Fusion energy

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View of the plasma in the MAST test facility

In the context of research policy, fusion energy refers to the large-scale use of thermonuclear nuclear fusion to generate electricity . The prospect of a virtually inexhaustible source of energy without the risk of catastrophic accidents and without the need for disposal of long-lived radioactive waste is the motivation for long-term, international research activities.

The most complex and expensive project at the moment is the international research reactor ITER . With the reactor, which has been built in the south of France since 2007, it will be possible to investigate whether an energy surplus - i.e. H. more fusion power is generated than is required in terms of energy supply - which is technically feasible. The next step could be the DEMO project , with which it should be shown that electricity generation by nuclear fusion is in principle possible and that a sufficiently large amount of the fuel tritium can be generated in the power plant itself. If this research work should be successful, plants of economic size with an electrical output of 1000 to 1500  MW could be built in the last quarter of the 21st century according to current knowledge.

Technical feasibility

The most technically advanced concept for the permanent containment of a thermonuclear reacting plasma is that of the tokamak . Plasma instabilities of various types represent a difficulty. The mechanisms for their suppression are being intensively researched. Due to the inductively generated plasma flow, a tokamak in its original version can only be operated in a pulsed manner, which would be technically very disadvantageous; Research is also being carried out into additional techniques for the permanent maintenance of electricity ( current drive ). With the stellarator concept, fewer inherent stability problems are expected, and steady continuous operation is basically possible here. However, the stellarator concept is less developed in practice. Whether the first fusion power plant ( DEMO ) should be built as a tokamak or a stellarator has not yet been decided (2019).

The so-called triple product is an important measure for the progress of fusion research . It has to come close to a value given by the Lawson criterion for a reactor to be economical (see fusion by means of magnetic confinement ). Since the beginning of fusion research in the 1960s, the value of the triple product has increased by around 10,000 times, so that at the beginning of 2016 you are only a factor between seven and ten away from the ignition. In 1997, JET briefly (for less than 200 milliseconds) achieved 16 MW fusion power with 24 MW injected heating power. The larger tokamak called ITER is supposed to demonstrate 500 MW fusion power at 50 MW heating power for 1000 seconds. This shows the technical feasibility of a Q-factor (defined as the ratio of fusion power to heating power) of ten.

For decades, prognoses about power-supplying reactors have been around 30 to 50 years in the future. Some critics mockingly refer to this period as the “fusion constant”. There are several reasons for the fact that the forecasts were too optimistic: the process of merging two atomic nuclei, which is simple in itself, is integrated into a complex plasma-physical environment that must first be understood and mastered. In the practical implementation, new challenges of a technological and material nature arose, for example temperatures of over 100 million degrees had to be reached. Financing, construction and operation of the large-scale plants are often delayed for political reasons, especially in view of the costs of the ITER project.

At the end of April 2016, the Max Planck Institute for Plasma Physics announced that previous experiments and further investigations had shown that continuous operation of a tokamak is technically feasible. This means that the “conditions for ITER and DEMO are almost fulfilled”.

economics

Even if fusion power plants should be technically feasible, this does not mean that they can also be operated economically. In the status report of the German Bundestag from 2002 it says: “Overall, it is therefore controversial whether demo will be followed by fusion power plants that can be operated economically. It is possible that initial difficulties will require further state support (Heindler 2001). "

The current chairman of the German Advisory Council on Global Change (WBGU) , Hans Joachim Schellnhuber , who is also director of the Potsdam Institute for Climate Impact Research , criticized the high costs of nuclear fusion research in 2015 in view of the potential of solar energy:

“While we have been working decade after decade on developing an incredibly expensive fusion reactor, we are already blessed with one that works perfectly well and is free to all of us: the Sun”

"While we have worked decade after decade to develop an incredibly expensive fusion reactor, we are already blessed with one that works flawlessly and is free for all of us: the sun"

- Hans-Joachim Schellnhuber : common-ground

EUROfusion , the umbrella organization for European nuclear fusion research, is based on the following scenario: Provided that fossil fuels are pushed back because of their harmful effects on the climate and that nuclear fusion is therefore economically competitive, large-scale use of the new technology could, based on current knowledge, be from the middle of the 21st century respectively. Some therefore doubt that fusion energy can play a role in the energy transition. Among other things, this late availability led the WBGU to the conclusion in 2003 that it was not justifiable to have energy concepts for the future "even only partially based on nuclear fusion" given the current status.

Effects on the structure of the energy supply

The demonstration power plant DEMO is expected to produce some 100 MW of electrical power for the first time. However, it will still be too small for commercial operation.

Because the construction and financing costs represent the major part of the total expenditure in the case of fusion power plants , they could be used in particular as base load power plants . In 2002, with reference to a source from 2001, a report to the Bundestag stated: “For base load power plants, reliability is a decisive parameter. Frequent unforeseen interruptions or long downtimes for maintenance and repair would make fusion power plants unattractive. The power availability of a fusion power plant of 75% assumed today (Bradshaw 2001) is comparatively low compared to other large power plants, some of which reach over 95%. "

Environmental and safety aspects

Fusion power plants would and would have replaced those based on nuclear fission and fossil fuels

  • in contrast to conventional power plants based on coal, oil or gas
    • no emission of exhaust gases, especially greenhouse gases such as CO 2 ;
    • no problems with the fuel supply for a very long time, while fossil fuels are likely to become too expensive;
    • negligible costs of the fuels, the extraction of which is not a problem with regard to environmental risks either.
  • in contrast to nuclear fission reactors
    • no reaction that can become supercritical or run thermally . If the magnetic field cannot hold the plasma together, it cools down on the wall and the fusion reaction stops.
    • no disposal problems due to very long-lived radioactive material.
    • Transport of radioactive fuel is only necessary for a one-off initial supply with a tritium supply of around 1 kg. The starting materials lithium and deuterium are not radioactive.
  • similar to nuclear fission reactors
    • considerable neutron activation of structural materials. The total radioactive inventory of the plant would be comparable during operation with that of a fission reactor power plant of the same capacity. However, very long-lived waste materials could be avoided.
    • Plant components that would be exposed to such strong neutron radiation that they would have to be regularly replaced and temporarily stored. In conventional nuclear reactors, in particular the fuel element casings in which the uranium fuel is located are exchanged together with the fuel; in the case of fusion reactors, these would in particular be parts of the divertor and the blanket. However, due to the complicated geometry, replacement is more time-consuming than replacing fuel elements in a nuclear reactor.
    • Contamination that would make maintenance work even more difficult: While gaseous tritium is oxidized to water, pumped out and collected in cold traps, the contamination of wall material is a major problem. Tritium is ion-implanted or deposited again with eroded carbon. This tritium is not easy to collect, but it is also not securely bound.
    • Mobile radioactive inventory that could be released in the event of a disaster: The radioactive tritium hatched in the blanket is extracted within the system and used again. The supply for a one-week operation would be a few kilograms with a 1 GW system and an activity of 10 18  Bq . That is roughly the activity of the radioactive iodine released in the Chernobyl nuclear disaster , but only a small fraction of the more than 600 kg of tritium that was released into the atmosphere through nuclear weapons tests in the past century .

Deuterium-tritium fusion reactors would therefore not be free from radioactivity problems, but would be an advance over conventional nuclear fission reactors in terms of safety and environmental compatibility .

Nuclear Proliferation Risks

Nuclear fusion technology has only a limited overlap with nuclear weapons technology . However, nuclear fusion can theoretically produce material for nuclear weapons and thus increase the risk of nuclear weapons spreading .

Modification of a commercial fusion reactor is seen as the fastest way to produce weapons-grade material. In contrast to a power plant based on nuclear fission, a pure fusion reactor does not contain any material that can be used for nuclear weapons without conversion.

Large amounts of tritium are produced in fusion reactors and an unauthorized diversion of a small amount, but sufficient for military use, is considered to be difficult to control. Just a few grams of a deuterium-tritium mixture can significantly increase the energy released by an atom bomb and thus its destructive power. The method is known as the fusion booster . Tritium is also produced as a radioactive waste product in conventional nuclear reactors, especially in heavy water reactors , but is usually neither separated nor concentrated to form a pure substance. The danger of proliferation comes from the tritium itself as well as from knowing the details of its production.

If 6 Li enriched in the breeding jacket of a fusion reactor is used, corresponding large-scale facilities for lithium enrichment must be built. Finally, direct proliferation is also conceivable with enriched 6 Li. Hydrogen bombs achieve a higher explosive power with enriched 6 Li than with natural lithium.

The production of nuclear weapons- grade plutonium or uranium is in principle possible using the hard neutron radiation emitted by the fusion reactor, for example by transmutation from 238 U to 239 Pu, or 232 Th to 233 U.

A study by RJ Goldston, A. Glaser and AF Ross examined the risks of nuclear proliferation through fusion reactors and analyzed various scenarios for the production of weapons-grade plutonium or uranium. Due to the significantly higher energy consumption, the associated heat release and a conspicuous construction, the use of even a small fusion reactor compared to gas centrifuges was rated as very implausible in this study .

In regular operation for civil energy production, there would be no breeding or fissile material in pure fusion power plants. Without shielding, these materials can be detected very well via the gamma radiation emitted by them with characteristic energy. This would be a strong indication of military use of the facility. Some of the possible technical modifications, which introduce breeding material in very low concentration into the cooling substance and extract it again, would probably not be hidden from inspectors because of their dimensions. With this method, a subsequent processing of the material would also be extremely time-consuming. The installation of a module of the brood mantle, which, for example, would be equipped with unauthorized uranium oxide, is described as the most realistic risk of weapons spreading. The study considers it necessary that by checking the delivered components such possibilities are prevented, otherwise plutonium could be produced for several nuclear weapons annually.

Even without the need for covert action, it would take two months to start production and at least another week to get a significant amount for weapons production. This period of time is long enough to discover a military use and to respond with diplomatic means or with the military destruction of parts of the facility. In contrast to a nuclear power plant, only secondary structures would have to be destroyed in order to paralyze the entire production process; if the intrinsic safety of the fusion power plants were added, the risk of radioactive contamination would be low.

Another study comes to the conclusion that large fusion reactors could produce up to a few hundred kilograms of plutonium annually with great suitability for weapons, with comparably low requirements for the starting material. The authors point out that intrinsic security features that make military use difficult may only be implemented at the current, early research stage.

Web links

literature

  • TC Hender et al .: Fusion Technology
  • Energy Research Center of the Netherlands : Long Term Energy Scenarios
  • T. Hamacher: Fusion, Engineering and Design
  • JG Delene, J. Sheffield, KA Williams, RL Reid, S. Hadley: An Assessment of the Economics of Future Electric Power Generation Options
  • Institute for Management (IIM), Max Planck Institute for Plasma Physics (IPP), Netherlands Energy Research Foundation (ECN): Longterm Energy Scenarios for India
  • Alexander M. Bradshaw (IPP), Reinhard Maschuw (FZK), Gerd Eisenbeiß (FJZ): Nuclear fusion (brochure of the Helmholtz Association )

Notes and individual references

  1. "deuterium can be easily extracted at a very low cost", "enough [...] for 2 billion years" (p. 16), "20,000 years of inexpensive Li6 available" (p. 17) In: Jeffrey P. Freidberg: Plasma Physics And Fusion Energy. 2007.
  2. Jeffrey P. Freidberg: Plasma Physics And Fusion Energy. 2007, p. 17.
  3. ^ Weston M. Stacey: Fusion. An Introduction to the Physics and Technology of Magnetic Confinement Fusion. 2010, pp. 151-154; radioactive structural material […] storage time required […] 100 years.
  4. AM Bradshaw: The Long Road to ITER , PDF. Max Planck Institute for Plasma Physics (IPP), October 28, 2005.
  5. 50 years of research for the energy of the future (PDF; 5.8 MB). Max Planck Institute for Plasma Physics (IPP), 2010. Accessed July 3, 2013. ISBN 978-3-00-031750-7 .
  6. EURO fusion .org: Fusion Technology - From experiment to power plant ( Memento of the original from April 9, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot / www.euro-fusion.org
  7. a b Fusion Electricity - A roadmap to the realization of fusion energy . Euro-Fusion.org. 2012. Retrieved December 24, 2016.
  8. a b EURO fusion .org: The Road to Fusion Electricity . Retrieved December 24, 2016.
  9. Ulf von Rauchhaupt: Sonnenfeuer am Boden - After ten years of planning, only the economy version of the international nuclear fusion reactor Iter remains , DIE ZEIT, 1999.
  10. http://www.ipp.mpg.de/de/aktuelles/presse/pi/2016/04_16
  11. Armin Grunwald, Reinhard Grünwald, Dagmar Oertel, Herbert Paschen: Nuclear fusion. Status report (PDF; 396 kB). Work report of the Office for Technology Assessment at the German Bundestag, March 2002, p. 49.
  12. https://www.pik-potsdam.de/images/common-ground
  13. Umweltinstitut München, nuclear fusion - expensive and superfluous ( Memento of the original from April 6, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , July 2013 @1@ 2Template: Webachiv / IABot / www.umweltinstitut.org
  14. Anatol Hug: Nuclear Fusion: You Must Know That . Swiss Radio and Television - Knowledge, March 23, 2015.
  15. Scientific Advisory Council of the Federal Government on Global Change : World in Transition - Energy Transition towards Sustainability . Berlin Heidelberg 2003, p. 53
  16. Demonstration power plant DEMO (Max Planck Institute for Plasma Physics)
  17. Armin Grunwald, Reinhard Grünwald, Dagmar Oertel, Herbert Paschen: Nuclear fusion. Status report (PDF; 396 kB). Work report of the Office for Technology Assessment at the German Bundestag, March 2002, pp. 48–49. Retrieved June 17, 2014.
  18. ITER & Safety Archivlink ( Memento of November 12, 2009 in the Internet Archive ), ITER Organization (English)
  19. ITER Fusion Fuels , ITER Organization (English)
  20. Joachim Roth et al .: Tritium inventory in ITER plasma-facing materials and tritium removal procedures . Plasma Phys. Control. Fusion 50, 2008, 103001, doi : 10.1088 / 0741-3335 / 50/10/103001 .
  21. A. Fiege (Ed.), Tritium. Report KfK-5055, Nuclear Research Center Karlsruhe, 1992, pp. 54-57 ISSN  0303-4003 .
  22. a b c Matthias Englert, Giorgio Franceschini, Wolfgang Liebert: Strong Neutron Sources - How to cope with weapon material production capabilities of fusion and spallation neutron sources? 7th INMM / Esarda Workshop, Aix ‐ en ‐ Provence, 2011 (PDF; 2.3 MB).
  23. ^ Martin Kalinowski: International control of tritium for nuclear nonproliferation and disarmament . CRC Press, 2004, ISBN 0-415-31615-4 , pp. 34 .
  24. ^ A b c d R. J. Goldston, A. Glaser, AF Ross: "Proliferation Risks of Fusion Energy: Clandestine Production, Covert Production, and Breakout" (PDF; 2.3 MB) 9th IAEA Technical Meeting on Fusion Power Plant Safety (Nov 2013) and Glaser, A .; Goldston, RJ (2012). "Proliferation Risks of Magnetic Fusion Energy: Clandestine Production, Cover Production and Breakout". Nuclear Fusion 52 (4): 043004. doi : 10.1088 / 0029-5515 / 52/4/043004
  25. TC Hender et al .: Fusion Technology , Section: Estimation of the investment costs for the essential elements of a fusion power plant . Vol. 30, December 1996.
  26. P. Lako et al .: Long Term Scenarios And The Role Of Fusion Power ( Memento of the original from September 23, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . February 1999 (PDF; 248 kB). @1@ 2Template: Webachiv / IABot / www.ecn.nl
  27. T. Hamacher, 2001: Fusion, Engineering and Design , pp. 55-57, 95-103.
  28. Delene, JG, J. Sheffield, KA Williams, RL Reid, S. Hadley, Vol. 39, no. 2, American Nuclear Society, March 2001: An Assessment of the Economics of Future Electric Power Generation Options and the Implications for Fusion ( Memento of the original dated November 11, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 329 kB). Retrieved July 22, 2013. @1@ 2Template: Webachiv / IABot / web.ornl.gov
  29. ^ Institute for Management (IIM), Max Planck Institute for Plasma Physics (IPP), Netherlands Energy Research Foundation (ECN): Longterm Energy Scenarios for India . 2002.
  30. Alexander M. Bradshaw (IPP), Reinhard Maschuw (FZK), Gerd Eisenbeiß (FJZ): Nuclear fusion (PDF; 15.1 MB). Brochure from Forschungszentrum Jülich (FZJ), Forschungszentrum Karlsruhe (FZK) and Max Planck Institute for Plasma Physics (IPP). 2006, pp. 45-49. Retrieved May 11, 2013.