table 1. SMR types. SMR Type Water-Cooled Example Design NuScale KAERI SMART Holtec SMR-160 Gas-Cooled General Atomics EM2 USNC Micro-Modular Reactor URENCO U-Battery Molten-SaltCooled Liquid-MetalCooled Terrestrial Energy IMSR-400 Moltex Energy Stable Salt Reactor LeadCold SEALER ARC-100 Rating (MWt) 250 330 525 500 15 10 400 750 8 286 Rating (MWe) 77 100 160 265 5 4 192 300 3 100 Temperature (° C) 302 323 315 850 630 750 700 650 432 510 Refueling (years) 2 3 1.5-2 30 20 5 7 continuous 30 20 One Module of an SMR Plant A conceptualized small modular high-temperature gas reactor is shown here (Figure S1). The two-vessel design links the reactor core with the steam generator through a nested pair of tubes that carry the helium coolant. The uranium fuel is in the form of carbon/silicon carbide encapsulated particles packaged into either spherical " pebbles " or prismatic assemblies that the coolant flows over. Neutron-absorbing control rods are used to regulate the reactivity in the core to adjust the thermal output power. Primary coolant circulates inside the reactor vessel using Control Rods Core Steam Turbine Helium Circulator a helium circulator, moving down through the core and extracting the heat, then flowing across to the steam generator where it transfers that heat to a secondary loop. The steam then drives a turbine, which is connected to a synchronous generator to produce electricity. The steam from the turbine outlet is condensed back into water using an external cooling loop and pumped back to the inlet of the steam generator. An additional loop and heat exchanger are used to extract heat for industrial processes or for district heating applications. Heat Exchanger Process Heat Loop Hot Helium Return Helium Steam Generator Pumps Condenser Waste Heat Loop Synchronous Generator figure S1. A conceptualized small modular high-temperature gas reactor. 60 ieee power & energy magazine march/april 2022