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50-718: 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

100-550: A neutron (whether in a fast reactor or thermal reactor ) to become Th . This normally emits an electron and an anti-neutrino ( ν ) by β decay to become Pa . This then emits another electron and anti-neutrino by a second β decay to become U , the fuel: Nuclear fission produces radioactive fission products which can have half-lives from days to greater than 200,000 years . According to some toxicity studies,

150-454: A radiological hazard that necessitate the use of remote handling of separated uranium and aid in the passive detection of such materials. The long-term (on the order of roughly 10 to 10  years ) radiological hazard of conventional uranium-based used nuclear fuel is dominated by plutonium and other minor actinides , after which long-lived fission products become significant contributors again. A single neutron capture in U

200-424: A fertile material thorium is similar to U , the major part of natural and depleted uranium. The thermal neutron absorption cross section (σ a ) and resonance integral (average of neutron cross sections over intermediate neutron energies) for Th are about three and one third times those of the respective values for U . The primary physical advantage of thorium fuel

250-457: A long-term radiological impact, especially Pa and U . On a closed cycle, U and Pa can be reprocessed. Pa is also considered an excellent burnable poison absorber in light water reactors. Another challenge associated with the thorium fuel cycle is the comparatively long interval over which Th breeds to U . The half-life of Pa

300-408: A long-time promoter of thorium fuel cycle and particularly liquid fluoride thorium reactors (LFTRs). He first researched thorium reactors while working at NASA , while evaluating power plant designs suitable for lunar colonies. In 2006 Sorensen started "energyfromthorium.com" to promote and make information available about this technology. A 2011 MIT study concluded that although there is little in

350-666: A relatively short half-life ( 68.9 years ), and some decay products emit high energy gamma radiation , such as Rn , Bi and particularly Tl . The full decay chain , along with half-lives and relevant gamma energies, is: U decays to Th where it joins the decay chain of Th Thorium-cycle fuels produce hard gamma emissions , which damage electronics, limiting their use in bombs. U cannot be chemically separated from U from used nuclear fuel ; however, chemical separation of thorium from uranium removes

400-433: A traditional light water reactor though not in a molten salt reactor . Concerns about the limits of worldwide uranium resources motivated initial interest in the thorium fuel cycle. It was envisioned that as uranium reserves were depleted, thorium would supplement uranium as a fertile material. However, for most countries uranium was relatively abundant and research in thorium fuel cycles waned. A notable exception

450-444: Is about 1:12 – which is better than the corresponding capture vs. fission ratios of U (about 1:6), or Pu or Pu (both about 1:3). The result is less transuranic waste than in a reactor using the uranium-plutonium fuel cycle. U , like most actinides with an even number of neutrons, is not fissile, but neutron capture produces fissile U . If

500-474: Is about 27 days, which is an order of magnitude longer than the half-life of Np . As a result, substantial Pa develops in thorium-based fuels. Pa is a significant neutron absorber and, although it eventually breeds into fissile U , this requires two more neutron absorptions, which degrades neutron economy and increases the likelihood of transuranic production. Alternatively, if solid thorium

550-689: Is estimated to be about three to four times more abundant than uranium in Earth's crust, although present knowledge of reserves is limited. Current demand for thorium has been satisfied as a by-product of rare-earth extraction from monazite sands. Notably, there is very little thorium dissolved in seawater, so seawater extraction is not viable, as it is with uranium. Using breeder reactors, known thorium and uranium resources can both generate world-scale energy for thousands of years. Thorium-based fuels also display favorable physical and chemical properties that improve reactor and repository performance. Compared to

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600-807: Is hard to validate the exact benefits. Thorium fuels have fueled several different reactor types, including light water reactors , heavy water reactors , high temperature gas reactors , sodium-cooled fast reactors , and molten salt reactors . From IAEA TECDOC-1450 "Thorium Fuel Cycle – Potential Benefits and Challenges", Table 1: Thorium utilization in different experimental and power reactors. Additionally from Energy Information Administration, "Spent Nuclear Fuel Discharges from U. S. Reactors", Table B4: Dresden 1 Assembly Class. [REDACTED] Nuclear technology portal [REDACTED] Energy portal Nukem Energy Nukem GmbH , together with its subsidiary Nukem Inc., markets nuclear fuel components and speciality products utilities worldwide. Since

650-407: Is mostly focused on transuranic waste. Furthermore, the cross section of some fission products is relatively low and others - such as caesium - are present as a mixture of stable, short lived and long lived isotopes in nuclear waste, making transmutation dependent on expensive isotope separation . In a reactor, when a neutron hits a fissile atom (such as certain isotopes of uranium), it either splits

700-571: Is necessary to achieve a favorable neutron economy . Although thorium dioxide performed well at burnups of 170,000 MWd/t and 150,000 MWd/t at Fort St. Vrain Generating Station and AVR respectively, challenges complicate achieving this in light water reactors (LWR), which compose the vast majority of existing power reactors. In a once-through thorium fuel cycle, thorium-based fuels produce far less long-lived transuranics than uranium-based fuels, some long-lived actinide products constitute

750-785: Is only under development. Although the presence of U complicates matters, there are public documents showing that U has been used once in a nuclear weapon test. The United States tested a composite U -plutonium bomb core in the MET (Military Effects Test) blast during Operation Teapot in 1955, though with much lower yield than expected. Advocates for liquid core and molten salt reactors such as LFTRs claim that these technologies negate thorium's disadvantages present in solid fuelled reactors. As only two liquid-core fluoride salt reactors have been built (the ORNL ARE and MSRE ) and neither have used thorium, it

800-432: Is relatively low, making this rather difficult and possibly uneconomic. U is also formed in this process, via ( n ,2 n ) reactions between fast neutrons and U , Pa , and Th : Unlike most even numbered heavy isotopes, U is also a fissile fuel fissioning just over half the time when it absorbs a thermal neutron. U has

850-439: Is sufficient to produce transuranic elements , whereas five captures are generally necessary to do so from Th . 98–99% of thorium-cycle fuel nuclei would fission at either U or U , so fewer long-lived transuranics are produced. Because of this, thorium is a potentially attractive alternative to uranium in mixed oxide (MOX) fuels to minimize the generation of transuranics and maximize

900-441: Is that it uniquely makes possible a breeder reactor that runs with slow neutrons , otherwise known as a thermal breeder reactor . These reactors are often considered simpler than the more traditional fast-neutron breeders. Although the thermal neutron fission cross section (σ f ) of the resulting U is comparable to U and Pu , it has a much lower capture cross section (σ γ ) than

950-485: Is used in a closed fuel cycle in which U is recycled , remote handling is necessary for fuel fabrication because of the high radiation levels resulting from the decay products of U . This is also true of recycled thorium because of the presence of Th , which is part of the U decay sequence. Further, unlike proven uranium fuel recycling technology (e.g. PUREX ), recycling technology for thorium (e.g. THOREX)

1000-474: The Pa (with a half-life of 3.27 × 10  years ) formed via ( n ,2 n ) reactions with Th (yielding Th that decays to Pa ), while not a transuranic waste, is a major contributor to the long-term radiotoxicity of spent nuclear fuel. While Pa can in principle be converted back to Th by neutron absorption , its neutron absorption cross section

1050-493: 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

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1100-569: The 1960s, the Molten-Salt Reactor Experiment used U as the fissile fuel in an experiment to demonstrate a part of the Molten Salt Breeder Reactor that was designed to operate on the thorium fuel cycle. Molten salt reactor (MSR) experiments assessed thorium's feasibility, using thorium(IV) fluoride dissolved in a molten salt fluid that eliminated the need to fabricate fuel elements. The MSR program

1150-633: The 1970s, Nukem has transitioned from playing a modest role in uranium brokerage to becoming one of the world's largest intermediaries in the international nuclear fuel market. Nukem was established in 1960 by Degussa , Rio Tinto and Mallinckrodt . In 1965, RWE acquired 25% of shares. Effective April 1, 2006, the private equity firm Advent International has taken over Nukem. In 2007, Nukem sold its subsidiaries NUKEM Ltd. to Freyssinet SAS , NUKEM Corp. to EnergySolutions , NIS Ingenieure and Assistance Nucleaire S.A. to Siempelkamp. On 14 December 2009, Nukem sold its subsidiary Nukem Technologies, which

1200-509: 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

1250-420: The amount of nuclear waste and the duration during which it would have to be stored (whether in a deep geological repository or elsewhere). However, while the principal feasibility of some of those reactions has been demonstrated at laboratory scale, there is, as of 2024, no large scale deliberate transmutation of fission products anywhere in the world, and the upcoming MYRRHA research project into transmutation

1300-450: 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

1350-467: The decay product Th and the radiation from the rest of the decay chain, which gradually build up as Th reaccumulates. The contamination could also be avoided by using a molten-salt breeder reactor and separating the Pa before it decays into U . The hard gamma emissions also create a radiological hazard which requires remote handling during reprocessing. As

1400-404: The destruction of plutonium. There are several challenges to the application of thorium as a nuclear fuel, particularly for solid fuel reactors: In contrast to uranium, naturally occurring thorium is effectively mononuclidic and contains no fissile isotopes; fissile material, generally U , U or plutonium, must be added to achieve criticality . This, along with

1450-503: 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

1500-541: The fissile isotope fails to fission on neutron capture, it produces U , Np , Pu , and eventually fissile Pu and heavier isotopes of plutonium . The Np can be removed and stored as waste or retained and transmuted to plutonium, where more of it fissions, while the remainder becomes Pu , then americium and curium , which in turn can be removed as waste or returned to reactors for further transmutation and fission. However,

1550-467: 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 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

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1600-428: The high sintering temperature necessary to make thorium-dioxide fuel, complicates fuel fabrication. Oak Ridge National Laboratory experimented with thorium tetrafluoride as fuel in a molten salt reactor from 1964 to 1969, which was expected to be easier to process and separate from contaminants that slow or stop the chain reaction. In an open fuel cycle (i.e. utilizing U in situ), higher burnup

1650-536: 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

1700-434: The lack of a final storage facility. 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

1750-481: The latter two fissile isotopes, providing fewer non-fissile neutron absorptions and improved neutron economy . The ratio of neutrons released per neutron absorbed (η) in U is greater than two over a wide range of energies, including the thermal spectrum. A breeding reactor in the uranium–plutonium cycle needs to use fast neutrons, because in the thermal spectrum one neutron absorbed by Pu on average leads to less than two neutrons. Thorium

1800-573: The nuclear phase-out in Germany affected research and development activities. Some high temperature reactor research eventually merged with the AVR consortium. Thorium fuel cycle The thorium fuel cycle has several potential advantages over a uranium fuel cycle , including thorium's greater abundance , superior physical and nuclear properties, reduced plutonium and actinide production, and better resistance to nuclear weapons proliferation when used in

1850-410: The nucleus or is captured and transmutes the atom. In the case of U , the transmutations tend to produce useful nuclear fuels rather than transuranic waste. When U absorbs a neutron, it either fissions or becomes U . The chance of fissioning on absorption of a thermal neutron is about 92%; the capture-to-fission ratio of U , therefore,

1900-732: The predominant reactor fuel, uranium dioxide ( UO 2 ), thorium dioxide ( ThO 2 ) has a higher melting point , higher thermal conductivity , and lower coefficient of thermal expansion . Thorium dioxide also exhibits greater chemical stability and, unlike uranium dioxide, does not further oxidize . Because the U produced in thorium fuels is significantly contaminated with U in proposed power reactor designs, thorium-based used nuclear fuel possesses inherent proliferation resistance. U cannot be chemically separated from U and has several decay products that emit high-energy gamma radiation . These high-energy photons are

1950-477: 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

2000-440: 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,

2050-481: The required availability of 70% (1988: 41 %). 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,

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2100-481: 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. 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

2150-543: The thorium cycle can fully recycle actinide wastes and only emit fission product wastes, and after a few hundred years, the waste from a thorium reactor can be less toxic than the uranium ore that would have been used to produce low enriched uranium fuel for a light water reactor of the same power. Other studies assume some actinide losses and find that actinide wastes dominate thorium cycle waste radioactivity at some future periods. Some fission products have been proposed for nuclear transmutation , which would further reduce

2200-423: The way of barriers to a thorium fuel cycle, with current or near term light-water reactor designs there is also little incentive for any significant market penetration to occur. As such they conclude there is little chance of thorium cycles replacing conventional uranium cycles in the current nuclear power market, despite the potential benefits. In the thorium cycle, fuel is formed when Th captures

2250-478: Was India's three-stage nuclear power programme . In the twenty-first century thorium's claimed potential for improving proliferation resistance and waste characteristics led to renewed interest in the thorium fuel cycle. While thorium is more abundant in the continental crust than uranium and easily extracted from monazite as a side product of rare earth element mining, it is much less abundant in seawater than uranium. At Oak Ridge National Laboratory in

2300-578: Was defunded in 1976 after its patron Alvin Weinberg was fired. In 1993, Carlo Rubbia proposed the concept of an energy amplifier or "accelerator driven system" (ADS), which he saw as a novel and safe way to produce nuclear energy that exploited existing accelerator technologies. Rubbia's proposal offered the potential to incinerate high-activity nuclear waste and produce energy from natural thorium and depleted uranium . Kirk Sorensen, former NASA scientist and Chief Technologist at Flibe Energy, has been

2350-675: 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. On 4 June 1974, the Council of the European Communities established the Joint Undertaking "Hochtemperatur-Kernkraftwerk GmbH" (HKG). The electrical generation part of

2400-547: 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

2450-511: 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

2500-509: 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

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