Authors: O. Koekemoer, C. G. du Toit
Year: 2025
Industry: Nuclear & SMR
Keywords: Use FSE, Dynamic, HTR, Validation, Comparison
ABSTRACT
The Very High Temperature Reactor’s (VHTR) inherent safety, high thermal efficiency, and high reactor outlet temperature of as high as 1000 °C has led to the development and implementation of VHTRs in process heat, hydrogen production, and power generating applications. These reactors require effective and demonstrable computational tools and methodologies for the design-, operation-, and safety analyses. However, simulating the thermal-hydraulic behavior in prismatic block reactor units poses several challenges and typically requires significant computational resources and computational times. The numerical models of prismatic block reactors must amongst others account for the thermal-fluid phenomena in the fuel compacts, graphite, coolant channels in the fuel blocks, bypass and cross gaps between fuel blocks and the mixing in the upper and lower plenums. Due to the limitations on available computing power, this amount of detail cannot be accounted for in a single explicit three-dimensional numerical model. This paper describes the development of a methodology that couples a one-dimensional (1D) systems code and a three-dimensional (3D) Computational Fluid Dynamic (CFD) code. By combining the desired features of a one-dimensional systems code and a three-dimensional CFD code, the required resources are optimized whilst still retaining an acceptable level of accuracy. The 1D/3D co-simulation methodology is demonstrated by simulating the heat transfer and fluid flow within a single-channel fuel module of a prismatic block VHTR. In the coupled 1D/3D model, the one-dimensional (1D) elements represent the tube flow within the coolant channels while the spatial elements represent the fuel-compact and graphite moderator associated with a single-channel fuel module. The coupled 1D/3D methodology was validated against corresponding values obtained from published work as well as full CFD. The coupled 1D/3D models indicate errors between the calculated fuel- and coolant temperatures for both a (i) uniform, and (ii) cosine power profile of less than 1.5%, when compared to a full CFD analysis of the same system. By explicitly coupling the 1D and 3D solvers the computational expense is greatly reduced when compared to full CFD. Therefore, the coupled 1D/3D methodology can form the basis of an integrated model for the entire prismatic core.