THTR-300

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 Site
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.^[1] 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.^[2]

On 4 June 1974, the Council of the European Communities established the Joint Undertaking "Hochtemperatur-Kernkraftwerk GmbH" (HKG).^[3]

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).^[2] 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.^[1][4]

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.^[4]

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. ^{[citation needed]} The electric conversion system produced 308 megawatts of electricity. The waste heat from the THTR-300 was exhausted using a dry cooling tower.

On May 4, 1986, fuel pebbles became lodged in the fuel feeding system due to handling errors by the control room operator. Consequently, radioactive aerosols were released to the environment via the feed system's exhaust air chimney. According to HKG scientists, the incident would not have been noticed if not for increased scrutiny due to the recency of the Chernobyl disaster. Increased levels of radioactive soil contamination led to the THTR incident being suspected as a partial culprit. The plant was shut down while the effects of the incident were assessed, and later analysis showed that the plant had not released aerosols beyond approved daily operation limits.^[5]

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.^[6]

The fuel factory in Hanau was decommissioned for security reasons, endangering the fuel fabrication chain.^{[when?][citation needed]}

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.^[7]

From 1985 to 1989, the THTR-300 registered 16,410 operation hours and generated 2,891,000 MWh. 80 incidents were logged during its 423 full-load operating day lifetime.^[8]

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.^[9]

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.^[4]

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.^[10] 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.^[11]

• Gas cooled fast reactor
• Pebble bed reactor
• Gas Turbine Modular Helium Reactor
• Anti-nuclear movement in Germany

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

• 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