Integrated multiphysics assessment of grid-to-rod fretting mitigation: enhancing nuclear safety through improved fuel integrity

Abstract

Grid-to-rod fretting (GTRF) represents a persistent challenge to the mechanical integrity and service life of nuclear fuel assemblies across various reactor technologies. As a leading cause of fuel failures in pressurized water reactors and a growing concern in other light water reactor systems, GTRF has drawn significant attention from both experimental and computational communities. Recent investigations have expanded in scope and precision, with advances in multiphysics simulation frameworks, in-reactor diagnostics, and surface-engineered cladding materials. These studies have illuminated complex dependencies on flow turbulence, spacer grid geometry, contact dynamics, and material behavior under irradiation, yet several technical uncertainties continue to limit predictive confidence. This work presents a comprehensive synthesis of developments surrounding GTRF, highlighting current approaches that span high-resolution fluid-structure interaction modeling, fretting-wear characterization, and emerging mitigation strategies. Specific phenomena such as fretting wear response under variable coolant conditions, coating-induced changes in contact fatigue, and the evolving mechanical role of spacer supports are examined through a multidisciplinary lens. While no single mechanism dominates across all contexts, the convergence of insights from structural mechanics, tribology, and reactor operation points toward integrated pathways for addressing the problem. GTRF arises from tightly coupled turbulent forcing, nonlinear rod-support dynamics and evolving material states. Integrated LES→FSI→wear pipelines, validated against autoclave and flow-loop experiments, offer the most promising path toward predictive life-assessment. It was recommended that coordinated high-burnup testing, open benchmark datasets, and development of reduced-order multiphysics tools with uncertainty quantification to enable quantified life-predictions for advanced claddings and higher-burnup operation. Viewing GTRF as a systems-level challenge highlights its implications for fuel reliability and safety and underscores the need for focused research to achieve quantitative, licensing-grade predictions.