# Breeder

A breeder reactor is a nuclear reactor that is used to generate energy with the simultaneous generation of further fissile material. A non-fissile nuclide is converted into a fissile one, which can then be used as a nuclear fuel (after processing and incorporation into new fuel assemblies) . This conversion (as conversion , sometimes also referred to as breeding , see conversion rate ) takes place in every nuclear reactor, but one speaks of a "breeder reactor" or "breeder" only when it produces more fuel than it does itself in the same time consumed.

Fast breeder reactor in basin design (left) and in loop design (right)

The first breeder reactor was the Experimental Breeder Reactor I . In 1951, it was the first nuclear reactor in the world to generate electricity with its thermal output. Today the only breeder reactors in commercial operation are the BN-600 and the BN-800 in Russia (as of 2015). Some experimental breeder reactors are in operation, construction or planning, especially within the Generation IV International Forum research network .

The purpose of the breeder reactor development is the far better utilization of the nuclear fuel. With breeder reactors around 60 times more energy could be obtained from natural uranium than with light water reactors . The development of breeder reactors received state funding in many industrialized countries from the 1960s to 1980s, for example in the German project Fast Breeder from 1962 to 1989.

When the US and Russia developed their nuclear weapons, special reactors (e.g. the ADE reactor ) were built for this purpose , which had the sole purpose of producing plutonium. These use moderated, i.e. thermal neutrons and are not considered to be breeder reactors.

## Types of breeder reactors

There are two types of breeder reactors and they are named after the energy spectrum of the neutrons used :

Fast breeders
Fast breeders work with uranium- 238 (or more rarely thorium- 232) as a breeding material and with fast neutrons, as they are released in nuclear fission, i.e. without a moderator . Uranium-plutonium mixed oxide ( MOX ) is used as the nuclear fuel . The breeding zone ( see below ) contains natural or depleted uranium oxide, which mainly consists of 238 U. The fast breeder makes it possible to use the natural uranium deposits more than 50 times more efficiently, but this requires the development of a plutonium economy for many types of reactors. Its name does not mean that it “breeds quickly”, it only refers to the fast neutrons.
Thermal breeders
Thermal breeders work with thorium as the breeding material and with predominantly thermal neutrons . After an initial filling with enriched uranium oxide, plutonium oxide or MOX, 232 Th becomes fissile 233 U through neutron deposition and beta decay . This technology is interesting because of the large thorium deposits, which are about three times larger than the uranium deposits.

Noteworthy are concepts for so-called. "Advanced Pressurized Water Reactors " (Advanced Pressurized Water Reactors) or boiling water reactors "with reduced Moderation". They would work with conventional fuels and coolants, but thanks to their design they would achieve high conversion rates of 0.7 to 1.0 (hence sometimes also referred to as upconverters ), so they would be “almost” breeder reactors.

## Fast breeder

### Construction of the reactor

The reactor core consists of many vertical, with z. B. uranium - plutonium - mixed oxide filled stainless steel tubes ( fuel rods ). The rods are bundled to form fuel assemblies and fill an approximately cylindrical area of ​​z. B. 3 m high and 5 m in diameter. The chain reaction (see also criticality ) is controlled by control rods made of boron steel or another neutron absorbing material.

The reactor core is divided into an inner gap and an outer breeding zone. The coolant - which in these reactors must not act as a moderator as in the light water reactor - is a liquid metal such as sodium or potassium . Concepts for gas-cooled breeder reactors were also investigated until around 1970, but were not used.

### Fuel breeding process

The natural uranium consists of 99.3% of the non-fissile isotope 238 U and only 0.7% of the fissile isotope 235 U. For the operation of most nuclear fission reactors (e.g. light water reactor ) it has to be technically necessary before the fuel elements are manufactured consuming% to approximately 3 to 4 235 U enriched be.

In the operation of every uranium reactor, part of the existing 238 U is converted into 239 U by neutron capture . This passes over by itself through two successive β - decays into the fissile 239 Pu, which is partly split again in the reactor parallel to the 235 U, but partly can also be processed into new mixed oxide fuel elements later after reprocessing the used fuel .

${\ displaystyle \ mathrm {^ {238} _ {\ 92} U \ + \ _ {0} ^ {1} n \ \ longrightarrow \ _ {\ 92} ^ {239} U \ {\ xrightarrow {\ beta ^ {-}}} \ _ {\ 93} ^ {239} Np \ {\ xrightarrow {\ beta ^ {-}}} \ _ {\ 94} ^ {239} Pu}}$

The “breeding” in the true sense, i.e. an excess of the fuel produced in this way over the fuel consumed at the same time, is only possible in a reactor that works without a moderator , a fast breeder , because the average number is only new when it is split by a fast neutron released neutrons per fission high enough for this (see nuclear fission process in the breeder reactor ). The excess is expressed in the fact that the breeding ratio (sometimes also called breeding rate or conversion rate ), the number of newly generated fuel atoms per fuel atom used, is above 1.0.

The fast breeder is not so named because it “breeds quickly”, but because it uses fast instead of thermal (decelerated) neutrons to split the nucleus .

### Better utilization of nuclear fuel stocks

The 238 U has only a few other uses besides its use in the breeder reactor (including uranium ammunition ). With a network of breeder reactors, reprocessing and light water reactors, the earth's uranium reserves could provide around 60 times as much energy as if only the 235 U were split. In theory, the complete utilization of the 238 U would even result in a usage factor that is over 100 times higher, but this is currently not technically feasible.

The use of the metal thorium 232 Th, which was already used as a breeding material in the THTR-300 reactor from 1983 to 1989 and which produces fuel 233 U, would again significantly improve the resource situation of nuclear power, since the natural thorium deposits that of uranium exceed many times.

### Cleavage zone

Fast neutrons trigger new nuclear fission with a much lower probability (see cross section ) than thermal neutrons. Therefore, compared to moderated reactor types, the fissile material concentration in the fission zone must be increased. The fissile material is a mixed oxide of 15 to 20% plutonia and 80 to 85% uranium oxide ; the concentration of the fissile isotopes is about ten times higher than that of the light water reactors. As a coolant - which must not have a moderating effect in the fast reactor, i.e. must have a sufficiently high mass number - the previous breeder reactors use liquid sodium ; Concepts with gas cooling were also examined. The first experimental breeder reactors in the USA and in the former Soviet Union still used mercury as a coolant, which u. a. however, caused problems due to corrosion.

### Brood mantle

The breeding blanket is arranged around the fissure zone and completely surrounds it. The upper and lower parts of a fuel rod in the fission zone are not filled with mixed fuel oxide like the middle part, but with depleted uranium oxide as a breeding material; the rods located radially further out contain this over their entire length. Depleted uranium is the residue that inevitably occurs in the uranium enrichment process.

### Nuclear fission process in the breeder reactor

"Brooding" requires that the fission of an atomic nucleus releases more than two neutrons on average, because one neutron is required to trigger the next fission ( criticality of the chain reaction) and another neutron must generate a new fissile nucleus to replace the fissured nucleus , i.e. to achieve a breeding ratio of 1.0. In addition, there are inevitable neutron losses through leakage to the outside and through absorption processes that neither lead to fission nor to Pu production, namely absorption in the structural material, in fission products , in the coolant and in the control rods .

With a few simplifications, the relationships can be well described by the generation factor (eta), the number of newly released neutrons per neutron absorbed in the fission material . This number is slightly smaller than that of the neutrons released per fission , because not every absorption in the fission material leads to fission. In the case of fission by thermal neutrons, the easily fissionable nuclides 233 U, 235 U and 239 Pu are only slightly above 2.0. When cleaved by fast neutrons with an energy of 1 MeV, on the other hand, 239 Pu releases about 2.8 neutrons. This means that even with losses of around 0.5 neutrons per neutron absorbed in the fuel, significantly more than 1 new fissile core can be generated per fissioned core. ${\ displaystyle \ eta}$${\ displaystyle \ eta}$

### Energy generation

The mostly two fragments (“fission fragments”) that arise when a nucleus is split carry the energy gain of the reaction, a total of around 200 MeV , as kinetic energy . They are slowed down in the surrounding fuel material and heat it up. The primary sodium cooling circuit absorbs the heat and passes it on to a secondary sodium cooling circuit via a heat exchanger. This secondary circuit produced in a steam generator steam , which - as in a conventional coal- or oil-fired power plant - the turbine drives. The turbine converts the flow energy of the steam into rotational energy, which a generator converts into electrical energy. The exhaust steam leaving the turbine is liquefied again in a condenser and fed into the steam circuit. The condenser is cooled by an external cooling circuit, which, for example, transfers the heat to running water.

### Cooling circuits

The breeder reactor technology is based in some areas on the fundamentals of light water reactor technology , but has some essential differences. The heat transfer medium sodium is characterized by high thermal conductivity and a large usable temperature range. It melts at 98 ° C and boils at 883 ° C. Because of this high boiling point, a pressure of only about 10 bar is required in the sodium circuit, which is a certain safety advantage.

In contrast to the light water reactor, a second sodium circuit ( secondary circuit ) is switched on between the sodium circuit , which cools the fuel elements ( primary circuit ), and the water-steam circuit . Although this reduces the efficiency , it is necessary for safety reasons so that only non-radioactive sodium reacts with water even in the event of a steam generator leak. One or more intermediate heat exchangers transfer the heat from the primary to the secondary coolant. In the German breeder reactor constructions the so-called loop system was used, in which all pumps and heat exchangers are spatially separated from the reactor and the reactor tank is filled with nitrogen above the sodium . In the pool system , which is used more frequently in other countries, the primary circuit including primary pumps and intermediate heat exchangers is located in the reactor tank itself, with argon being used as a protective gas in the tank. In any case, when the reactor is switched off, the sodium in the cooling circuits must be kept liquid by external heating.

### Security - pros and cons

Compared to light water reactors , for example , the operation of a breeder reactor requires different safety equipment. Physical reasons for this are primarily the not “automatically” negative vapor bubble coefficient , as well as the lower proportion of delayed neutrons from the fission compared to uranium .

Sodium vapor formation or loss does not automatically make the reactor subcritical . Instead, in such a case, the subcriticality must be established quickly and reliably using technical means. For this purpose, in addition to the normal control rods, breeder reactors have additional, independent sets of safety or shutdown rods which, if necessary, can fall into the reactor core or be “shot” into it ( scram ). Such a shutdown is triggered by sensitive systems to detect excess temperatures and boiling processes.

The smaller delayed neutron component in uranium-plutonium mixed oxide fuel means a smaller distance between the operating points “Delayed critical” and “Prompt critical” (see criticality ). This is taken into account by means of correspondingly sensitive, precise measurement of the neutron flux and the rapid response of the control rod system.

The large amount of plutonium , which is much more hazardous to health compared to uranium , is another safety challenge.

A risk of breeding technology with sodium cooling lies in the large-scale handling of the coolant, which can cause fires in contact with air or water.

Sodium cooling can in principle be operated at normal pressure due to the boiling temperature of sodium of 890 ° C. In comparison, light water reactors work at over 100 bar pressure, which can lead to devastating steam explosions if the coolant is lost.

Due to the chemical reactivity of sodium, many fission products are bound in the event of a core meltdown, especially iodine-131.

The usual "pool design", in which the reactor core is located in a large tank full of sodium, enables passive dissipation of the residual heat in the event of an emergency shutdown due to the high heat capacity and the high boiling point of sodium. When using metallic fuels (such as the EBR-II in the Idaho National Laboratory ), the high thermal conductivity of fuel and coolant leads to a strong attenuation of the thermal output due to the Doppler effect when the temperature rises rapidly . A core meltdown in the event of a cooling failure, for example due to a power failure, is passively prevented. This has been verified experimentally at the EBR-II.

## use

Currently, the BN-600 (600 MW) and, since 2014, the BN-800 in the Belojarsk nuclear power plant are operating two breeder reactors in Russia that generate electricity (as of 2015). Plants are under construction in the People's Republic of China and India.

In Japan in 2007 - after the Monju plant was shut down - there was development work for a new commercial breeder reactor.

The first German sodium-cooled experimental reactor KNK- I (Compact Sodium-Cooled Nuclear Reactor Plant Karlsruhe) was built in the years 1971 to 1974 in the Karlsruhe Nuclear Research Center . The system was converted into a fast breeder with the designation KNK-II in 1977 and was in operation until 1991.

The Phénix nuclear reactor in France was in commercial operation between 1973 and 2010 with an electrical output of 250 MW.

From 1973 onwards, an industrial breeder reactor prototype power plant named SNR-300 was built on the Lower Rhine near Kalkar . After numerous protests and the Chernobyl reactor accident in 1986 , the commissioning or even the generation of electricity, which was planned for 1987, never came about.

Some breeder reactor demonstration plants, e.g. For example, the Creys-Malville (Superphénix) nuclear power plant in France and Monju in Japan were finally shut down due to incidents (largely caused by sodium-related corrosion problems, leaks due to high coolant temperatures, etc.) and resistance among the population. However, like the abandonment of the German-Belgian-Dutch breeder reactor project in Kalkar, this is partly due to the fact that with the uranium supply situation up to now there is no economic pressure to introduce this more expensive variant of nuclear energy generation.

In India , the PFBR is scheduled to go into operation in 2020 , with a capacity of 500 MW, which contains thorium instead of depleted uranium in the breeding mantle. India has the largest supplies of thorium in the world and is a pioneer in this technology.

## Examples of breeder reactors

business country place Surname electr. Power
in MW
comment
from to
1946 1952 United States New Mexico Clementine 0.025 First breeder reactor, served as a neutron source for research for 6 years
1951 1964 United States Idaho EWC-I 0.2 Second breeder reactor, supplied the first nuclear-generated electrical energy (also Chicago Pile 4), partial meltdown 1955 (INES: 4)
1961 1964 United States New Mexico LAMPRE Melt of plutonium and iron as fission and breeding material with sodium as a coolant
1961 1994 United States Idaho EWC II 20th
1962 1977 Great Britain Dounreay DFR 14th
1963 1972 United States Detroit FERMI 1 61 Investigation of economic efficiency, partial meltdown in 1966 ( INES : 4), shutdown due to problems in 1972
1967 1983 France Cadarache Rapsody 40 Test reactor
1973 1999 Kazakhstan Aqtau BN-350 150 First breeder reactor of the Russian BN series
1974 2010 France Marcoule ( Gard ) Phénix 250 Officially shut down on February 1, 2010
1974 1994 Great Britain Dounreay PFR 250
1977 1991 Germany Karlsruhe KNK I + II 20th Test reactor
1978 Japan Joyo 100 Research reactor
1980 1992 United States Washington FFTF 400 Experimental reactor, switched off in hot standby in 1992 and has been dismantled since 2002
1980 today Russia Beloyarsk 3 BN-600 600 Since the shutdown of Creys-Malville in 1996 and the commissioning of Belojarsk 4 in 2014, the world's largest breeder; no containment
1985 today India Kalpakkam FBTR 13 Test reactor, thermal output 40 MW
1986 1996 France Creys-Mépieu Superphénix 1180 Removed from the network in 1996 after incidents ( INES : 2), finally shut down after a government decision in 1998 for cost reasons, since 2006 in dismantling.
1994 2017 Japan Fukui Monju 280 After a serious incident in 1995, test operations were resumed on May 6, 2010, but have since been terminated as a result of further incidents.
- - Germany Kalkar SNR-300 327 Construction work stopped in 1991, was never put into operation
2010 today People's Republic of China CIAE near Beijing CEFR 20th "China Experimental Fast Reactor", test reactor, in operation since July 21, 2010
2014 India Kalpakkam PFBR 500 Prototype / demonstration reactor, conversion of thorium into U-233, commissioning planned for 2015, according to the current status (Nov. 2018) but still under construction
2014 today Russia Beloyarsk 4 BN-800 800 Productive reactor, critical since June 2014, in operation from 2015
[2023] People's Republic of China Xiapu-1 CFR-600 "China Demonstration Fast Reactor", planned for 2023

## literature

• AM Judd: Fast Breeder Reactors . Pergamon Press, 1981, ISBN 0-08-023220-5 .
• Günther Kessler: Nuclear Fission Reactors: Potential Role and Risks of Converters and Breeders . Springer Wien, Vienna 2013, ISBN 978-3-7091-7624-5 .

Wiktionary: breeder reactor  - explanations of meanings, word origins, synonyms, translations

## Individual evidence

1. Fast Neutron Reactors . World Nuclear Association website. Retrieved July 17, 2015. (English)
2. W. Marth: On the history of the fast breeder project . Nuclear Research Center Karlsruhe, report KfK-3111 (1981).
3. Cornelis H. Broeders: Development work for the neutron physical design of advanced pressurized water reactors (FDWR) with compact triangular lattices in hexagonal fuel elements. Nuclear Research Center Karlsruhe, report KfK-5072, 1992.
4. Claus Petersen: Literature overview of mechanical and physical properties of cladding tube materials for advanced pressurized water reactors (FDWR) at high temperature. Nuclear Research Center Karlsruhe, report KfK-3469 (1983).
5. J. Yamashita, F. Kawamura, T. Mochida: Next-generation Nuclear Reactor Systems for Future Energy. ( PDF ; 174 kB). In: Hitachi Review. 53, 2004, pp. 131-135.
6. The technical term in nuclear technology is split , not split .
7. Erich Übelacker: WHAT IS WHAT. Volume 3: Atomic Energy. Tessloff Verlag, Nuremberg 1995, ISBN 3-7886-0243-0 , p. 29.
8. Merle E Bunker: Early Reactors From Fermi's Water Boiler to Novel Power Prototypes. In: Los Alamos Science Report. 1983. library.lanl.gov
9. AM Judd: Fast Breeder Reactors . Pergamon Press, 1981, ISBN 0-08-023220-5 , p. 3.
10. Florian Grenz: Seminar on Energy and Society. Topic: Nuclear energy (PDF, 1.1 MB), p. 8.
11. Information group KernEnergie Nuclear Energy Basic Knowledge ( Memento from June 17, 2012 in the Internet Archive ) (PDF, 11.1 MB), p. 54.
12. ^ Friedhelm Noack: Introduction to electrical energy technology - fast breeder. Hanser Verlag, 2003, ISBN 3-446-21527-1 , p. 110.
13. Nuclear Engineering Division, "Passively safe reactors rely on nature to keep them cool", reprint of the Argonne Logos magazine - (Winter 2002 - vol. 20, no. 1) [1] 1
14. Handelsblatt: Japan has a new breeder reactor developed .
15. Mitsubishi Heavy Industries website, accessed January 2020
16. W. Marth: The fast breeder SNR 300 in the ups and downs of its history . Nuclear Research Center Karlsruhe, report KfK-4666, 1992.
17. ^ IAEA reactor directory ( Memento from May 9, 2003 in the Internet Archive )
18. Performance data in the IAEA's Power Reactor Information System (English)
19. ^ Nuclear Engineering International: Criticality for China's first fast reactor. ( Memento from September 6, 2012 in the web archive archive.today ) (July 23, 2010)
20. ^ The Hindu: Nuclear Plant near Chennai All Set for Milestone
21. Kalpakkam fast breeder reactor may achieve criticality in 2019
22. freiraum-magazin.com ( Memento from January 5, 2016 in the Internet Archive )
23. World Nuclear News: China begins building pilot fast reactor ( Memento from February 4, 2018 in the Internet Archive ) (December 29, 2017)