short plug of boron diluted water experiences a better mixing: due to the vortices in the downcomer different por-tions of the disturbance are transported with different velocities. This causes a dispersion of the front and the end of the plug (axial mixing). Further, experiments and calculations are go-ing on to investigate mixing under transient conditions (start of circulation).

  • Kerntechnik 65/5-6, S. 212-215

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