How can I convert mercury into gold

Transmutation

Under Transmutation one understands the conversion of atomic nuclei into other nuclides, for example through nuclear reactions. Possible applications are:

Originally the term was used by alchemists, among whom the belief held for centuries chemical Means of being able to turn other elements into gold.

Nuclear technology / nuclear transmutation

The term is used in nuclear technology Transmutation for the externally induced conversion of atomic nuclei into other elements. Usually this means a special procedure. In the future, it will be used to convert long-lived, highly toxic radionuclides, such as those produced during the operation of nuclear power plants, into more short-lived or less toxic substances.

preparation

For all conceivable methods, it must be taken into account that the transmutation takes place specifically for each nuclide. Therefore, the first step of all processes is the separation (partitioning) of the individual nuclides, at least with the secondary goal of keeping the overall increase in volume small. In this process step and in further process steps, however, the total amount of waste to be treated is generally and inevitably initially increased.

A transmutation is completely unsuitable for the comparably large and predominant amount of low-level radioactive mixed waste. The landfilling of mixed radioactive waste is never replaced by transmutation, with or without volume reduction.

Transmutation by neutrons

Plutonium-239 and uranium-233 have been extracted from uranium-238 and thorium-232 on an industrial scale since the 1940s. This was one of the key techniques in building the great arsenals of nuclear weapons during the Cold War.

The term activation is common for the general conversion of non-radiating material into radioactive material. It can never be completely avoided in nuclear reactors and is a reason for the generation of radioactive waste in the operation of nuclear power plants. When transmutation with neutrons leads to nuclides that can again serve as nuclear fuel, it is also referred to as breeding. Reactors that are designed for this process to take place particularly efficiently are therefore called breeder reactors.

In concepts of the 1970s for the extensive replacement of coal and crude oil as energy sources with nuclear energy, transmutation in breeder reactors was envisaged as part of a nuclear fuel cycle. Not only is the comparatively rare uranium isotope235U used it but it's also the much more common one 238U can be used, which is then converted into fissile plutonium. In this process, more plutonium is hatched than 235U is consumed. In this way, the uranium deposits should be used as efficiently as possible. The breeder reactor at Kalkar planned in Germany next to the KNK-II in Karlsruhe for the realization of the concept was built, but mainly because of technical reasons[1], but also because of political concerns, it was never put into operation. It has not been possible anywhere in the world to implement such a reactor beyond the experimental stage. The "Superphénix" breeder reactor, which was built in France from 1974 to 1981 but only commissioned in 1985, was only in operation for 180 days until it was closed in 1990.[1] From 1992 until the final shutdown in 1998, the reactor was used to generate electricity again. However, the reactor concept consumes considerable amounts of electricity to keep the sodium in the cooling system liquid.[2], which among other things contributes to inefficiency.

Transmutation with neutrons generated by spallation

At the end of the 1980s, Nobel Prize winner Carlo Rubbia presented an alternative reactor concept, called Rubbiatron, to transmutation. This provides a lead-bismuth alloy as a coolant, which, due to the high atomic weights of lead and bismuth, practically no longer brakes the neutrons, so that the reactor has a very high proportion of high-energy neutrons during operation. Furthermore, the Rubbiatron contains an external neutron source, a so-called spallation source, which enables the reactor to be operated subcritically (see also subcritical reactors). This is necessary because, given the high neutron energies and fuels provided (in particular the transuranic elements americium and curium, which are produced in small quantities in normal nuclear reactors), stable, critical operation is impossible or only possible with great difficulty; there are also safety advantages compared to a critical working reactor. However, the operation takes place so close to the criticality point that each neutron from the spallation source in the reactor generates dozens of secondary neutrons on average.[3]

The spallation source consists of a strong particle accelerator, which shoots a large number of high-energy protons (typical energy up to 1 GeV) onto the liquid lead-bismuth alloy, which is also used as a coolant. Each proton releases up to 20 or more neutrons which, due to the high energy of the lead nucleus, literally evaporate.[3] Secondary protons are also released, which, due to their significantly lower energy, usually do not trigger any further nuclear reactions[4]

One of the advantages of the Rubbiatron compared to conventional reactors is that it can be regulated quickly and reliably: If the spallation source is switched off, the nuclear reaction dries up on time scales that correspond to the lifetime of the neutrons in the reactor.[5] So you do not have to rely on the retraction of control rods to interrupt the chain reaction. Of course, a form of control is also required in the Rubbiatron in order to keep the distance to the criticality point constant even if the original inventory is increasingly consumed. Depending on the composition of the core, the reactivity increases or decreases during operation.[3]

However, other problems of conventional reactors, in particular the decay heat, also exist in transmutation systems. Like other nuclear reactors, they too would therefore need emergency cooling systems. In addition, when large amounts of americium and curium are loaded, a considerable amount of heat is generated due to their comparatively short half-lives and high decay energy. If uranium, thorium and / or plutonium are also used as fuel, the amount of fission products produced and possibly even the amount of short-lived actinides produced exceeds the amount of actinids consumed (ie “transmuted”).

A test facility for transmutation called XT-ADS is currently being planned at the Belgian nuclear research center SCK-CEN. The reactor is to be operated with 50 to 100 megawatts of thermal output (corresponding to approx. One eightieth to one thirtieth of the output of typical commercial reactors for electricity generation) and a criticality value of 0.95 (corresponding to 20 times the neutron multiplication) with conventional MOX fuel elements.[3] The follow-up project EFIT could work with 400 megawatts of thermal energy, a criticality of 0.97 (corresponding to 33 times the neutron multiplication) and an increased proportion of minor actinides in the fuel. Here, too, uranium and plutonium will make up the bulk of the fuel.[3]

Nuclear Waste Disposal

To date, no transmutation facility for the disposal of nuclear waste has been implemented anywhere in the world. Smaller laboratory-scale systems for transmutation have only been implemented in the context of research projects. The few existing breeder reactors are used without exception for plutonium production.

A European research facility is currently planned in Mol, Belgium, which could be ready in 2023[6]. The experimental reactor there Myrrha (Multi-purpose Hybrid Research Reactor for Hightech Applications)[7] According to the current state of knowledge, it should not only remove nuclear waste, but also produce electricity. Around 15 percent of the energy generated would be used for the particle accelerator and another part for the system itself, the rest could be fed into the grid. The biggest problem is filtering out the minor actinides, such as neptunium, americium and curium, with which the system has to be specifically charged.[8] The time required for the final disposal of the residual waste is to be drastically reduced from 500,000 years to a theoretical value for the remaining final disposal time of around 500 years; 1,500 years are realistic.[9] At the end of 2010, the secured total budget was € 1 billion. Experimentation is to begin in 2024.[10] It is hoped to be "ready for industry" in about 30 years[11]without, however, having previously provided evidence of technical feasibility or economic viability as a basis. In the US project Accelerator-Driven Transmutation (ATW), which compared to the European "Rubbia Project"[12] is considered to be the more realistic project at the moment[13][14]In 1999, the time horizon for the process demonstration was assumed to be 2027, the implementation time to 90 years, the investment costs to the prototype at US $ 9 billion and the operating costs at US $ 280 billion.[14] In more recent considerations, an investment volume of € 383 million and operating costs of € 20 million / year are assumed for a first plant for transmutation[12](P.18) or several hundred million euros until the realization[15]. The actual reduction in radioactive waste by a plant was put at 227 kg per year, since the process itself also creates new uranium-233[12](P.19).

Manufacture of gold and other precious metals

Gold can be produced in a nuclear reactor by irradiating platinum or mercury. Since platinum is almost as expensive as gold, it is uneconomical as a starting material. Of the mercury, only the isotope can196Hg, which is contained in natural mercury with a content of 0.15%, increases when irradiated with slow neutrons through neutron capture 197Hg, which is then converted into the only stable gold isotope by electron capture with a half-life of 64.14 hours 197Au is falling apart. The other mercury isotopes transform into one another when irradiated with slow neutrons or form mercury isotopes that transform into thallium through beta decay. With fast neutrons the isotope of mercury 198Hg, which is 9.97% in natural mercury, by splitting off a neutron into the mercury isotope 197Hg, which then (as described above) disintegrates into gold. However, this reaction has a smaller cross-section and could only be carried out in fast breeders or with spallation neutron sources. It is also conceivable to knock several neutrons out of the other isotopes of mercury with very high-energy neutrons to produce mercury 197Hg. However, such high-energy neutrons can only be generated with the help of particle accelerators.

Because of its low efficiency, gold synthesis is of no economic importance.

Spent fuel elements from nuclear power plants contain a few percent fission products, of which a few percent are stable rhodium and ruthenium. The radioactive isotopes of the same elements formed in parallel, with half-lives of 45 days and 373 days, respectively, make separation and use more difficult. Stable palladium is also formed during nuclear fission in proportions of a few percent. However, the radioactive isotope of palladium is also produced in a comparable amount 107Pd with a half-life of 6.5 million years. Therefore, in addition to chemical separation, complex isotope separation would be necessary for use.

literature

  • Mikhail Kh. Khankhasayev: Nuclear methods for transmutation of nuclear waste - problems, perspectives, cooperative research. In: World Scientific Publ. 1997, ISBN 981-02-3011-7.

Web links

Individual evidence

  1. 1,01,1Eric Tschöp: Uranium mining and uranium export - a "cycle" with side effects, inserted March 16, 2012
  2. ↑ Cour des comptes: Public report 1996 (archived version of the Internet Archive dated November 26, 2006)
  3. 3,03,13,23,33,4Alex C. Mueller: Transmutation of radioactive waste. In: Physics Journal 11 (2010). Pp. 33-38.
  4. Spallation - third generation neutron source. World of physics. Retrieved January 22, 2011.
  5. ↑ Uta Defke: Nuclear waste under attack. In: Frankfurter Allgemeine Sonntagszeitung of April 23, 2006, p. 69.
  6. ↑ RW TH Aachen: Kettler_AGATE_2011 concept, inserted March 22, 2012
  7. ↑ Paul Schuurmans, January 23, 2007: The Myrrha / XT-ADS project, inserted March 16, 2012
  8. ↑ Ulli Kulke: Broadcast. In: The world. September 15, 2010, archived from the original on September 24, 2010, accessed on September 24, 2010 (German).
  9. Nuclear waste under fire - In Belgium, researchers are planning a facility that will defuse highly radioactive waste. In: Sunday newspaper. Zurich, November 20, 2010
  10. ↑ EIKE November 2010: Partitioning and Transmutation], inserted March 16, 2012
  11. ↑ Physik-Journal 9 (2010) No. 11: Transmutation of radioactive waste, inserted March 16, 2012
  12. 12,012,112,2Michael Czopnik, Bachelor thesis September 2010: Accelerator-driven systems for the transmutation of radioactive waste, added March 22, 2012
  13. ↑ Eckhard Rebhahn: Energy manual - Table of contents, ISBN 3-540-41259-X.
  14. 14,014,1Eckhard Rebhahn: Energy manual, Google Book Preview on Transmutation, added March 22, 2012
  15. ↑ R. Brandt, W. Westmeier, University of Marburg, January 2007: Applied research on transmutation, inserted March 22, 2012