Advanced High Temperature Gas-Cooled Reactor Systems

Three systems have been proposed for advanced high-temperature gas-cooled reactors: a supercritical carbon dioxide $(S-CO2)$ gas turbine power conversion system, a new microchannel heat exchanger (MCHE), and a once-through-then-out (OTTO) refueling scheme with burnable poison (BP) loading. A $S-CO2$ gas turbine cycle attains higher cycle efficiency than a He gas turbine cycle because of reduced compression work around the critical point of $CO2$⁠. Considering temperature reduction at the turbine inlet by $30°C$ through intermediate heat exchange, the $S-CO2$ indirect cycle achieves an efficiency of 53.8% at a turbine inlet temperature of $820°C$ and a turbine inlet pressure of 20 MPa. This cycle efficiency value is higher by 4.5% than that (49.3%) of a He direct cycle at a turbine inlet temperature of $850°C$ and 7 MPa. A new MCHE has been proposed as an intermediate heat exchanger between the primary cooling He loop and the secondary $S-CO2$ gas turbine power conversion system and as recuperators of the $S-CO2$ gas turbine power conversion system. This MCHE has discontinuous “S-shaped” fins providing flow channels resembling sine curves. Its pressure drop is one-sixth that of a conventional MCHE with a zigzag flow channel configuration, but it has the same high heat transfer performance. The pressure drop reduction is ascribed to suppression of recirculation flows and eddies that appear around bend corners of the zigzag flow channels in the conventional MCHE. An optimal BP loading in an OTTO refueling scheme eliminates the shortcoming of its excessively high axial power peaking factor, reducing the power peaking factor from 4.44 to about 1.7, and inheriting advantages over the multipass scheme because it obviates reloading in addition to fuel handling and integrity checking systems. Because of the power peaking factor reduction, the maximum fuel temperatures are lower than the maximum permissible values of $1250°C$ for normal operation and $1600°C$ during a depressurization accident.