Nuclear Energy has a huge potential to ensure long term energy security. With a view to optimally utilise limited uranium reserves and large thorium reserves in the country, the Department of Atomic Energy has adopted a three-stage nuclear power programme, based on a closed nuclear fuel cycle, for generation of nuclear power and for achieving long term energy security. The three-stage nuclear power programme, which is to be implemented sequentially, aims to multiply the domestically available fissile resources through the use of natural Uranium in Pressurised Heavy Water Reactors (first stage), followed by use of Plutonium obtained from the spent fuel of Pressurised Heavy Water Reactors in Fast Breeder Reactors, in the second stage. Large scale use of Thorium will subsequently follow making use of Uranium- 233 that will be bred in Fast Breeder Reactors, when adequate nuclear installed capacity in the country has been built.  Accordingly, the utilisation of Thorium as a practically inexhaustible energy source has been contemplated during the third stage of the Indian nuclear programme, which can be reached in future. The first stage of nuclear power programme comprising indigenous Pressurised Heavy Water Reactors (PHWRs) is in industrial domain. A Prototype Fast Breeder Reactor (PFBR) under the second stage is being commissioned by Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI) at Kalpakkam, Tamil Nadu.