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Generation IV International Forum LogoVery-High-Temperature Reactor (VHTR)
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The VHTR reference concept will be a helium-cooled, graphite moderated, thermal neutron spectrum reactor with a design goal outlet temperature of 1000°C or higher.

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The reactor core could be either a prismatic graphite block type core or a pebble bed core; the final selection of a reference core concept will be made following completion of the preconceptual designs for each. The VHTR will produce both electricity and hydrogen. The process heat for hydrogen production will be transferred to the hydrogen plant through an intermediate heat exchanger (IHX). The reactor thermal power (about 600 MWt) and core configuration will be designed to assure passive decay heat removal without fuel damage during accidents. The fuel cycle will be a once-through very high burnup low-enriched uranium fuel cycle.

The basic technology for the VHTR has been established in former high temperature gas-cooled reactor plants (DRAGON, Peach Bottom, AVR, THTR, Fort St. Vrain). In addition, the technologies for the VHTR are being advanced in the Gas Turbine-Modular Helium Reactor (GT-MHR) Project, and the South African state utility ESKOM sponsored project to develop the Pebble Bed Modular Reactor (PBMR). Furthermore, the Japanese HTTR and Chinese HTR-10 projects are demonstrating the feasibility of some of the planned VHTR components and materials. (The HTTR is expected to reach a maximum coolant outlet temperature of 950°C in 2003.) Therefore, the VHTR project is focused on building a demonstration reactor, rather than simply confirming the basic feasibility of the concept.

One or more processes will use heat from the high temperature helium coolant to produce hydrogen. The first process of interest is the thermo-chemical splitting of water into hydrogen and oxygen. The primary candidate thermo-chemical process is the sulfur-iodine (SI) process. The second process of interest is thermally assisted electrolysis of water. The high efficiency Brayton cycle enabled by the VHTR may be used to generate the hydrogen from water by electrolysis. The efficiency of this process can be substantially improved by heating the water to high temperature steam before applying electrolysis.

The VHTR is the nearest term of the six reference Generation IV Roadmap reactor concepts. It is envisioned that a deliberate and focused program of research and development in support of a disciplined design and construction project could make a demonstration VHTR, with a small-scale hydrogen production system, operational by 2015. The significant advantages of high fuel burnup, passive safety, low operating and maintenance cost, and potential modular construction were evident in the Generation IV submitted concepts. The final design of the demonstration VHTR will be constrained to maintain these advantages.

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  Updated: Thursday, November 06, 2003