Fast Breeder Reactor
Figure shows a fast breeder reactor system. In this reactor the core containing U235 in surrounded by a blanket (a layer of fertile material placed outside the core) of fertile material U238. In this reactor no moderator is used. The fast moving neutrons liberated due to fission of U235 are absorbed by U238 which gets converted into fissionable material Pu239 which is capable of sustaining chain reaction. Thus this reactor is important because it breeds fissionable material from fertile material U238 available in large quantities. Like sodium graphite nuclear reactor this reactor also uses two liquid metal coolant circuits. Liquid sodium is used as primary coolant when circulated through the tubes of intermediate heat exchange transfers its heat to secondary coolant sodium potassium alloy. The secondary coolant while flowing through the tubes of steam generator transfers its heat to feed water.
Fast breeder reactors are better than conventional reactors both from the point of view of safety and thermal efficiency. For India which already is fast advancing towards self reliance in the field of nuclear power technology, the fast breeder reactor becomes inescapable in view of the massive reserves of thorium and the finite limits of its uranium resources. The research and development efforts in the fast breeder reactor technology will have to be stepped up considerably if nuclear power generation is to make any impact on the country’stotal energy needs in the not too distant future.
Figure: Fast breeder reactor.
Coolants are used for Fast Breeder Reactors
The commonly used coolants for fast breeder reactors are as follows:
i) Liquid metal (Na or NaK).
ii) Helium (He)
iii) carbon dioxide.
Sodium has the following advantages:
i) It has very low absorption cross-sectional area.
ii) It possesses good heat transfer properties at high temperature and low pressure.
iii) It does not react on any of the structural materials used in primary circuits.