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The THTR-300 was a thorium
Thorium fuel cycle
The thorium fuel cycle is a nuclear fuel cycle that uses the naturally abundant isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural thorium contains only trace amounts...

 high-temperature nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

 rated at 300 MW electric (THTR-300). The German state of North Rhine Westphalia, in the Federal Republic of Germany, and Hochtemperatur-Kernkraftwerk GmbH (HKG) financed the THTR-300’s construction. Operations started on the plant in Hamm
Hamm is a city in North Rhine-Westphalia , Germany. It is located in the northeastern part of the Ruhr area. As of December 2003 its population was 180,849. The city is situated between the A1 motorway and A2 motorway...

-Uentrop, Germany in 1983, and it was shut down September 1, 1989. The THTR was synchronized to the grid for the first time in 1985 and started full power operation in February 1987. Whereas the AVR
AVR reactor
The AVR reactor was a prototype pebble bed reactor at Jülich Research Centre in West Germany. Construction began in 1960, first grid connection was in 1967 and operation ceased in 1988....

 was an experimental pebble bed high-temperature reactor (HTR) used to develop the pebble fuel, the THTR-300 served as a prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...

 HTR to use the TRISO pebble fuel. The THTR-300 cost
The euro is the official currency of the eurozone: 17 of the 27 member states of the European Union. It is also the currency used by the Institutions of the European Union. The eurozone consists of Austria, Belgium, Cyprus, Estonia, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg,...

2.05 billion and was predicted to cost an additional €425 million until December 2009 in decommissioning and other associated costs.


The electrical generation part of the THTR-300 was finished late due to ever-newer requirements and licensing procedures. It was constructed in Hamm-Uentrop from 1970 to 1983 by Hochtemperatur-Kernkraftwerk GmbH (HKG). Dr. Heinz Riesenhuber, Federal Secretary of Research at that time, inaugurated it, and it first went critical on September 13, 1983. It started generating electricity on April 9, 1985, however it did not receive permission from the atomic legal authorizing agency to feed electricity to the grid until November 16, 1985.


The THTR-300 was a helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

-cooled high-temperature reactor with a pebble bed core consisting of approximately 670,000 spherical fuel compacts each 6 centimetres (2.4 in) in diameter with particles of uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...

 and thorium-232
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

 fuel embedded in a graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...

 matrix. The pressure vessel
Pressure vessel
A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is dangerous and many fatal accidents have occurred in the history of their development and operation. Consequently, their design,...

 that contained the pebbles was prestressed concrete
Prestressed concrete
Prestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete...

 (the first time this had been used for the type of reactor, rather than the usual steel pressure vessel). The THTR-300's power conversion system was similar to the Fort St. Vrain reactor
Fort St. Vrain Generating Station
Fort Saint Vrain Generating Station is a natural gas powered electricity generating facility located near the town of Platteville in northern Colorado in the United States. It currently has a capacity of just under 1000MW and is owned and operated by Xcel Energy, the successor to the plant's...

 in the USA, in that the reactor coolant transferred the reactor core's heat to water. The thermal output of the core was 750 megawatts; heat was transferred to the helium coolant, which then transported its heat to water, which then was used to generate electricity via a Rankine cycle
Rankine cycle
The Rankine cycle is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 90% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants. It is...

. Because this system used a Rankine cycle, water could occasionally ingress into the helium circuit. The electric conversion system produced 308 megawatts of electricity. The waste heat from the THTR-300 was exhausted using a dry cooling tower
Cooling tower
Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...



On September 1, 1989 the THTR-300 was deactivated due to its ever rising cost: in August, 1989, the THTR-company became almost bankrupt after a long shut down time due to broken components in the hot gas duct. It had to be bailed out by the government with an amount of 92 million Deutschmark. Also, increased public scrutiny following both the Chernobyl accident and the THTR-300 fuel pebble event of May 4, 1986, in which a fuel pebble became lodged in a fuel feed pipe to the core and some radioactive dust was released to the environment, played some role in the decision for shut down. Further German utilities had lost any interest in pebble bed reactors. On October 10, 1991, the 180 metres (590.6 ft) high dry cooling tower, which at one time was the highest cooling tower in the world, was explosively dismantled and from October 22, 1993 to April 1995 the remaining fuel was unloaded and transported to the intermediate storage in Ahaus. The remaining facility was "safe enclosed" and dismantling will not start before 2027.

From 1985 to 1989, the THTR-300 registered 16410 operation hours and generated 2891000 MWh, according to a full-load working time of 423 days. By 1982, a group of firms planned to proceed with construction of a HTR-500, the successor of the THTR-300, but up-rated to a thermal output of 1250 megawatts and an electrical output of 500 megawatts.

See also

  • Gas cooled fast reactor
  • Pebble bed reactor
    Pebble bed reactor
    The pebble bed reactor is a graphite-moderated, gas-cooled, nuclear reactor. It is a type of very high temperature reactor , one of the six classes of nuclear reactors in the Generation IV initiative...

  • Gas Turbine Modular Helium Reactor
    Gas turbine modular helium reactor
    The Gas Turbine Modular Helium Reactor is a nuclear fission power reactor design under development by General Atomics. It is a helium cooled, graphite moderated reactor and uses TRISO fuel compacts in a prismatic core design.-Construction:...

  • Anti-nuclear movement in Germany
    Anti-nuclear movement in Germany
    The anti-nuclear movement in Germany has a long history dating back to the early 1970s, when large demonstrations prevented the construction of a nuclear plant at Wyhl. The Whyl protests were an example of a local community challenging the nuclear industry through a strategy of direct action and...


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