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Simulation der Einströmung des heißseitig eingespeisten Notkühlwassers in den Kern mit Faserablagerungen

Höhne, T.

Abstract

In 1992, strainers on the suction side of the ECCS pumps in Barsebäck NPP Unit 2 became partially clogged with mineral wool after a safety valve opened because steam impinged on the thermally-insulated equipment and released mineral wool. This event pointed out that strainer clogging in the course of a loss-of-coolant accident is an issue. Modifications of the insulation material, the strainer area and mesh size were carried out in most of the German NPPs, since the Barsebäck event . Moreover, back flushing procedures to remove the mineral wool from the strainers and differential pressure measurement were implemented to assure the performance of emergency core cooling during the containment sump recirculation mode. Nevertheless, it cannot be completely ruled out, that a limited amount of small fractions of the insulation material is transported into the RPV. During a postulated cold leg LOCA with hot leg ECC injection, the fibres enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might affect the ECC flow into the core and could result in degradation of core cooling.
The CFD simulations show that after starting the sump mode, the ECC water injected through the hot legs flows down into the core at so-called “brake through channels” located at the outer core region where the downward leg of the convection role had established. The hotter, lighter coolant rises in the center of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the break through zones. This means that the fibres are not uniformly deposited over the core cross section.

Keywords: Strainer; Core; RPV; CFD

  • Lecture (others)
    Fachkolloquium zum BMWi-Vorhaben 150 1363 "Isolationsmaterialbelastete Kühlmittelströmung", 03.03.2010, Forschungszentrum Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14559