Porous media approach in thermohydraulic analysis of high temperature reactors in pressurized/depressurized cooldown: An improvement

•Thermo Hydraulic Porous Program is made to simulate block fuel elements and pebble bed reactors.•Results of the comparisons show full agreement as regards pressurized/depressurized Cooldown states.•Good agreement was revealed as orienting a 2D benchmark to PBMR-400.•Good agreement also was revealed as orienting a 2D benchmark to GT-MHR.

The current study aims at introducing a 2D and fast-running code for the issues pertinent to design, analysis and safety in modular high temperature reactors. While the porous media approach is only applied to pebble bed type, the analysis in this paper covers both pebble bed and prismatic reactor.A time-dependent mass equation along with energy conservation equation for the cooling gas and a time-dependent energy conservation equation for the solid was solved. Appropriate series of constitutive equations (e.g. heat transfer coefficient, effective heat conductivity of solid, heat transfer coefficient, pressure drop etc.) has been recruited as well. In addition a finite-volume method is employed for spatial discretization. The SIMPLET algorithm has been used to solve the velocity and pressure linked to the momentum equation. The method of SIMPLET for natural convection is lot more advantageous over the SIMPLE method and will improve the results. Our developed code utilizes advantages of both Zehner and Schlünder and Kasperek and Vortmeyer models which lead to better results. In addition, in Thermo Hydraulic Porous Program (THPP), the Rhie-Chow technique is also used to correct the velocity components while dealing with the discretization problem of the pressure gradient. In the codes developed so far, staggered grids is usually used in computations. However, here we have adopted most of the advantages of Rhie-Chow technique in precision and computational cost.Making use of some simplified assumptions made by the benchmark definition, the core has been modeled in form of 2D-geometry. The calculations below deal with the loss of cooling accidents with or without depressurization. Having compared 2D results of THPP, the well-established thermal-hydraulics codes of THERMIX (Banaschek, 1983) and TH3D (Hossain, 2008) to simulate pebble bed and block fuel elements, it becomes clear that regarding the transient behavior during a depressurized loss of coolant accident, there exists a good agreement. Besides, there were detected more considerable differences between the results of the two codes regarding the pressurized loss of cooling accident. The program code shall be generally applicable for modular High Temperature Reactors (HTRs) e.g. pebble fuel and block fuel elements.