Multiphysics Modeling of Heat and Solute Transport in CRUD Using Two-Phase Film Boiling Approach

Chalk River Unidentified Deposits (CRUD) on nuclear fuel cladding present persistent challenges in pressurized water reactors (PWRs), including cladding corrosion, elevated radiation fields, and CRUD-induced power shifts (CIPS). To better understand these effects, several Multiphysics models have been developed in recent years. Building on these advances, this study introduces a fully coupled two-dimensional Multiphysics framework that integrates two-phase film boiling, solute transport, chemical equilibria, and radiolytic decomposition, a process usually overlooked in existing film boiling models. The model captures vapor film formation within CRUD under high heat flux, along with local temperature, pressure, and solute accumulation. It shows improved agreement with WALT benchmark data compared with previous models. Results indicate that boron accumulation within the CRUD increases the local saturation temperature, while pH rise at the liquid-vapor film interface promotes LiBO 2 precipitation under extreme thermal conditions. Parametric studies further reveal how deposit thickness, porosity, pore size, and chimney density influence cladding temperature, vapor film thickness, pH, and boron accumulation.