A computational framework for analyzing flow blockage in plate-type fuel channels with two-phase flow and melt transport

Plate-type fuel assemblies in high-flux research reactors are susceptible to flow blockage that may lead to fuel melting. Conventional system codes do not provide the local resolution needed for this problem, whereas full computational fluid dynamics (CFD) simulations are computationally expensive for routine accident analysis. This paper presents a computational framework for narrow rectangular plate-type fuel channels that covers the progression of a blockage event. A blockage scenario is mapped to a coupled three-dimensional solid and two-dimensional fluid model. Narrow-channel closures describe two-phase flow and critical heat flux (CHF), a dynamic porosity field updates flow accessibility, and a fully implicit scheme advances the coupled liquid, vapor, solid, and melt fields. These physical and numerical models are integrated into a broader workflow comprising model formulation, multiphysics coupling, numerical stabilization, separate-effect assessment, reactor-scale validation, and accident-scenario application. Comparisons with narrow-channel flow-boiling pressure-drop data, CHF experiments, melt/blockage and fuel-melting calculations, RA-6 heat-transfer measurements, and Japan Research Reactor-3 (JRR-3) reactor-scale results provide complementary assessment of the principal hydraulic, boiling, thermal, and material-evolution components of the framework. A transient based on the Tsinghua High Flux Reactor (THFR) then demonstrates how the same formulation follows a single modeled channel from intact forced convection through boiling and in-channel lateral redistribution to local overheating and melt transport.