The High-Temperature Gas-Cooled Reactor

The core, steam generators, and helium circulators are enclosed within a reactor vessel of concrete reinforced by bonded reinforcement steel and prestressed by steel tendons. The top head houses a number of penetration channels which are used for refueling and as housings for the control rod drives. The walls of the vessel have an internal water-cooled liner of carbon steel. The liner forms a gas-tight seal and acts as the primary containment for the reactor, while the secondary containment is provided by the concrete vessel itself. All penetrations of the walls have two independent closures to maintain the principle of the double containment. 

The arrangement of the primary circuit of the reactor is illustrated in Fig. 8.5. The cooling system is divided into two loops, each of which has a six-module steam generator and two steam-driven helium circulators. The gas from all four circulators discharges into a plenum underneath the core support floor. The full flow then passes up the outside of the core to the core inlet plenum above the core. It then flows downward through the core, where it is heated to a temperature of 780°C, to the steam generators, to produce superheated and reheated steam. The steam turbines of the circulators are 

Refueling is off-load, one sixth of the fuel in the core being replaced at a time. For St. Vrain will be operated initially without recycle of the U-233 

An interesting variant of the HTGR design is the pebble-bed concept, first demonstrated in the 15-MWe AVR reactor built by Brown Boveri/Krupp at Jiilich, West Germany. The fuel is a mixture of and 

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Work has been done in developing thorium cycle converter-reactor systems. Several prototypes, including the high-temperature gas-cooled reactor (HTGR) and molten salt converter reactor experiment (MSRE), have operated. While the HTGR reactors are efficient, they are not expected to become important commercially for many years because of certain operating difficulties. Thorium is recovered commercially from the mineral monazite, which contains from 3 to 9% ThO along with rare-earth minerals. Much of the internal heat the Earth produces has been attributed to thorium and uranium. 

An important parameter in the evaluation of the safety of a reactor system is the release of fission products from the fuel. The fuel in the high-temperature gas-cooled reactor (HTGR) consists of spherical particles (U, ThC2) that are coated with a material presenting a diffusion... 

The high-temperature gas-cooled reactor (HTGR) is a thermal reactor that produces desired steam conditions. Helium is used as the coolam. Graphite, with its superior high temperature properties, is used as the moderator and structural material. The fuel is a mixture of enriched uranium and thorium in the form of carbide particles clad with ceramic coatings. 

Sakaba, N., et al. (2007), Conceptual Design of Hydrogen Production System with Thermochemical Water-splitting Iodine-Sulphur Process Utilizing Heat from the High-temperature Gas-cooled Reactor HTTR , International Journal of Hydrogen Energy, 32 (17), pp. 4160-4169. 

For nuclear hydrogen production, Japan Atomic Energy Research Institute has been developing both the high temperature gas-cooled reactor and the iodine-sulfur thermochemical process. Various other processes for nuclear hydrogen production are being proposed, evaluated or studied by many organizations in Japan. 

Table 1.3 summarizes the materials used for the principal services in pressurized-water and boiling-water reactors, the high-temperature gas-cooled reactor, fast reactors, and the molten-salt reactor, and indicates which materials are fixed in each reactor and which flow through it. 

The concept of the high-temperature gas-cooled reactor has important features such as production of electricity,... 

The High-Temperature Gas-Cooled Reactor promises still further improvements in gas temperature, power density, fuel bumup lifetime, specific power rating, and conversion ratio. Several design features of this reactor concept generally favor the use of the Th /U fuel cycle over that of the cycle. Some of the more important reasons... 

It is doubtful that the coolant temperature could be increased much more unless helium were substituted for the CO2 coolant. Future development possibilities for the AGR appear to be in the direction of the high-temperature gas-cooled reactor concept. 

The high-temperature gas-cooled reactors (HTGRs) concept evolved from early air-cooled and C02-cooled reactors. The use of helium in lieu of air or CO2 as the coolant, in combination with a graphite moderator, offered enhanced neutronic and thermal efficiencies. The combination of helium cooling and graphite moderator makes possible production of high-temperature nuclear heat, and hence the name HTGR. 

As it can be seen from both Fig. 1 and Table 1, water cooled SMRs are the most suitable candidates for a near-term deployment. The high temperature gas cooled reactors with thermal neutron spectrum follow them closely. Small PWR designs from Russia are based on the experience of the marine reactors and are said to be deployable within a very short term, once the financing for a necessary limited amount of the Research, Design Demonstration (RD D) becomes available. 

The high-temperature gas-cooled reactors have been installed in Europe. Typical multi-cavity vessels have been thoroughly analysed in this Chapter. 

Experience of the Th -U cycle was first obtained in the Indian Point boiling water reactor, where the first core, loaded in 1962, contained pellets of urania-thoria mixture. The main interest, however, has centered on its use in the high-temperature gas-cooled reactor (HTGR), and thorium has been employed as fertile material both in the prismatic fuel elements of the Dragon reactor in the United Kingdom and the Peach Bottom reactor in the United States, and in the spherical elements of the pebble-bed AVR in West Germany. There is also a possibility of adopting the thorium cycle in the... 

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