High temperature thermal contact conductance measurement and correlation for pressure tube and calandria tube interface under CO2 environment

•Development of a unique experimental facilityfor high temperature thermal contact conductance (TCC) estimation.•Reliable and accurate database of TCC across Pressure Tube/Calandria Tube (PT/CT) interface for PHWR is presented.•Correlation of TCC between PT/CT contact at high temperature is proposed. This investigation aims to develop a reliable and accurate experimental database for thermal contact conductance (TCC) across the sample of pressure tube (PT) and calandria tube (CT) interface. During a postulated accidental scenario of pressurized heavy water reactors (PHWR), the PT might meet CT owing to the thermomechanical deformation due to sagging, ballooning, or a combination of both. This initiates a high heat flow from the fuel bundle to PT, followed by PT to CT and further from CT to the moderator. The involvement of large heat fluxes demands the correct estimation of the associated heat transfer rate to the moderator, which largely depends on the contact conductance between PT and CT at similar working ranges. In this work, a unique experimental setup has been developed to precisely characterize interfacial interactions of the flat surfaces of PT and CT specimen subjected to axial force in the CO2 atmosphere to avoid oxidation at high temperature, which closely simulates the actual scenario of PHWR. Steady state experiments were performed under the contact pressures ranging from 0.6 to 8 MPa, whereas interfacial temperatures between PT and CT vary from 300 to 500 °C. Two-factor, three-level face-centered central composite design (CCD) was used to select the intermediate pressure and temperature parameters prior to performing the experiments. Finally, experiments were performed at the selected range of parameters and correlation for estimating TCC has been developed using Response Surface Methodology (RSM). The correlation is inherently expressed as the function of intermediate temperature and contacting pressure at PT-CT interface, which has been utilized in safety analysis codes for safety evaluation of reactors.