India has a three-stage nuclear programme which was envisaged by Dr Homi Bhabha in the mid 50s and is still relevant. To understand better the linkage between the three stages, one should know about the fuels. The materials that one comes across as fuels for nuclear power plants are U235, U238 and U233. Natural uranium has U238 (99.27 per cent) and U235 (0.72 per cent). Only U235 can sustain a fission chain reaction and is called fissile material. Two other fissile materials that can fuel nuclear reactors are Pu239 and U233, which are manmade. Plutonium is created when U238 is irradiated in a nuclear reactor where it absorbs neutrons and part of it is transmuted into plutonium. Similarly, U233 is created when thorium is irradiated in a nuclear reactor, where it absorbs neutrons, which transmutes a part of the thorium into U233.
With the available uranium reserves, utilizing Pressurised Heavy Water reactors (PHWR) around 10,000 MWe can be generated for 30 years. These first stage reactors will utilize the U235 portion of the fuel. Besides generating power, PHWRs will convert a part of U238 in natural uranium into Pu239, which is separated from the spent fuel in plutonium reprocessing plants and used in the next stage of reactors..India has 18 PHWRs, and several more reactors are being planned.
The second stage of Fast Breeder Reactors (FBR), are fueled by plutonium (obtained from the first stage PHWRs) The fast breeder reactors will fission Pu239 for power production and at the same time breed more plutonium from the U238.The rate of PU239 production is much higher in FBRs than PHWRs. The second stage aims at conversion of available U238 to Pu 239.The surplus plutonium from each FBR can be used to set up additional FBRs and grow the nuclear capacity in tune with India’s needs. The uranium resource position is such that with FBRs a nuclear electric base of as much as 500GWe appears technically feasible. Already a Fast Breeder Test Reactor has been set up at Kalpakkam and is operational since 1985. Based on the operational experience and related engineering development, a 500 MWe fast reactor is under construction.
Effective utilization of Th232 (3.6-lakh-tonne reserves in India) is planned in the third stage.As mentioned earlier, Th232 when irradiated in a nuclear reactor gets converted into U233, a fissile material.Consolidation and further growth of the nuclear electric base is planned to by means of thorium breeders, which will form the third stage of the programme, which is several decades away. Since utilization of thorium is unique to India, process of research and development in all areas from mining to reprocessing is under development. The third stage -use of thorium for power generation has already begun. A prototype 30 KW reactor called KAMINIutilizing the U233 obtained from irradiation of Th232 in Heavy Water reactors and subsequent reprocessing has been commissioned at Kalpakkam and effectively utilised for neutron radiography and activation analysis. Design of an advance heavy water reactor that will use both plutonium-mixed oxide as fuel and convert Th232 to U233 has been completed. It incorporates several advanced safety features, such as heat removal by natural circulation.
Nuclear reactors require higher capital investment than coal fired plants but their operating costs are lower. While we can get external aid/loans to construct coal fired plants, it is not the case with nuclear plants. The efforts of the government to have understanding with nuclear powers through various deals would go a long way in the faster implementation of new plants..
In conclusion, nuclear energy will form an important part of the energy mix in India. The Indian nuclear programme has done a good job in not only assimilating and absorbing the technology, but has reached a stage where it can design, construct and operate plants indigenously.
(Compiled by Dr. G Vaidyanathan, Visiting Professor, SRM University & Retd. Group Director, Indira Gandhi Centre for Atomic Research, Kalpakkam)