Remanufacturing

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Remanufacturing in the nuclear industry

The reprocessing of nuclear fuels is part of the fuel cycle in nuclear technology . It serves to separate the substances contained in the used fuel elements of nuclear reactors and created during operation into recyclable parts (unused nuclear fuel and various radionuclides ) and high, medium and low level radioactive waste .

The chemical-physical processes used for this originally served military purposes. The aim was to obtain the bomb-proof plutonium , which does not occur naturally in usable quantities. In nuclear reactors, some of the non-fissile uranium- 238 is converted into plutonium-239 through neutron capture. This is cleavable, has a relatively low critical mass and can be separated chemically. Such a production of plutonium in the first nuclear reactors in the world operated with natural uranium and its separation from their fuel was therefore an inexpensive way of extracting bomb-proof material. In contrast, the sufficient enrichment of the isotope ²³⁵ U until it was bomb-proof according to the state of the art at the time (gas diffusion process) was extremely complex and lengthy, since the isotopes of an element cannot be distinguished chemically and can only be separated physically.

In the following, the reprocessing of spent fuel from light water reactors and fast breeders (breeding of plutonium-239 from uranium-238) with the PUREX process is treated. The THOREX process was developed for nuclear reactors that incubate uranium-233 from thorium-232 .

Remanufacturing details

When a fuel element burns down (left), the proportion of U ²³⁵ decreases , and new elements are created

The reprocessing allows fissile material to be separated from the other components of the spent fuel assembly and these also from one another. On the one hand, this enables new nuclear fuel to be obtained; on the other hand, the volume (but not the activity ) of the waste that has to be disposed of for long periods of time can be reduced to a small fraction. However, the reprocessing creates large volumes of secondary waste (e.g. contaminated water), the regulated disposal of which is very complex. Spent fuel elements from civil power reactors contain around 95% uranium and 1% plutonium . 10% of the uranium can be reused by re-enrichment. This enrichment process is usually not part of reprocessing. The spent nuclear fuel is currently usually stored temporarily without reprocessing. The Seversk camp in Russia is known here . Additional warehouses are located in Paducah, Kentucky and Portsmouth, Ohio .

The remaining 90% of the separated material is (in light water reactors) unusable uranium, fission products and the higher actinides, such as plutonium, formed by neutron capture . Further usable materials are obtained from this. Everything else is radioactive waste . Significantly smaller amounts of waste would result from the reprocessing of fuel for fast breeder reactors , as these can convert the U-238 into fissile plutonium.

In the context of the peaceful use of nuclear energy, the separated nuclear fuel, especially the plutonium, is processed into new fuel elements and returned to the reactor in the sense of recycling. In the military sector, the separation is used to preserve plutonium for nuclear weapons . Some higher actinides can also be selectively separated off in order to use them for special tasks.

An additional separation of the noble metals ruthenium , rhodium and palladium formed during nuclear fission is also conceivable during reprocessing. However, since the palladium obtained in this way contains not only 4 stable ones but also a radioactive, long-lived isotope ( ¹⁰⁷ Pd) with a half-life (HWZ) of 6.5 million years, this palladium should not be used outside of safety areas. In the case of rhodium and ruthenium, the facts are more favorable, since of these precious metals only radioactive isotopes with half-lives of a maximum of one year are present in the fission products, so that use outside the safety range would be possible after one to two decades (radioactivity drop to one millionth). To date, the separation of ruthenium, rhodium and palladium from the cleavage products is not practiced.

This means that a total of 1% to 10% of the material has to be reused through reprocessing, 90% to 99% are radioactive waste. Its main amount consists of the fission products of nuclear fission and their decay products, that is, radioactive isotopes of all elements with mass numbers between 77 and 158 (in the PSE the elements from arsenic to terbium ). From these artificial radioisotopes , those that can be used in science, technology or medicine as a radiation source or to track material flows are separated during reprocessing. The remaining fission products are separated into those with high, medium and low radioactivity because their storage is handled differently. Of the total volume of this waste, 7.3% are high-level waste, which, however, contains 98.3% of the total radioactivity. This leaves 1.7% of the radioactivity and almost 92.7% of the total volume for medium and low level radioactive waste.

The reprocessing also produces radioactively contaminated wastewater, which is usually discharged into the environment. For example, around 0.5 billion liters of radioactively contaminated wastewater is discharged into the English Channel every year at the La Hague reprocessing plant . Radioactively contaminated exhaust air is also released. The proportion of radioactive krypton ( ⁸⁵ Kr; beta emitters with a half-life of around 10 years) in this exhaust air is particularly significant at around 90,000 Bq per cubic meter of air.

Procedure

In a reprocessing plant, the fuel elements are first mechanically cut and dissolved in hot nitric acid. To separate the components of uranium, plutonium, the higher actinides and fission products from each other are employed to extraction with the PUREX process a (PUREX = English plutonium-uranium recovery by extraction ). As the extraction agent is tributyl phosphate (C ₄ H ₉ O) ₃ , PO, the 70 percent C _12-14 - alkanes (for example, kerosene is diluted). An almost complete separation of the components can be achieved by performing the extraction cycles several times.

Alternative procedures

In addition to the method described above, newer methods of pyrometallurgy have been developed in the United States and Russia. In principle, electrolysis is used to separate the metals. The main advantage compared to the PUREX process is that the uranium is separated as a mixture together with plutonium and higher actinides, making it more difficult to isolate weapons-grade plutonium. Another advantage is that the remaining radioactive waste only needs to be stored for around 500 years.

A process that is in the conceptual stage is the rotating shaft reactor . This type of nuclear reactor is intended to "process" a large part of its own fuel that has been consumed during operation, thereby leaving far less material to be disposed of per unit of energy generated. So far, no rotor shaft reactor has been built.

The dual-fluid reactor is also at the concept stage , in which the fissile materials would be continuously removed during operation and which uses fractional distillation / rectification for this purpose. In theory, one could also process and use spent fuel elements in a DFR.

At the beginning of January 2011, reports from Chinese scientists emerged about the alleged development of a new reprocessing method that would make uranium use 60 times more efficient.

Further processing of the products

During civil reprocessing, the separated plutonium is mostly processed into new uranium / plutonium fuel elements ( MOX fuel elements ), which are reused in light water reactors . This is the case in France, Germany and Japan, for example. In Great Britain the plutonium is only stored due to the lack of recycling possibilities. A much more efficient use in comparison to light water reactors would be possible in breeder reactors , but this has not caught on worldwide.

So far, the separated uranium has only been recycled to a relatively small extent. Since, in contrast to natural uranium, it still contains small traces of undesired isotopes, further processing is more complex and therefore currently uneconomical.

After so-called partitioning , the radioactive fission products and the higher actinides are initially available as a highly radioactive solution that is stored in cooled stainless steel tanks. With a view to long-term interim storage and subsequent disposal , this waste must be brought into a solid and leak-resistant form. Glazing has proven to be a suitable method for this. Vitrification systems are therefore also installed in all existing reprocessing plants . During the vitrification, the solution is first dried and the solids which have precipitated out of the solution are mixed with glass-forming substances and glass blocks are melted from them. The non-radioactive solvent is released and can be used again.

Environmental impact

During reprocessing, waste gases and waste water are produced, which are cleaned and then discharged into the environment. Despite the cleaning measures, these discharges still contain radioactive components. The maximum amount of activity that may be released into the environment with the exhaust air and wastewater is specified by the responsible authorities in the operating license. These limit values ​​are based on the calculation of the radiological effects on the people in the vicinity of the plant. Therefore, the permissible derivation values ​​are heavily dependent on the geographical conditions of the location. Environmental protection associations such as Greenpeace , citing their own measurements, have repeatedly accused the operators of the reprocessing plants of polluting the environment in an inadmissible manner.

Reprocessing plants

A reprocessing plant (WAA) is a large-scale plant in which spent fuel elements from nuclear power plants are chemically reprocessed, ie separated into radioactive waste (nuclear waste) and reusable fissile material (especially uranium , plutonium ). The PUREX process has established itself as a process. The reprocessing plants thus represent an attempt to build an atomic recycling cycle. The radioactive waste that arises during reprocessing is processed (conditioned) on site and later returned to the respective customer.

A total reprocessing capacity of around 5000 tSM / a (tons of heavy metal per year) is available in the civil sector (2900 tSM / a for fuel from light water reactors, 2100 tSM / a for other fuels).

fuel	investment	Capacity in tonnes per year
LWR fuel	La Hague, France	1700
	Sellafield, UK	600
	Mayak, Russia	400
	Rokkasho, Japan	700 (not yet completed)
Other fuels	Sellafield, United Kingdom (Magnox)	1500
	India (PHWR)	330
	Tōkai, Japan (MOX)	40

Systems in operation

• Great Britain : In Sellafield , formerly called Windscale , two plants are in operation. The older B205 facility is used to process spent metallic fuel elements from the British Magnox reactors . The newer THORP Plant (Thermal Oxide Reprocessing Plant) is designed for the reprocessing of oxide fuels, both from the British Advanced Gas-cooled Reactors and from light water reactors originate abroad.
• France :There are also two reprocessing plantsin La Hague . The UP2-800 / La Hague facility is intended for French fuel elements. The relatively similar facility UP3 / La Hague is used for the reprocessing of spent LWR fuel elements from foreign customers.
• India : In India, the first small plant for the reprocessing of research reactor fuel was put into operation in 1964 ( Trombay ). A larger facility for fuel assemblies from power reactors is located in Tarapur . The commissioning of another plant at Kalpakkam began in early 1997.
• Japan : A plant has beenin operationin the village of Tōkai since 1977. After a fire and subsequent explosion in the waste bitumen plant in March 1997, operations were stopped and resumed in November 2000.
• Russia : Two reprocessing plants are in operation (RT-1 / Mayak , Tomsk ). Littleinformation is availableabout other systems in Tomsk or in Zheleznogorsk (RT-2).
• USA : The Savannah River Site ( South Carolina ),originally built primarily for military purposes,is still used today for the reprocessing of fuel elements from research reactors, including those from abroad.
• North Korea : In Nyŏngbyŏn , North Korea operates a reprocessing plant in addition to a research reactor. Like the reactor, it should currently be unsealed and in operation to extract the plutonium from the reactor.

Planned or under construction facilities

The following parts of this section seem since 2016 is out of date to be : The year 2016 is over. Has it gone into commercial operation?
Please help to research and insert the missing information .

• Japan : Rokkasho reprocessing plant : A larger plant in Rokkasho is under construction. The construction work was delayed several years behind the original schedule. Commissioning tests began at the end of 2004. Commercial commissioning is planned for 2016.

Decommissioned plants

• France : The UP1 facility in Marcoule , which originally served military purposes and in which Magnox fuel elements were later reprocessed, was finally shut down in 1997 after there are no longer any Magnox reactors in operation in France .
• Belgium : From 1967 to 1974the reprocessing plant Eurochemic , a joint project of 13 member states of the OECD , was operatedin Mol . A total of around 210 t of fuel were processed in this plant. The dismantling of the facilities began in 1991.
• USA : In the post-war years several reprocessing plants were built for military use ( Hanford , Savannah River Site , Idaho ). Idaho (1992) and Hanford (1990) were shut down a few years ago. A commercial facility in West Valley operated from 1966 to 1971. Two more plants ( Barnwell , Morris ) were completed, but not put into operation for different reasons.
• Germany :
  • Karlsruhe reprocessing plant (WAK) - From 1971 to 1990 the WAK was in operation on the premises of the Karlsruhe Research Center. As a pilot plant, it had the purpose of gaining operational experience for the operation of a large plant (for example the planned Wackersdorf reprocessing plant ). During its operating time, a little more than 200 t of nuclear fuel was reprocessed in the WAK.
  • Jülich reprocessing plant - For spherical fuel elements from the THTR-300 , a thorium high-temperature reactor in Hamm-Uentrop (construction period 1970–1983) and the smaller AVR , a " reprocessing plant " called 'JUPITER' was built in Jülich . It should enable a thorium cycle. However, the fuel elements had a design error; therefore JUPITER never went into operation .

Dropped projects

• Germany : Wackersdorf reprocessing plant - The reprocessing plant planned in the 1980s in Wackersdorf , Bavaria , was never completed. At that time there were major protests by opponents of nuclear power against this WAA (for example the Anti-WAAhnsinns Festival of 1986 in Burglengenfeld ). Plans by the Hessian state government from June 1980 to implement a plant in Volkmarsen were also abandoned after severe criticism.

Arguments for Remanufacturing

The reprocessing reduces the space required for final disposal because the highly radioactive material that belongs there is separated off. Its volume is only around 2 to 3% of the original volume: only uranium-235 is used as fuel in the fuel elements, of which enriched uranium contains 3 to 4% and non-enriched uranium only 0.72%. Over the life of a fuel element, around 0.9% of this isotope is converted into plutonium and around 60 to 70% is split. Only some of the fission products are high-level radioactive waste intended for final disposal.

It is difficult to predict how long the natural uranium deposits will last for the world's electricity supply. Estimates range from 25 years to well over 100 years, each of which could be increased by a factor of around 50 with the more efficient use of uranium in breeder reactors . The estimate depends, among many other factors, on the uranium price (nuclear fuel only accounts for around 20% of the electricity costs in light water reactors) and on how much nuclear energy will be used in the future. While Germany is planning to phase out the use of nuclear power, new nuclear power plants are being built in other countries such as Finland, France, Canada, Russia, India and, above all, China. In this way, China will ensure a net increase in uranium consumption worldwide, despite the decline in demand in some other countries. Worldwide, 63 power plant blocks are under construction in mid-2012, 160 are in the planning and another 329 are planned for the long term. Against this background, the reprocessing of used fuel elements could one day be necessary in order to be able to extract the remaining uranium-235 and Pu-239 from the remaining uranium.

Arguments against remanufacturing

The argument that the recovered fissile material can be reused is currently not economically viable, since at today's uranium prices, fuel elements made from reprocessed material are significantly more expensive than fuel elements made from “fresh” uranium. Compared to direct disposal, reprocessing causes 10 to 18 percent higher fuel cycle costs. With increasing demand for uranium, for example due to new Chinese nuclear power plants and a decrease in natural deposits, reprocessing can become more and more economically interesting in the future. In order to be able to reprocess uranium at a later time, however, fuel rods must not be disposed of or must be retrievable.

See also : breeder reactor

Reprocessing plants can be used to extract weapons-grade plutonium and for this reason are operated by all nations with their own nuclear weapons program. Purely military plants usually differ technically from civil reprocessing plants, since military and civil use pursue different goals: For military use, fuel elements with very little burnup are required, i.e. H. with a short residence time in the reactor and thus low contamination with fission products. Commercial electricity suppliers, on the other hand, want to leave the fuel elements in the reactor for as long as possible in order to get the most out of the material. These higher spent fuel assemblies require more effort in reprocessing because of the considerably larger proportion of fission products. Plutonium from the relatively highly spent fuel elements of conventional power reactors is not suitable for the production of military- grade nuclear weapons . Nevertheless, it cannot be denied that even in civilian reprocessing, plutonium is separated and thus the technology for military processing is made more accessible. Preventing abuse through controls is one of the tasks of the international safeguards system and the subject of international agreements, in particular the Nuclear Non-Proliferation Treaty , the Safeguards Agreement and the Additional Protocol .

The radioactive discharges into the sea , especially from the European plants in Sellafield and La Hague, are also controversial . While on the authority of environmentalists such as Greenpeace , the derivatives to an unacceptable pollution of the seas and on the food chain to a radiation exposure cause the population, operators refer to comply with the limits and the low radiological consequences for the people .

While the volume of high-level radioactive waste decreases by 80% through a single reprocessing, the volume of low- and medium-level waste increases five-fold.

Numerous transports to and from the reprocessing plants are necessary for the delivery of the fuel elements and the return transport of the residues and waste. The Castor transports between the reprocessing plants and Germany have been hindered time and again in the past. Since 2005 no more spent fuel elements have been delivered to reprocessing from Germany. In fact, Switzerland has not delivered any fuel elements to the WA since 2006; In 2017, the ban on the reprocessing of fuel elements was enshrined in the Swiss Nuclear Energy Act (KEG).

The historian Joachim Radkau summed up in 2011:

“At first, reprocessing also had a good sound in circles close to the eco-scene, it was seen as an ecologically exemplary way of recycling leftovers. From a distance, it seemed quite sensible to remove the highly radiating plutonium from the nuclear waste and use it again in nuclear power plants - I thought the same way - it was only gradually that you realized that reprocessing is associated with its own insidious risks The saying about the devil in detail applies to many areas of nuclear power - reprocessing is the best example of this. "

Some countries, such as Germany and the USA, have decided against carrying out reprocessing in their own country for economic and political reasons.

See also

• Nuclear Power Plant Safety
• Karlsruhe reprocessing plant
• Contaminated sites in the seas # Radioactive substances
• THORP # story
• Head-end

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1. ^ RH Rainey, JG Moore: Laboratory development of the acid THOREX PROCESS for recovery of consolidated Edison Thorium rector fuel. OAK RIDGE NATIONAL LABORATORY, ORNL-3155, 1962, Archived copy ( Memento of January 14, 2010 in the Internet Archive )
2. ↑ arte TV: " Nightmare nuclear waste ". Documentary by Eric Guéret & Laure Noualhat (German broadcast October 15, 2009)
3. ↑ kernenergie.ch
4. ^ Reprocessing in La Hague Greenpeace ( Memento from November 5, 2010 in the Internet Archive )
5. ↑ arte TV: " Nightmare nuclear waste ". Documentary by Eric Guéret & Laure Noualhat (German broadcast October 15, 2009)
6. ^ William H. Hannum, Gerald E. Marsh, George S. Stanford: Smarter Use of Nuclear Waste. In: Scientific American. December 2005, p. 64 ff.
7. ↑ IFK: As with schnapps distilling - the PPU. Retrieved August 18, 2018 . 
8. ↑ Recycling of uranium: China reports breakthrough in nuclear technology. Spiegel Online , January 3, 2011, accessed January 4, 2011 . 
9. ^ PK Dey, NK Bansal: Spent fuel reprocessing: A vital link in Indian nuclear power program . In: Nuclear Engineering and Design . tape 236 , no. 7-8 , April 2006, pp. 723 , doi : 10.1016 / j.nucengdes.2005.09.029 (English).
10. ^ World Nuclear Association: Processing of Used Nuclear Fuel
11. ↑ HTR fuel cycle - technology and strategy . U. Tillessen, E. Merz, 9 pages. Undated, according to footnote 52 November 1974.
12. ↑ Peter Diehl: Greenpeace Uranium 2006 report . 01, 2006, p. 58.
13. ↑ Uranium as a nuclear fuel: occurrence and range . 03, 2006, p. 5.
14. ^ World Nuclear Association: World Nuclear Power Reactors & Uranium Requirements.Retrieved May 2012.
15. ↑ ILK statement on the reprocessing of spent fuel assemblies ( Memento of December 12, 2011 in the Internet Archive ) (PDF; 112 kB) International Joint Commission on Nuclear Technology, November 2001, p. 6. Accessed on October 9, 2012.
16. ↑ Energiespiegel Nr. 7 ( Memento of January 18, 2012 in the Internet Archive ), Paul Scherrer Institute, 2002, p. 1.
17. ↑ Greenpeace on reprocessing ( Memento from October 12, 2007 in the Internet Archive )
18. ↑ SR 732.1 Nuclear Energy Act (KEG) of March 21, 2003, status 2006 and May 22, 2017, Article 9 "Reprocessing", in the portal of the Swiss government
19. ↑ Joachim Radkau: The era of ecology. Beck Verlag, 2011, ISBN 978-3-406-61372-2 . Quoted from Peter Leusch: History of the anti-nuclear movement

Web links

• LWR Recycle: Necessity of Impediment? GS Stanford in Proceedings of Global 2003, ANS Winter Meeting, New Orleans, November 16-20, 2003. PDF (65 kB)