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THTR-300
Cooling tower of the THTR-300 (demolished in 1991)
Country	Germany
Coordinates	51°40′45″N 7°58′18″E / 51.67917°N 7.97167°E / 51.67917; 7.97167
Status	Decommissioned
Construction began	1971
Commission date	November 16, 1985
Decommission date	April 20, 1988
Owner	HKG
Operator	HKG
Nuclear power station
Reactor type	PBR
Power generation
Units decommissioned	1 × 308 MW
Nameplate capacity	308 MW
Capacity factor	40.1%
Annual net output	1,083 GWh
External links
Website	Official website
Commons	Related media on Commons
[edit on Wikidata]

The THTR-300 was a thorium cycle high-temperature nuclear reactor 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 September 1, 1989. The THTR-300 served as a prototype high-temperature reactor (HTR) to use the TRISO pebble fuel produced by the AVR, an experimental pebble bed operated by VEW (Vereinigte Elektrizitätswerke Westfalen). The THTR-300 cost €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, Federal Republic of Germany, and Hochtemperatur-Kernkraftwerk GmbH (HKG) financed the THTR-300’s construction.

History

On 4 June 1974, the Council of the European Communities 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 September 13, 1983. It started generating electricity on April 9, 1985, but did not receive permission from the atomic legal authorizing agency to feed electricity to the grid until November 16, 1985. It operated at full power in February 1987 and was shut down September 1, 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-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 and thorium-232 fuel embedded in a graphite matrix. The pressure vessel that contained the pebbles was prestressed concrete. 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 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. 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.

Incidents

On May 4, 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, 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 · 10 Bq, likely slightly below 180-day operation limits of 1,85 · 10 Bq, yet possibly above daily limits of 0,74 · 10 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 was decommissioned in 1988 for security reasons, endangering the fuel fabrication chain.

It was decided on September 1, 1989 to shut down THTR-300, which was submitted to the supervisory authority by the HKG on September 26, 1989 in accordance with the Atomic Energy Act.

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 %).

Decommissioning

On September 1, 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.

THTR-300 was in full service for 423 days. On October 10, 1991, the 180-metre-high (590 ft) 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 "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
• Gas Turbine Modular Helium Reactor
• Anti-nuclear movement in Germany

References

1. ^ "The present state of the HTR concept based on experience gained from AVR and THTR". Archived from the original on 4 June 2011.
2. ^ "Decommissioning of the thorium high temperature reactor (THTR 300)" (PDF).
3. 74/295/Euratom: Council Decision of 4 June 1974 on the establishment of the Joint Undertaking Hochtemperatur-Kernkraftwerk GmbH (HKG). No longer in force, Date of end of validity: 01/01/1999}}
4. ^ Dietrich, G.; Roehl, N. (31 December 1996). "Decommissioning of the thorium high-temperature reactor, THTR 300". Transactions of the American Nuclear Society. 75. OSTI 426592.
5. ^ "Funkelnde Augen – Der Hammer Reaktortyp galt als zukunftsträchtig – bis zum Störfall Anfang Mai" [Sparkling eyes – The Hammer reactor type was considered to have a promising future – until the accident in early May.]. Der Spiegel. No. 24/1986. 9 June 1986. p. 28. Archived from the original on 31 October 2022. Retrieved 24 November 2024.
6. ^ Nordrhein-Westfalen/Minister für Wirtschaft, Mittelstand und Technologie (7 September 2006) . "Information zur Emission radioaktiver Aerosole aus dem THTR 300 in Hamm-Uentrop am 4. Mai 1986, Vorlage 10/561" [Information on the emission of radioactive aerosols from the THTR 300 in Hamm-Uentrop on May 4, 1986, parliamentary submission 10/561] (PDF). parliamentary database of the State Parliament of North Rhine-Westphalia, Germany (Parliamentary submission) (in German). Archived (PDF) from the original on 27 February 2015. Retrieved 30 November 2024.
7. ^ 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.
8. Bäumer, R.; Kalinowski, I.; Röhler, E.; Schöning, J.; Wachholz, W. (2 July 1990). "Construction and operating experience with the 300-MW THTR nuclear power plant". Nuclear Engineering and Design. 121 (2): 155–166. doi:10.1016/0029-5493(90)90100-C. ISSN 0029-5493.
9. 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.“
10. Atomwirtschaft, Mai 1989, S. 259
11. Deutscher Bundestag Drucksache 477 (PDF) (PDF) (in German), 1989
12. Theymann, Walter (1 August 1992). "Status and prospects of the HTR 500 based on the THTR 300 operation experience and recent R&D-work". Nuclear Engineering and Design. 136 (1): 127–133. doi:10.1016/0029-5493(92)90120-K. ISSN 0029-5493.
13. Allelein, H. -J.; Verfondern, K. (1 June 2018). "Major milestones of HTR development in Germany and still open research issues". Annals of Nuclear Energy. 116: 114–127. doi:10.1016/j.anucene.2018.02.012. ISSN 0306-4549.

External links

General

• Official website (in German)
• Cooling Tower of the Schmehausen Nuclear Plant at Structurae
• IAEA HTGR Knowledge Base

IAEA technical documents

• The THTR steam generator: design, manufacture and installation
• Gas-cooled reactor safety and licensing aspects
• THTR steam generator licensing experience as seen by the manufacturer
• Accident analysis and accident control for the THTR - 300 power plant
• Aspects of water and air ingress accidents in HTRs
• Safety concept of high-temperature reactors based on the experience with AVR and THTR
• The behaviour of spherical HTR fuel elements under accident conditions

• 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