An open-source finite element toolbox for anisotropic creep and irradiation growth: Application to tube and spacer grid assembly

TL;DR

This paper introduces an open-source interface coupling a micromechanical VPSC model with the finite element solver Code_Aster, enabling detailed simulation of anisotropic creep and irradiation growth in nuclear materials, demonstrated on a PWR spacer grid.

Contribution

It provides a novel, automated method for integrating grain-level anisotropic behavior into structural FEM simulations, specifically for nuclear reactor components.

Findings

Crystallographic texture influences clearance evolution in spacer grids.

High prismatic plane orientation reduces wear and clearance.

The framework accurately captures micromechanical responses under irradiation.

Abstract

This work presents an open-source interface that couples the viscoplastic self-consistent (VPSC) model capable of simulating anisotropic creep and irradiation growth in polycrystalline materials with the finite element solver Code_Aster. The interface enables the simulation of the micromechanical response of irradiated zirconium alloy components by integrating grain-level constitutive behavior into a structural FEM framework. A key feature is the automated rotation of stress and strain tensors between the global FEM frame and the local crystallographic axes, a transformation not natively supported by Code_Aster. The elastic strain is recovered analytically using the inverse of the self-consistently stiffness tensor provided by VPSC. As a demonstration, the framework is applied to an actual model of a pressurized water reactor (PWR) spacer grid, based on a patented design, capturing nonlinear contact and the anisotropic response of the cladding and grid. Simulations reveal the micromechanisms controlling the evolution of clearance between components and highlight the role of crystallographic texture in mitigating wear. In particular, a texture with a high fraction of prismatic planes oriented in the normal direction of the grid appears to be the most suitable for spacer design, as it minimizes clearance and contributes to wear resistance. The interface offers a flexible, extensible platform for high-fidelity simulations in nuclear fuel performance analysis.