In the development of the supercritical water-cooled reactor (SCWR), an in-pile fuel assembly test loop has been designed within the framework of the joint Chinese–European project, called SCWR-FQT (Fuel Qualification Test). This paper presents the basic design of the loop with its auxiliary and safety systems, which has been examined in detail by thermal-hydraulic analyses in order to achieve operation of the loop above the thermodynamic critical point of water (374°C, 22.1 MPa) and checked by stress analyses to assure safe operation. The designed experimental loop for fuel qualification in supercritical water consists of a closed pressurized water circuit with forced circulation of the coolant through the test section—the active channel which is intended to be installed into the existing research pool-type reactor LVR-15. The active channel will be operated at temperatures and pressures which are typical for the high-performance light water reactor (HPLWR). A thick-walled pressure tube made from austenitic stainless steel, which is able to withstand the high system pressure, encloses the active channel. It contains four fuel rods with $UO2$ (enrichment of 19.7% $U235$) with a total heating power of $∼64 kW$ and a recuperator in order to achieve hot channel conditions as they are expected to occur in the evaporator of the HPLWR. The internal flow is realized so as to prevent the creep condition of the pressure tube. An internal U-tube cooler serves as heat sink and is connected to the secondary circuit. The entire active channel is isolated from water of the reactor pool by an air gap between the pressure tube and an aluminum displacer. The test section with fuel is connected to a 300°C closed loop and to a primary pump located outside the reactor building as well as safety systems and auxiliary systems, such as purification and measurement circuits, which are all connected with the primary circuit.

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