Breeder reactor
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A breeder reactor is a nuclear reactor that breeds fuel by producing more fissile material than it consumes.
Production of fissile material in a reactor occurs by neutron irradiation of fertile material, particularly Uranium-238 and Thorium-232. In a breeder reactor, these materials are deliberately provided, either in the fuel or in a breeder blanket surrounding the core, or most commonly in both.
Production of fissile material takes place to some extent in the fuel of all nuclear power reactors. Towards the end of its life, a uranium (not MOX, just uranium) PWR fuel element is producing more power from the fissioning of plutonium than from the remaining uranium-235. However, in order to breed, a reactor must be specifically designed to do so.
Two types of breeder reactor have been proposed:
- The fast breeder reactor or FBR. The superior neutron economy of a fast neutron reactor makes it possible to build a reactor that, after its initial fuel charge of plutonium, requires only natural (or even depleted) uranium feedstock as input to its fuel cycle. This fuel cycle has been termed the plutonium economy.
- The thermal breeder reactor. The excellent neutron capture characteristics of fissile Uranium-233 make it possible to build a heavy water moderated reactor that, after its initial fuel charge of enriched uranium, plutonium or MOX, requires only thorium as input to its fuel cycle. Thorium-232 produces Uranium-233 after neutron capture and beta decay.
Use of a breeder reactor assumes nuclear reprocessing of the breeder blanket at least, without which the concept is meaningless. In practice, all proposed breeder reactor programs involve reprocessing of the fuel elements as well.
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The FBR
Several prototype FBRs have been built, ranging in electrical output from a few light bulbs (EBR-I, 1951) to over 1000MWe. As of 2006, the technology is not economically competitive to thermal reactor technology; but Japan, China, Korea and Russia are all committing substantial research funds to further development based on existing LMFBR designs, anticipating that rising uranium prices will change this in the long term.
Looking further ahead, three of the proposed generation IV reactor types are FBRs:
- The Gas-Cooled Fast Reactor (GFR) cooled by helium.
- The Sodium-Cooled Fast Reactor (SFR) based on the existing LMFBR and Integral Fast Reactor designs.
- The Lead-Cooled Fast Reactor (LFR) based on Soviet naval propulsion units.
As well as their thermal breeder program, India is also developing FBR technology, using both uranium and thorium feedstocks.
The thermal breeder reactor
The Advanced Heavy Water Reactor is one of the few proposed large-scale uses of thorium. As of 2006 only India is developing this technology.
India's interest is motivated by their substantial thorium reserves; Almost a third of the world's thorium reserves are in India, which in contrast has less than 1% of the world's uranium. Their stated intention is to use both fast and thermal breeder reactors to supply both their own fuel and a surplus for non-breeding thermal power reactors.
Total worldwide resources of thorium are roughly three times those of uranium, so in the extreme long term this technology may become of more general interest.
See also
External links
- India announces the ATBR design.