Three-dimensional looped network analysis code including core thermal analysis model for prismatic very high temperature gas-cooled reactor

The core of a prismatic very high temperature gas-cooled reactor (VHTR) is composed of stacked graphite blocks with gaps between them, which results in undesired flows through the gaps. These flows complicate the flow distribution in the reactor core and cause difficulty in predicting the temperature distribution of the graphite block. Conventionally, computational fluid dynamics (CFD) codes have been mainly used for the VHTR reactor core analysis. However, they require considerable calculation time and cost, and, therefore, are considered too expensive in terms of calculation time to investigate the effect of the gap size distribution in the core. As numerous cases with different gap size combinations need to be tested in reactor design, it can be said that high calculation speed of the design code with reasonable accuracy is an important feature. In this study, a thermo-fluid analysis code for the core of a prismatic VHTR, named FastNet (Flow Analysis for Steady-state Network), was developed for prediction of the core flow and temperature distribution with affordable computational cost. For rapid calculation, a flow network analysis method was used for flow distribution analysis, and a thermal analysis model was added to analyze the whole core temperature distribution. To overcome the drawbacks of its low resolution, an effective thermal conductivity model and a maximum fuel temperature model were applied. Finally, to verify the code, results of the FastNet calculation were compared to other codes such as the CFD code and CORONA code as a code-to-code validation. The results show that a satisfactory accuracy was obtained with a remarkably short computational time.