A Specialized Thermal-hydraulic Code with Porous Media Model and SIMPLEC Algorithm for PB-FHRs

摘要

Pebble bed fluoride-salt cooled high temperature reactors (PB-FHRs) are Generation Ⅳ reactors which use coated particle pebble fuels and liquid fluoride-salt coolants. Thermal-hydraulics analysis of reactor core is significant for both design and safety issues. A specialized code for core thermal-hydraulics analysis is very important for this novel reactor, which is also needed in detailed transient analysis. Aim of this study is to develop a thermal-hydraulic code (named GATH) based on CFD method for PB-FHRs to analyze thermal-hydraulic phenomena in reactor core. Porous media model is applied to simplify reactor geometry. Energy equations for solid region and fluid region are constructed respectively with considering local thermal non-equilibrium effect between fuels and coolants. Macroscopic mass and momentum equations are solved to get speed distribution and pressure drop of liquid by using SIMPLEC algorithm. The thermal dispersion mechanism in the pebble bed is considered by solving modified macroscopic turbulence equations with additional source terms. Empirical correlations are used to calculate effective heat conductivity of pebble bed, resistance terms and heat transfer coefficient. A simplified PB-FHR model is analyzed by GATH. The results indicate that the resistance term of porous media has a significant influence on pressure drop. Heat transfer coefficient and effective heat conductivity has a significant influence on temperature distribution. Calculation results from GATH are compared with a commercial CFD code named FLUENT. Good agreement between the two codes indicates the adopted methods in GATH are rational. GATH can be employed for thermal-hydraulic analysis of PB-FHRs.