Small and long-life high temperature gas-cooled Reactors (HTRs) are interesting because they can safely produce electricity or heat for remote areas or industrial users in developed and/or developing countries. Small HTRs have the advantages of transportability, modular construction, and flexible site selection. This paper presents the neutronic analysis of the U-Battery®, which is a small, long-life and block-type HTR based on currently mature HTR technologies. The 3.5 meter diameter of the reactor pressure vessel (RPV) is one of the design restrictions in order to secure its transportability. The lifetime of the U-Battery® is chosen to be 5 to 10 years in order to reduce its operating and maintenance costs. Key design parameters and possible core layouts of the U-Battery® were parametrically investigated using the TRITON 6 module in SCALE 5.1. The design parameters analyzed include fuel enrichment, the packing fraction of the TRISO particles, the radii of the fuel compacts and kernels, and the thicknesses of the top and bottom reflectors. The external side reflector, located outside the RPV of the U-Battery®, is proposed to improve neutron economy because the U-Battery® adopts a thin internal side reflector located inside the RPV. Possible layouts of the U-Battery® cover cylindrical cores and annular cores. Since the energy conversion system of the U-Battery® is supposed to be based on a Rankine cycle, the effect of steam or water on the reactivity was also investigated because water ingress is a design-basis accident for HTRs. The analysis shows that the design of the U-Battery® is feasible and flexible from neutronics point of view. The core layouts of 37*4(4 layers of 37 blocks), 30*4 and 19*4 are promising designs of the U-Battery®. Further thermal-hydraulic evaluations to these promising layouts are ongoing.

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