Sump simulations

Mineral wool insulation material applied to the primary cooling circuit of a nuclear reactor maybe damaged in the course of a loss of coolant accident (LOCA). The insulation material released by the leak may compromise the operation of the emergency core cooling system (ECCS), as it maybe transported together with the coolant in the form of mineral wool fiber agglomerates (MWFA) suspensions to the containment sump strainers, which are mounted at the inlet of the ECCS to keep any debris away from the emergency cooling pumps. In the further course of the LOCA, the MWFA may block or penetrate the strainers. In addition to the impact of MWFA on the pressure drop across the strainers, corrosion products formed over time may also accumulate in the fiber cakes on the strainers, which can lead to a significant increase in the strainer pressure drop and result in cavitation in the ECCS. Therefore, it is essential to understand the transport characteristics of the insulation materials in order to determine the long-term operability of nuclear reactors, which undergo LOCA. An experimental and theoretical study performed by the Helmholtz-Zentrum Dresden-Rossendorf and the Hochschule Zittau/Görlitz1 is investigating the phenomena that maybe observed in the containment vessel during a primary circuit coolant leak. The study entails the generation of fiber agglomerates, the determination of their transport properties in single and multi-effect experiments and the long-term effects that particles formed due to corrosion of metallic containment internals by the coolant medium have on the strainer pressure drop. The focus of this presentation is on the numerical models that are used to predict the transport of MWFA by CFD simulations in the containment sump. Two dispersed phases were conditions to determine the influence of entrained air from a jet on the transport of fibre agglomerates through the sump. The strainer model of A. Grahn was implemented to observe the impact that the accumulation of the fibres have on the pressure drop across the strainers. The geometry considered is similar to the containment sump configurations found in Nuclear Power Plants

Simulations of agglomerate sedimentation and suspension

Mineral wool insulation material applied to the primary cooling circuit of a nuclear reactor maybe damaged in the course of a loss of coolant accident (LOCA). The insulation material released by the leak may compromise the operation of the emergency core cooling system (ECCS), as it maybe transported together with the coolant in the form of mineral wool fiber agglomerates (MWFA) suspensions to the containment sump strainers, which are mounted at the inlet of the ECCS to keep any debris away from the emergency cooling pumps. In the further course of the LOCA, the MWFA may block or penetrate the strainers. In addition to the impact of MWFA on the pressure drop across the strainers, corrosion products formed over time may also accumulate in the fiber cakes on the strainers, which can lead to a significant increase in the strainer pressure drop and result in cavitation in the ECCS. Therefore, it is essential to understand the transport characteristics of the insulation materials in order to determine the long-term operability of nuclear reactors, which undergo LOCA. An experimental and theoretical study performed by the Helmholtz-Zentrum Dresden-Rossendorf and the Hochschule Zittau/Görlitz is investigating the phenomena that maybe observed in the containment vessel during a primary circuit coolant leak. The study entails the generation of fiber agglomerates, the determination of their transport properties in single and multi-effect experiments and the long-term effects that particles formed due to corrosion of metallic containment internals by the coolant medium have on the strainer pressure drop. The focus of this presentation is on the numerical models that are used to predict the transport of MWFA by CFD simulations. A number of pseudo-continuous dispersed phases of spherical wetted agglomerates can represent the MWFA. The size, density, the relative viscosity of the fluid-fiber agglomerate mixture and the turbulent dispersion all affect how the fiber agglomerates are transported. In the cases described here, the size is kept constant while the density is modified. This definition affects both the terminal velocity and volume fraction of the dispersed phases. Application of such a model to sedimentation in a quiescent column and a horizontal flow are examined. The scenario also presents the suspension and horizontal transport of a single fiber agglomerate phase in a racetrack type channel

CFD Modellierung einer partikelbelasteten Kühlmittelströmung im Sumpf und in der Kondensationskammer

Der Bericht beschreibt die Arbeiten zur CFD-Modellentwicklung zur Beschreibung des Fasertransportes in einer Wasserströmung, die im Unterauftrag der Hochschule Zittau/Görlitz erfolgten. Während die experimentellen Arbeiten zu dieser Thematik in Zittau durchgeführt wurden, lag der Schwerpunkt der theoretischen Arbeiten in Rossendorf. Im Arbeitspunkt EZ 1 des Projektantrages ist die Erweiterung der Einzeleffektuntersuchungen vorgesehen. Die entsprechenden Modellansätze zum Partikeltransport sind im Kapitel 3.1. beschrieben. Die Modellanpassung und Validierung ist in 3.2 und 3.3 dargestellt. Der Fasertransport in einer Wasserströmung wird durch Jet-Phänomene bestimmt. Untersuchungen dazu sind im EZ3.1 des Projektantrages: „3D-Phänomene infolge Blasenmitriss“ vorgesehen und die Modellansätze und der Vergleich zu Experimenten in den Kapiteln 4.1 bis 4.3 dargestellt. Des Weiteren wird der Einfluss auf den Ausgleich der Temperatur für den Fall untersucht, dass der Jet kälter als die Wasservorlage im Tank ist. Dieser Abschnitt entspricht damit der EZ3.2 des Antrages: „3D-Phänomene infolge Temperaturdifferenzen. Im Kapitel 4.4 wird auf die Strömungsvorgänge in der Zittauer Strömungswanne eingegangen und damit der Punkt EZ4 des Antrages: Integraluntersuchungen bearbeitet. Kapitel 5 beschreibt die Entwicklung eines Sieb-Modells, das die Faser-Kompaktierung berücksichtigt und auf der Darcy-Gleichung basiert. Die Modellparameter werden an Experimenten in Zittau justiert. Diese Experimente wurden für verschiedene Materialien durchgeführt und mit deren Hilfe ein Koeffizientenkatalog erstellt. Das Modell wurde in den CFD-Code CFX implementiert und anhand einiger Anwendungsbeispiele demonstriert

Fibre agglomerate transport in a horizontal flow

An experimental and theoretical study of the transport of mineral wool fibre agglomerates in nuclear power plant containment sumps is being performed. A racetrack channel was devised to provide data for the validation of numerical models, which are intended to model the transport of fibre agglomerates. The racetrack channel provides near uniform and steady conditions that lead to either the sedimentation or suspension of the agglomerates. Various experimental techniques were used to determine the velocity conditions and the distribution of the fibre agglomerates in the channel. The fibre agglomerates are modelled as fluid particles in the Eulerian reference frame. Simulations of pure sedimentation of a known mass and volume of agglomerations show that the transport of the fibre agglomerates can be replicated. The suspension of the fibres is also replicated in the simulations; however, the definition of the fibre agglomerate phase is strongly dependent on the selected density and diameter. Detailed information on the morphology of the fibre agglomerates is lacking for the suspension conditions, as the fibre agglomerates may undergo breakage and erosion. Therefore, ongoing work, which is described here, is being pursued to improve the experimental characterisation of the suspended transport of the fibre agglomerates

On the Convective Stability and Pattern Formation of Volumetrically Heated Flows with Asymmetric Boundaries

Non-linear solutions and their stability are presented for homogeneously heated fluids bounded by rigid conducting and insulating plates. In particular, we sought roll-type solutions emerging from the neutral stability curve for fluids with Prandtl numbers of 0.025, 0.25, 0.705, and 7. We determined the stability boundaries for the roll states in order to identify possible bifurcation points for the secondary flow in the form of regions that are equivalent to the Busse balloon. We also compared the stability exchange between ‘‘up’’ and ‘‘down’’ hexagons for a Prandtl number of $$0.25$$ obtained from weakly non-linear analysis in relation to the fully non-linear analysis, consistent with earlier studies. Our numerical analysis showed that there are potential bistable regions for both hexagons and rolls, a result that requires further investigations with a fully non-linear analysis