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The THTR-300 was a thorium cycle high-temperature
nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...
rated at 300 MW electric (THTR-300) in Hamm-Uentrop, Germany. It started operating in 1983, synchronized with the grid in 1985, operated at full power in February 1987 and was shut down on 1 September 1989. The THTR-300 served as a
prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototype ...
high-temperature reactor (HTR) to use the
TRISO Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other nuclear devices to generate energy. Oxide fuel For fission reactors, the fuel (typically based on uranium) is usually based o ...
pebble fuel produced by the AVR, an experimental pebble bed operated by VEW (Vereinigte Elektrizitätswerke Westfalen). The THTR-300 cost
The euro sign () is the currency sign used for the euro, the official currency of the eurozone. The design was presented to the public by the European Commission on 12 December 1996. It consists of a stylized letter E (or epsilon), crossed by t ...
2.05 billion and was predicted to cost an additional €425 million through December 2009 in decommissioning and other associated costs. The German state of
North Rhine Westphalia North Rhine-Westphalia or North-Rhine/Westphalia, commonly shortened to NRW, is a States of Germany, state () in Old states of Germany, Western Germany. With more than 18 million inhabitants, it is the List of German states by population, most ...
, Federal Republic of Germany, and Hochtemperatur-Kernkraftwerk
GmbH (; ) is a type of Juridical person, legal entity in German-speaking countries. It is equivalent to a (Sàrl) in the Romandy, French-speaking region of Switzerland and to a (Sagl) in the Ticino, Italian-speaking region of Switzerland. It is a ...
(HKG) financed the THTR-300’s construction.


History

On 4 June 1974, the
Council of the European Communities A council is a group of people who come together to consult, deliberate, or make decisions. A council may function as a legislature, especially at a town, city or county/shire level, but most legislative bodies at the state/provincial or nation ...
established the Joint Undertaking "Hochtemperatur-Kernkraftwerk GmbH" (HKG). 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). Heinz Riesenhuber, Federal Secretary of Research at that time, inaugurated it, and it first went critical on 13 September 1983. It started generating electricity on 9 April 1985, but did not receive permission from the atomic legal authorizing agency to feed electricity to the grid until 16 November 1985. It operated at full power in February 1987 and was shut down on 1 September 1989, after operating for less than 16,000 hours. Because the operator did not expect the decision to decommission the facility, the plant was put into "safe enclosure" status, given that this was the only technical solution for fast decommissioning, especially in consideration of the lack of a final storage facility.


Design

The THTR-300 was a
helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
-cooled high-temperature reactor with a pebble bed core consisting of approximately 670,000 spherical fuel compacts each in diameter with particles of
uranium-235 Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...
and
thorium-232 Thorium-232 () is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half life of 14.05 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its de ...
fuel embedded in a
graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...
matrix. The
pressure vessel A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...
that contained the pebbles was
prestressed concrete Prestressed concrete is a form of concrete used in construction. It is substantially prestressed (Compression (physics), compressed) during production, in a manner that strengthens it against tensile forces which will exist when in service. Post-t ...
. The THTR-300's power conversion system was similar to the Fort St. Vrain reactor in the USA, in that the reactor coolant transferred the reactor core's heat to water. The thermal output of the core was 750
megawatt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...
s; 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 The Rankine cycle is an idealized thermodynamic cycle describing the process by which certain heat engines, such as steam turbines or reciprocating steam engines, allow mechanical work to be extracted from a fluid as it moves between a heat sour ...
. 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 A cooling tower is a device that rejects waste heat to the atmosphere through the cooling of a coolant stream, usually a water stream, to a lower temperature. Cooling towers may either use the evaporation of water to remove heat and cool the ...
.


Incidents

On 4 May 1986 fuel pebbles became lodged in the fuel feeding system due to handling errors by the control room operator, specifically the manual override of the automated fuel loading mechanism, a deviation from standard operating procedures. Consequently, radioactive helium containing aerosols was released to the environment via the feed system's exhaust air chimney. The incident initially went unnoticed due to the overlap with radioactive fallout from the
Chernobyl disaster On 26 April 1986, the no. 4 reactor of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukrainian Soviet Socialist Republic, Ukrainian SSR, Soviet Union (now Ukraine), exploded. With dozens of direct casualties, it is one of only ...
, complicating attribution. An anonymous informant from the THTR-300 workforce was the first to blow the whistle on the incident, and alleged that there was a deliberate attempt to conceal the radioactive emissions from authorities and environmental groups. The reactor operators had up to this point concealed the incident from regulatory authorities, then denied any irregularities, claiming that any emissions were within permissible limits and were part of normal operations. They attributed the detected radioactivity to routine discharges or to the existing contamination from Chernobyl. Official investigations were delayed, and environmental monitoring stations eventually identified unusual levels of radioactive Protactinium-233 (²³³Pa) isotopes, inconsistent with fallout from Chernobyl. The plant had to be ordered to shut down while the effects of the incident were assessed. Later analysis showed that the plant had released radioactive aerosols, estimated at up to ''2 · 108 Bq,'' likely slightly below 180-day operation limits of 1,85 · 108 Bq, yet possibly above daily limits of 0,74 · 108 Bq. The exact amount of released material could never be determined. Control room operators, when confronted with radiation alarms, disabled aerosol measuring equipment and failed to change filters that would have allowed for exact measurements of the release, again deviating from procedures. Repeated false and misleading statements by the operator quickly eroded trust of state and federal officials, as well as the public. The backdrop of the ongoing Chernobyl crisis, where the accident was concealed, too, further undermined public perception of Germany's nuclear power plants, contributing to growing negative sentiments about nuclear energy in Germany. Beginning in late 1985, the reactor experienced difficulties with fuel elements breaking more often than anticipated. The presumptive cause of the fuel element damage was the frequent and overly-deep insertion of control rods during the commissioning process. The Nukem fuel factory in
Hanau Hanau () is a city in the Main-Kinzig-Kreis, in Hesse, Germany. It is 25 km east of Frankfurt, Frankfurt am Main and part of the Frankfurt Rhine-Main, Frankfurt Rhine-Main Metropolitan Region. Its railway Hanau Hauptbahnhof, station is a ma ...
was decommissioned in 1988 for security reasons, endangering the fuel fabrication chain. It was decided on 1 September 1989 to shut down THTR-300, which was submitted to the supervisory authority by the HKG on 26 September 1989 in accordance with the Atomic Energy Act.Der Spiegel, 8/1989 vom 20. Februar 1989, Seite 103
„Steht schlecht – Das ehrgeizige Projekt eines Hochtemperaturreaktors ist am Ende – doch Abwracken ist zu teuer.“
/ref> In the short operational life span of THTR-300 from 1985 to 1989, with only 423 full-load operating day equivalents, 80 incidents were logged. The nuclear power plant was plagued with shutdowns due to design issues, generating only 2891 GWh, far less than anticipated, never reaching the required availability of 70% (1988: 41%).Westfälischer Anzeiger 13. September 2013 ''THTR: Das Milliardengrab von Uentrop wird 30'' http://www.wa.de/lokales/hamm/uentrop/thtr-milliardengrab-hamm-uentrop-wird-jahre-3099260.html.


Decommissioning

On 1 September 1989 the THTR-300 was deactivated due to cost and the anti nuclear sentiments after Chernobyl. In August 1989, the THTR company was almost bankrupted after a long period of shut down due to broken components in the hot gas duct. The German government bailed the company out with 92 million
Mark Mark may refer to: In the Bible * Mark the Evangelist (5–68), traditionally ascribed author of the Gospel of Mark * Gospel of Mark, one of the four canonical gospels and one of the three synoptic gospels Currencies * Mark (currency), a currenc ...
. THTR-300 was in full service for 423 days. On 10 October 1991 the dry cooling tower, which at one time was the highest cooling tower in the world, was explosively dismantled and from 22 October 1993 to April 1995 the remaining fuel was unloaded and transported to the intermediate storage in
Ahaus Ahaus (; Westphalian: ''Ausen'') is a town in the district of Borken in the state of North Rhine-Westphalia, Germany. It is located near the border with the Netherlands, lying some 20 km south-east of Enschede and 15 km south from Gr ...
. The remaining facility was "safely enclosed". Dismantling is not expected to start before 2027. From 2013 to 2017, 23 Million Euro were budgeted for lighting, safeguarding and the storage of the pellets in the interim storage facility in Ahaus. As was determined in 1989, dismantling would begin after approximately 30 years in safe enclosure.


Further development

By 1990, a group of firms planned to proceed with the construction of an HTR-500, a successor of the THTR-300 with an up-rated thermal output of 1390 megawatts and electrical output of 550 megawatts. No new nuclear power plant was ever commissioned, however, as the nuclear phase-out in Germany affected research and development activities. Some high temperature reactor research eventually merged with the AVR consortium.


See also

* Gas cooled fast reactor *
Pebble bed reactor The pebble-bed reactor (PBR) is a design for a graphite- moderated, gas-cooled nuclear reactor. It is a type of very-high-temperature reactor (VHTR), one of the six classes of nuclear reactors in the Generation IV initiative. The basic desig ...
* Gas Turbine Modular Helium Reactor *
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 Wyhl protests were an example of a local community challenging the nuc ...


References


External links


General

* *
IAEA HTGR Knowledge Base


IAEA technical documents



* ttp://www.iaea.org/inisnkm/nkm/aws/htgr/abstracts/abst_iwggcr1.html Gas-cooled reactor safety and licensing aspects
THTR steam generator licensing experience as seen by the manufacturer


* ttp://www.iaea.org/inisnkm/nkm/aws/htgr/abstracts/abst_iwggcr1_17.html Aspects of water and air ingress accidents in HTRs
Safety concept of high-temperature reactors based on the experience with AVR and THTR


{{Authority control Joint undertakings of the European Union and European Atomic Energy Community Energy infrastructure completed in 1985 Former nuclear power stations in Germany Former nuclear research institutes Nuclear power stations with closed reactors Pebble bed reactors Thorium Buildings and structures in Hamm