Prismatic high-temperature fuel

Figure 3 briefly shows the structure, major specification and the history of the HTTR R D by JAEA. The reactor core is composed of graphite prismatic blocks. Fuels are inserted in the blocks as a shape of cylindrical graphite compacts in which tri-isotropic (TRISO)-coated fuel particles with U02 kernel are dispersed. The coolant helium gas of the HTTR is circulated at 4 MPa to an intermediate heat exchanger where high temperature heat is transferred to hydrogen production process. 

PRISMATIC-GRAPHITE-FUEL HIGH-TEMPERATURE REACTORS... 

Prismatic-Fuel Gas-Cooled High-Temperature Reactors... 

The core design and stringer approach is potentially applicable to the LS-VHTR, as shown in Fig. 4.15, with the fuel assembly shown in Fig. 4.16. The AGR fuel assembly would be replaced by an all-carbon fuel assembly capable of very high temperature operation. In the prismatic-fuel Japanese HTTR (Fig. 4.17), the fuel microspheres are contained in graphite compacts the compacts, in turn, are placed in graphite tubes. The tubes are mounted inside individual coolant channels of the prismatic fuel block. 

Several development programmes led to demonstration of high temperature gas cooled reactor features, in particular the coated fuel concept. This has been based on the Dragon project in the UK, Peach-bottom Nol and Fort St. Vrain in the US and the THTR in the Federal Republic of Germany. Currently, the HTTR, of the prismatic type, in Japan will be the first to be used for a process heat application with an outlet temperature of 850°C or above. 

CHTR - compact high temperature reactor prismatic block HTGR type fuel and lead bismuth coolant... 

CANDLE in application to high temperature gas cooled reactors with prismatic block fuel... 

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... 

Of the twenty-six concepts and designs addressed, 13 (50%) are water cooled SMRs, 6 (23%) are gas cooled SMRs-high temperature gas cooled reactors (HTGRs), 6 are sodium or lead-bismuth cooled fast reactors, and 1 is a non-conventional very high temperature reactor concept, a liquid salt cooled reactor with HTGR type prismatic fuel. 

The GT-MHR shares certain technologies and design approaches with other prismatic block or pebble bed fuel high temperature gas cooled reactor designs described in this report, e.g. GTHTR300 (Japan), PBMR-AOO (South Africa), HTR-PM (China), etc. 

There is currently a lot of interest worldwide in the development and deployment of modular high temperature gas cooled reactors. Besides in China, similar design and technology development activities are underway in France, Japan, Russia, South Africa, the USA, etc. [XVII-5-7]. Main differences between the programmes are related to fuel technology (pebble fuel versus prismatic fuel, uranium versus plutonium) and to power conversion technology (steam turbine versus gas turbine). 

The AHTR uses the typical gas cooled reactor prismatic fuel. The neutron physical characteristics (flux levels, neutron energies, etc.) are nearly identical to those of traditional high temperature gas cooled reactors. As a consequence, the fuel cycle options and characteristics are essentially identical to those of traditional gas cooled reactors as well. 

The VHTR has two typical reactor configurations, namely the pebble bed type and the prismatic block type. Although the shape of the fuel element for two configurations are different, the technical basis for both configuration is same, such as the TRISO-coated particle fuel in the graphite matrix, foil ceramic (graphite) core structure, helium coolant, and low power density, in order to achieve high outlet temperature and the retention of fission production inside the coated particle under normal operation condition and accident condition. The VHTR can support alternative fuel cycles such as U—Pu, Pu, mixed oxide (MOX), and U—thorium (Th). 

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