CFD modelling of subcooled boiling – concept, validation and application to fuel assembly design


CFD modelling of subcooled boiling – concept, validation and application to fuel assembly design

Krepper, E.; Koncar, B.; Egorov, Y.

The paper describes actual CFD (Computational Fluid Dynamics) approaches to subcooled boiling and investigates their capability to contribute to fuel assembly design. In a prototype version of the CFD code CFX a wall boiling model is implemented based on a wall heat flux partition algorithm. It can be shown, that the wall boiling model is able to calculate the cross sectional averaged vapour volume fraction of vertical heated tubes tests with good agreement to published experimental data. The most sensitive parameters of the model are identified. Needs for more detailed experiments are established which are necessary to support further model development. The model is applied for investigation of the phenomena inside a hot channel of a fuel assembly. Here the essential phenomenon is the critical heat flux. Although subcooled boiling represents only a preliminary state towards the critical heat flux occurrence, essential parameters like swirl, cross flow between adjacent channels and concentration regions of bubbles can be determined. By calculating the temperature of the rod surface the critical regions can be identified which may later on lead to departure from nucleate boiling and possible damage of the fuel pin. The application of up-to-date CFD with a subcooled boiling model for the simulation of a hot channel enables the comparison and the evaluation of different geometrical designs of the spacer grids of a fuel rod bundle.

Keywords: CFD; bubbly flow; boiling; code validation; fuel rod bundle

Permalink: https://www.hzdr.de/publications/Publ-8597
Publ.-Id: 8597