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Thermal-Spectrum Reactors
Very-High-Temperature Reactor (VHTR)
The VHTR system uses a thermal neutron spectrum and a once-through uranium cycle. The reference reactor concept has a 600 MWth helium-cooled core based on either the prismatic block fuel of the Gas Turbine - Modular Helium Reactor (GT-MHR) or the pebble fuel of the Pebble Bed Modular Reactor (PBMR). The primary circuit is connected to a steam reformer/steam generator to deliver process heat. The VHTR system has coolant outlet temperatures above 1000°C. It is intended to be a high-efficiency system that can supply process heat to a broad spectrum of high-temperature and energy-intensive non-electric processes. The system may incorporate electricity generation equipment to meet cogeneration needs. The system also has the flexibility to adopt U/Pu fuel cycles and offer enhanced waste minimization. The VHTR system is primarily envisioned for missions in hydrogen production and other process-heat applications, although it could produce electricity as well.
Supercritical-Water-Cooled Reactor (SCWR)
The SCWR system features two fuel cycle options. The first is an open cycle with a thermal neutron spectrum. The second option is a closed cycle with a fast-neutron spectrum reactor with full actinide recycle. Both options use a high-temperature high-pressure water-cooled reactor that operates above the thermodynamic critical point of water (22.1 Mpa, 374°C) to achieve a thermal efficiency approaching 44 percent. The fuel cycle for the thermal option is a once-through uranium cycle. The fast-spectrum option uses central fuel cycle facilities based on advanced aqueous processing for actinide recycle.
In either option, the reference plant has a 1700 MWe power level, an operating pressure of 25 Mpa, and a reactor outlet temperature of 550°C. Passive safety features similar to those of the simplified boiling water reactor are incorporated. Owing to the low density of supercritical water, additional moderator is added to thermalize the core in the thermal option. The SCWR system is primarily envisioned for missions in electricity production with a possible option for actinide management.
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