Mechanical Model for a Full Fusion Tokamak Enabled by Supercomputing

TL;DR

This paper presents a high-fidelity finite element model of a fusion tokamak, leveraging supercomputing to simulate mechanical stresses, deformations, and vibrations, aiding in reactor design and safety assessments.

Contribution

It introduces a large-scale FEM model of a fusion reactor using supercomputing, enabling detailed structural analysis and stress distribution predictions.

Findings

Model handles 127 million finite elements with 800 processors.

Predicted deformations align with observed data.

Assesses mechanical vibrations from disturbances.

Abstract

Determining stress and strain in a component of a fusion power plant involves defining boundary conditions for the mechanical equilibrium equations, implying the availability of a full reactor model for defining those conditions. To address this fundamental challenge of reactor design, a finite element method (FEM) model for the Mega-Ampere Spherical Tokamak Upgrade (MAST-U) fusion tokamak, operating at the Culham Campus of UKAEA, has been developed and applied to assess mechanical deformations, strain, and stress in the full tokamak structure, taken as a proxy for a fusion power plant. The model, handling 127 million finite elements using about 800 processors in parallel, illustrates the level of fidelity of structural simulations of a complex nuclear device made possible by the modern supercomputing systems. The model predicts gravitational and atmospheric pressure-induced deformations in broad agreement with observations, and enables computing the spectrum of acoustic vibrations of a tokamak, arising from mechanical disturbances like an earthquake or a plasma disruption. We introduce the notion of the density of stress to characterise the distribution of stress in the entire solid body of the tokamak, and to predict the magnitude and locations of stress concentrations. The model enables defining computational requirements for simulating a whole operating fusion power plant, and provides a digital foundation for the assessment of reactor performance as well as for specifying the relevant materials testing programme.