India is estimated to have an arsenal of 90–110 nuclear weapons. This figure is based on calculations of India’s inventory of weapon-grade plutonium and the number of operational nuclear-capable delivery systems.
India’s nuclear weapons are believed to be plutonium-based. As of 2015 India’s weapon-grade plutonium stockpile was estimated to be between 0.57 and 0.61 tonnes The plutonium was produced at the Bhabha Atomic Research Centre (BARC) by the 40 megawatt-thermal (MW(t)) heavy water CIRUS reactor, which was shut down at the end of 2010, and the 100- MW(t) Dhruva heavy water reactor.
India has plans to build six fast breeder reactors, which will significantly increase its capacity to produce plutonium for weapons. A 500 megawatt-electric (MW(e)) prototype fast breeder reactor (PFBR) is being built at the Indira Gandhi Centre for Atomic Research (IGCAR) complex at Kalpakkam, Tamil Nadu. It is expected to achieve first criticality during 2015, to be followed by an extended period of testing.