In my last post, I talked about breeder reactors in general terms. There is renewed interest in this category of reactors which can burn many kinds of fuel and can generate more fissile materials than they consume. Today I will delve a little deeper into the subcategories of breeder reactors.
There are two broad types of breeder reactors. One is designed to burn uranium fuels and transuranics, the radioactive materials heavier than uranium that are created as uranium fuel is burned. The other type is designed to burn thorium and not transuranics. There are many possible designs for breeder reactors. Light water has been used in the past as a coolant but there are designs that would use molten-salt, liquid-metal or other possible coolants.
When fissile materials are created in a operating reactor, there is also a creation of materials that absorb neutrons. This means that in order to take advantage of the breeding of new fissile materials, the spent fuel from the breeder reactor must be reprocessed. The current widely used reprocessing system is called Plutonium Uranium Extraction or PUREX. PUREX is a chemical method for separating pure plutonium or pure uranium for other materials in an ore, spent fuel or nuclear waste. Any country that has an operating PUREX facility can produce pure plutonium for nuclear weapons.
Fast breeder reactors (FBR) are called that because they rely on unmoderated neutrons that are not slowed down in the reactor. This type of breeder reactor is primarily intended to breed fissile plutonium and other transuranics as it burns uranium-235. It can also breed fissile uranium-233 from thorium. Thermal breeder reactors (TBR) on the other hand utilize moderated neutrons to breed fissile uranium-233 from thorium. Unlike the FBR, the TBR reactors cannot breed transuranics from uranium fuel. This is would be important consideration with respect to the proliferation of nuclear weapons. In addition to this benefit of TBRs, they also do not product transuranics which are the hottest, most long lasting and most dangerous components of spent nuclear fuel.
Breeder reactors are being considered for such purposes as the generation of fissile materials for extraction and uses other than fuel, long term stable operation for energy generation or burning of nuclear wastes. The economics of nuclear power is making it less desirable. The existence of huge amounts of nuclear waste and the need for a disposal system makes breeders very desirable. The production of weapons grade plutonium is a threat to the world. So, in sum, while breeder reactors are very desirable for some needs, they can be very dangerous for other reasons. In future posts, I will detail some breeder reactor designs and some problems with currently operating breeder reactors.
