Fuel, core design and subchannel analysis of a superfast reactor

A compact supercritical water-cooled fast reactor (superfast reactor) core with a power of 700 MWe is designed by using a three-dimensional neutronics thermal-hydraulic coupled method. The core consists of 126 seed assemblies and 73 blanket assemblies. In the seed assemblies, 251 fuel rods, consisting of MOX pellets, stainless steel (SUS304) cladding, and fission gas plenum are arranged into a tight triangle lattice along with 19 guide tubes for control rods and instrumentation. A zirconium hydride (ZrH) layer is employed in the blanket assemblies to reduce void reactivity. The results of the coupling three-dimensional neutronics and thermal hydraulic calculations show that this core has a high power density of 158.8 W/cm(3) with a maximum linear heat generation rate (MLHGR) less than 39 kW/m, that an average coolant outlet temperature of 500 degrees C is achieved with a maximum cladding surface temperature (MCST) less than 650 degrees C, and that void reactivity coefficients are negative throughout the cycle. Since the thermal-hydraulic part of the core design is based on single-channel analyses, subchannel analyses are also performed on all the seed assemblies to clarify the influence of cross-flow.