Fully Implicit Conjugate Heat Transfer Analysis of the ARC-class Vacuum Vessel

A coupled simulation of fusion device blankets, including neutronics, thermal hydraulics, and thermo-mechanics is expected to speed up the design cycle of fusion device concepts. In this work, we demonstrate tight implicit coupling of conjugate heat transfer, using the open-source computational fluid dynamics software OpenFOAM for thermo-fluid mechanics, and Diablo for thermo-solid mechanics. The heat transfer analysis is performed by volumetric energy deposition from neutronic calculations using the Monte Carlo N-particle code on both solid and fluid parts of the vacuum vessel. An additional heat flux is imposed on the first wall, estimated from the design power of the device. The tight coupling is realized through the open-source coupling library preCICE, and it was tested on the vacuum vessel of the ARC-class tokamak design by Commonwealth Fusion Systems. The features of the coupling and the influence of different coupling parameters such as coupling schemes, acceleration techniques and convergence criteria are discussed. The coupled simulation results are compared to a thermal hydraulics simulation that includes only the fluid domains (the liquid immersion molten salt blanket and cooling channel) to demonstrate the usefulness of the coupled simulation. Further analysis was performed to identify hot spots for subsequent design improvement. This work introduces a concept for integrating conjugate electromagnetics and fluid/solid mechanics (e.g., allowing for deformation of the cooling channel walls) with our present approach for future analysis.