Cooling tower of the THTR-300 (demolished in 1991)
|Commission date||November 16, 1985|
|Decommission date||April 20, 1988|
|Units decommissioned||1 x 308 MW|
The THTR-300 was a thorium high-temperature nuclear reactor 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-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 was an experimental pebble bed high-temperature reactor (HTR) used to develop the pebble fuel, the THTR-300 served as a prototype HTR to use the TRISO pebble fuel. 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 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, but 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-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 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 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.
On September 1, 1989, the THTR-300 was deactivated due to its 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 Deutsche Mark.
THTR-300 was only 423 days in full service. Just 6 months after it was connected to the power grid , May 4, 1986, fuel pebble became lodged in a fuel feed pipe to the core and some radioactive dust was released to the environment. This was just a couple of days after Chernobyl. The operators played down the incident, which caused a loss of trust in the controlling authority. The Westphalia ministery of commerce created a fact finding committee. After a couple of weeks the power plant was switched on again, but the former supporters. The fuel elements broke more often than calculated. The fuel factory in Hanau was decommissioned for security reasons. The fuel supply was diffucult before and at risk through this decision, it was decided to shut down THTR-300. 80 incidents were logged in its short lifetime. 
On October 10, 1991, the 180-metre (590 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 1992, 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. 80 incidents were logged. Despite it is not operated any more, the cost is high. For 2013 to 2017 23 Mio Euro are budgeted to lighting, guarding and the storage of the pellets in the interim storage Ahaus. The destruction cannot begin before 2022 because of radioactivity. The cost for the demolition are estimated to be hundreds of millions of euros, and it is not clear who should pay.
- Gas cooled fast reactor
- Pebble bed reactor
- Gas Turbine Modular Helium Reactor
- Anti-nuclear movement in Germany
- Decommissioning of the thorium high temperature reactor (THTR 300).
- The present state of the HTR concept based on experience gained from AVR and THTR.
- Deutscher Bundestag Drucksache 477 (PDF) (in German), 1989
- 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.
- THTR homepage (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