Fast breeders use fast neutrons to convert the stable nuclei of U338 and Thorium to fissile nuclei. The fast neutrons come from the fission of uranium 235 or plutonium. Fissile fuel is bred from fertile nuclei.
Breeders were developed because it was thought there was a shortage of uranium. .
A normal reactor uses water between the fuel rods to slow down the neutrons allowing them to be captured by U235 making it unstable. It breaks apart, or fissions, giving off fast neutrons that slow down in water producing heat. The remnants are daughter atoms, and many of these fission also. However some of these waste products absorb neutrons and slow down, or poison the fission process. So the fuel must be disposed of when only 0.65% of it has been used.
Breeders can prevent this build up of nuclear waste, and/or burn it up.
By using molten metal such as sodium or lead as a coolant, the neutrons are not slowed down. Fast neutrons can be captured by fertile atoms such as U238 or Thorium 232. These neutrons turn fertile atoms into fissile atoms. Slow neutrons cannot make any nuclei fissile if it has an even number of neutrons. Fast neutrons can, so atoms that are normally wasted can be made to fission, producing energy.
The advantage of this is that instead of 0.65% of the Uranium being used, 99.5% is. The long lived waste that can become such a problem, is converted to energy and short lived waste.
By changing the material used in the blankets (walls), the breeder can be operated over a spectrum from breeder to burner. In breeder mode it uses U-238 or thorium blankets to absorb neutrons. it will produce more fissile material than it consumes. This is useful for providing fissile material for starting up other plants. Using steel reflectors instead of U-238 blankets, the reactor operates in pure burner mode and is not a net creator of fissile material; on balance it will consume fissile and fertile material.
There are no commercial breeders in production. (2012)
Research on all nuclear power in USA was canceled in 1994 due to public protests.
It is not easy for anyone to tell if the breeder reactor is the answer to our dreams, or the beginning of a never ending nightmare.
The temperature of a neutron gives the speed and energy measured in electron Volts eV.
The problem with a fast breeder
The main technical and economic challenge of a breeder using thorium is the improvement of the reactor’s neutron budget. The fission process produces a little over two neutrons per neutron absorbed. One is needed for the next cycle of fission, and in the case of breeding, at least one other neutron must be absorbed by the fertile thorium. This leaves only a small fraction of neutrons to be lost to neutron-absorbing fission products. Hence a breeder must rapidly and continuously remove any neutron-absorbing fission products from the fuel salt. It is this demanding continuous processing of the fuel salt which represents the single largest technological hurdle.
By dissolving the Uranium fluoride in molten salt, it is much easier to process than solid fuels. This is the MSR or Molten Salt Reactor. (Next page)
Some notes on fast breeder reactors
There are two ways to breed fissile nuclear fuel from Fertile material: Fast breeding or Thermal breeding
If you have U-238 (Natural or Depleted Uranium), the the nuclear cross-section requires the neutron speed to reliably be above a certain speed to breed.
If the fertile material is Thorium, then either the Thermal or Fast spectrums are possible.
(a) If you fast breed lots of Plutonium from Uranium 238 then you have feedstock for a nuclear weapon (eg Little Boy through to W88 Trident II SLBM)
(b) If you thermally breed lots of Uranium 233 from Thorium then you have lots of HEU (Highly enriched uranium) feedstock for a nuclear weapon (eg Operation Teapot).
However, if you mix Thorium AND a small amount of Uranium-238, then THERMAL breeding is still at or above "break-even", and you can not use the resultant Uranium mix any time to make a nuclear weapon, without an enrichment plant. Thermal breeding also produces a lot of heat, so you can make electricity from hot water or hot gas.
So a U-238 Fast Breeder reactor, is a danger for nuclear proliferation.
Now, the most effective Fast Breeder reactor is the Liquid Sodium Fast Breeder Reactor, and has been actually built in various experiments.
If liquid sodium is exposed to water or humid air it produces hydrogen which explodes. If exposed to air it ignites.
The safety issues surrounding a Liquid Sodium Fast Breeder Reactor are worse then existing Water based converter reactors.
Fast reactors in India
India’s Department of Atomic Energy has always promised much and delivered little. In the early 1970s, for example, DAE projected that by 2000 there would be 43,000 MW of installed nuclear capacity. In 2000, that capacity was actually 2,720 MW. Today, nuclear power constitutes barely 2 per cent of the total electricity generation capacity.
India has been developing a long-term three stage nuclear fuel cycle to utilise its abundant thorium resources. The construction of a 500 megawatt electric (MWe) prototype fast breeder reactor at Kalpakkam, near Madras, was about 94% complete in February 2013. It will have a blanket with thorium and uranium to breed fissile 233U and plutonium respectively. Six more such fast breeder reactors have been announced for construction and this project will take India's thorium program to stage 2. Source
Summary of nuclear energy - http://www.energy-without-carbon.org/NuclearSummary
Radio active decay - http://www.energy-without-carbon.org/RadioActiveDecay
Nuclear fusion - http://www.energy-without-carbon.org/NuclearFusion
Engel, J.R., et.al, (1980 July) "Conceptual Design Characteristics of a Denatured Molten Salt Reactor", ORNL/TM-7207
OECD Nuclear Energy Agency's open tool JANIS (Java Nuclear Information System):