Progressive Multiphysics analysis to Implement a ceramic gas gap thermal barrier Enabling High-Temperature irradiation of High-Burnup fuel rods

To address the irradiation testing requirements of high-temperature high-burnup fuel rods (HT-HBFR) in low-temperature, low-pressure research reactors, this study proposes an irradiation assembly incorporating a ceramic gas-gap thermal barrier (CGGTB) to mitigate localized overheating in the reactor core. Heat transfer simulations demonstrated that, within a heat flux range of 1,000 ± 200 W/m², the maximum deviation between experimental and theoretical values was –3.76 %, confirming the engineering feasibility of the thermal barrier and it has high predictive accuracy under anticipated operational conditions. Further theoretical calculations, numerical simulations, and hydraulic experiments were conducted to optimize the throttling device geometry and coolant channel parameters. At a target flow rate of 0.854 kg/s, the theoretical pressure drop of the downward coolant flow through the irradiation device exceeded the experimental value by 9.46 %. Progressive multiphysics simulations systematically validated the decoupling control capability of the CGGTB over fuel pellet temperature, cladding surface temperature, and coolant interface temperature. Under a rated heat flux of 1,000 kW/m², the maximum fuel pellet temperature reached 1,259 ℃ and the cladding surface temperature was 615 ℃, both satisfying the test requirements, while the coolant outlet temperature remained at 53.3 ℃, well below the thermal safety limit (195 ℃) of the High Flux Engineering Test Reactor (HFETR). This irradiation strategy provides high-precision technical support for the performance verification of HT-HBFR in non-prototype reactor environments.