High-temperature reactor-pebble bed

FIGU RE 21.20 Fuel spheres used In a hIgh-temperature pebble-bed reactor. 

A Figure 21.20 Fuel spheres used in a high-temperature pebble-bed reactor. The image on the right is an optical microscope image of a fuel particle. 

In a high-temperature pebble-bed reactor, the fuel elements are spheres ( pebbles ) roughly the size of an orange (A Figure 21.20). The spheres are made of graphite, which acts as the moderator, and thousands of tiny fuel particles are embedded in the interior of each sphere. Each fuel particle is a kernel of fissionable material, typically... 

High temperature rectors were very successful in Germany as pebble bed reactors (PBR s) with the AVR-reactor in Jiilich over 20 years, 50 MW l/h, and with the THTR 300 in Hamm-Ueontrop with 300 MW, which was tested electrically for 3 years. 

Two kinds of indirect GT-ST cycle are investigated based on Siemens 200 MW pebble-bed modular high temperature gas cooled reactor(HTR-Module). Fig. I shows the HTR-Module and its primary loop. 

A review of work in the United States on gas cooling for reactors is given by Troost et al. (19). Heat-transfer correlations have been developed for different core configurations, such as cores with cylindrical fuel elements or pebble bed reactors. In high-temperature, gas-cooled reactors composed of an assembly of cylindrical fuel elements cooled on the out-... 

The typical HTGR fuels are the pebble-bed type, which is a graphite sphere, and the block type fuel i.e., a graphite block into which coated particles are inserted (Saito et al. 1994). The former is generally suitable for high temperature operation because the fuel spheres circulate slowly in the reactor and each fuel sphere is exposed to high temperature in the reactor for... 

A second type of GCR used the pebble bed concept with helium as a coolant. The uranium and thorium fuel was imbedded in graphite spheres and cooled with helium. The high temperature thorium fueled reactor (THTR) operated between 1985 and 1989 in Germany. It produced 760 MWt and 307 MWe. The thorium in the fuel pellets was used to breed Two GCR power plants have been operated in the United States. The first was Peach Bottom Unit 1, which provided 40 MWe. The second was the Fort St. Vrain reactor, which provided 330 MWe. 

No operations with fuel are performed during the entire reactor lifetime therefore, there is no storage capacity for fresh or spent fuel elements on the site. Different from pebble bed high temperature gas cooled reactors (HTGRs) and previous high temperature molten salt cooled reactors with HTGR type fuel (abbreviated as VTRS in Russian), the MARS concept incorporates no pebble transport. 

Figure 11.10 Design of a spherical fuel element ( pebble ) of a very high-temperature (VHTR) gas-cooled pebble bed reactor (PBR).

After more than 21 years of operation, the 15 MWe AVR experimental nuclear power plant with pebble bed high temperature gas-cooled reactor was shut down in 1988. Safestore decommissioning began in 1994. In order to completely dismantle the plant, a concept for Continued dismantling was developed according to which the plant could be dismantled in a step-wise procedure. After each step, there is the possibility to transform the plant into a new state of safe enclosure. 

The presentations also outlined certain enabling technologies that may be common for several different reactor lines. For example, coated particle or pebble bed type fuel is considered for use not only in high temperature gas cooled reactors, such as PBMR and HTR-PM, but also in several innovative water cooled, molten salt cooled, and even lead-bismuth cooled SMRs, such as PFPWR50 (Japan), VKR-MT (Russia), perhaps FBNR (Brazil), MARS (Russia), and CHTR (India). Some projections for the advanced high temperature structural materials of... 

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... 

The primary system will facilitate the direct movement of heat energy from the pebble bed reactor to the power conversion system by the use of high pressure, high temperature helium. This will be a first-of-a-kind NPP application. There will not be an intervening coolant such as steam. 

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. 

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