Page 191 - Managing Global Warming

Current and future nuclear power reactors and plants 153

Fig. 4.30 Very-high-temperature reactor (VHTR): Helium-gas-cooled, graphite-moderated,
thermal-neutron-spectrum reactor with core outlet temperature 900–1000°C (shown with
hydrogen cogeneration).
Courtesy of Generation IV International Forum.

temperature >900°C, and a goal of 1000°C, sufficient to support high-temperature
processes such as production of hydrogen through thermochemical processes. The
thermal power of the reactor is set at a level that allows passive decay-heat removal,
currently estimated to be about 600MW th . The VHTR is useful for cogeneration of
electricity and hydrogen, as well as for other process-heat applications, related to
the chemical, oil, and iron industries. It is able to produce hydrogen from water by
using thermochemical, electrochemical, or hybrid processes with reduced emission
of CO 2 gases. At first, a once-through low-enriched uranium (LEU) (<20% U 235 ) fuel
cycle will be adopted, but a closed fuel cycle will be assessed, as well as potential
symbiotic fuel cycles with other types of reactors (especially, light-water reactors
(LWRs)) for waste-reduction purposes. The system is expected to be available for
commercial deployment by 2020.
The technical basis for VHTR is the tri-isotropic (TRISO)-coated particle fuel. The
VHTR has potential for inherent safety, high thermal efficiency, process-heat-
application capability, low operation and maintenance costs, and modular
construction.
In general, the reactor core of the VHTR can be a prismatic block core such as the
Japanese high-temperature test reactor (HTTR), or a pebble-bed core such as the