Heat loss from Re-Entrant fuel channel in a 1200-MW_el pressure channel SCWR

Generation III and III+ reactors are currently in operation globally and Generation IV (Gen IV) reactor designs are being developed. There are six Generation IV nuclear systems under development worldwide, namely, Very High Temperature Reactor (VHTR), Molten Salt Reactor (MSR), Gas-cooled Fast Reactor (GFR), Sodium-cooled Fast Reactor (SFR), Lead-cooled Fast Reactor (LFR) and SuperCritical Water-cooled Reactor (SCWR). Of these six systems, Canada has decided to pursue the SCWR as its choice for a Gen IV reactor. One major advantage of the SCWR is an increase in thermal efficiency from the 30-35% range of current nuclear power plants to approximately 40-45%. SCWRs operate well above the critical point of water at a pressure of 25 MPa and reactor outlet temperatures up to 650°C. Due to the operating conditions, current fuel-channel designs cannot be used in the SCWR and new fuel-channel design concepts are under development. One such concept is called the Re-Entrant Channel (REC). The REC is a vertical channel and consists of two tubes, the inner (flow) tube and the pressure tube. The inner tube is hollow and the fuel bundles and insulator are located in the pressure tube. An annulus is formed between the flow and pressure tubes. A perforated liner is used to protect the insulator from the fuel-string, and the pressure tube is in contact with the moderator. The coolant flows from the top of the channel to the bottom via the flow tube and then reverses its direction and flows upwards through the pressure tube. The objective of this work is to determine the heat loss from a REC for a generic 1200-MW_el SCWR. A one-dimensional numerical model was developed in MATLAB to calculate the temperature profiles, the heat transfer coefficients and the heat loss from the coolant to the moderator for a given set of flow, pressure and temperature boundary conditions. With the results from the numerical model, the design of the REC can be optimized to improve the efficiency. (author)