Apsara, the first nuclear research reactor in Asia, became critical in 1956 at which place?

The correct answer is A, Tarapur. The Tarapur Atomic Power Station in Maharashtra was commissioned in 1969 with American assistance and was the first nuclear power station in India as well as in Asia; its first two units are boiling water reactors, a design used nowhere else in the country. Option B is wrong because Kudankulam in Tamil Nadu is the newest of the large stations and uses Russian pressurised water reactors of the VVER type. Option C is wrong because Kaiga in Karnataka came much later and uses indigenous pressurised heavy water reactors. Option D is wrong because Rawatbhata in Rajasthan, built with Canadian collaboration, was the second station and is important for a different reason, being the first to use the pressurised heavy water reactor that India later built on its own. Remember Tarapur for the first station and Rawatbhata for the first heavy water reactor.

The correct answer is A, heavy water. The CANDU design, from which India's pressurised heavy water reactors descend, burns natural uranium, and natural uranium contains only about seven parts in a thousand of the fissile isotope uranium 235. Such a lean fuel can sustain a chain reaction only if very few neutrons are wasted, and heavy water absorbs far fewer neutrons than ordinary water while still slowing them down, so it serves as both moderator and coolant. Option B is wrong because light water absorbs too many neutrons, which is why reactors that use it must be fuelled with enriched uranium. Option C is wrong because carbon dioxide is used as a coolant in gas cooled reactors, where graphite is the moderator. Option D is wrong because liquid sodium is the coolant of a fast breeder reactor, which deliberately has no moderator at all.

The correct answer is C, a mixture of water and steam. In a boiling water reactor, the design used at Tarapur, ordinary water is allowed to boil inside the reactor vessel itself, so the coolant leaving the core is a mixture of water and steam; the steam is separated at the top and driven straight to the turbine, without the separate steam generator that other designs need. Option A is wrong because carbon dioxide cools gas cooled reactors, not water reactors. Option B is wrong because pressurised water is the coolant of the pressurised water reactor, where the pressure is kept high precisely so that the water does not boil, which is the difference between the two designs. Option D is wrong because liquid metal, usually sodium, cools a fast breeder reactor. The single fact to carry into the hall is that boiling water reactors boil the water in the core and pressurised reactors do not.

The correct answer is B, Homi Jehangir Bhabha. Bhabha founded the Tata Institute of Fundamental Research in 1945, became the first chairman of the Atomic Energy Commission in 1948, drew up the three stage plan built around India's thorium, and led the establishment at Trombay that was renamed the Bhabha Atomic Research Centre after his death in 1966. Option A is wrong because Vikram Sarabhai is the father of the Indian space programme, although he did chair the Atomic Energy Commission after Bhabha. Option C is wrong because Raja Ramanna led the team that carried out the Pokhran test of 1974, an important role but a later one. Option D is wrong because A. P. J. Abdul Kalam is associated with missile development and with the Pokhran tests of 1998. Bhabha for atomic energy and Sarabhai for space is the pair to fix.

The correct answer is B, fast breeder reactors. The second stage uses the plutonium 239 recovered from the spent fuel of the first stage as the fuel of a fast breeder reactor, with a blanket of thorium around the core that is converted into uranium 233; a breeder produces more fissile material than it burns, which is how the programme builds up a stock of fuel for the third stage. Option A is wrong because pressurised heavy water reactors burning natural uranium make up the first stage. Option C is wrong because boiling water reactors were imported for Tarapur and were never part of the staged plan. Option D is wrong because gas cooled reactors have no place in the Indian programme at all. Learn the chain in order: natural uranium, then plutonium with a thorium blanket, then uranium 233 from thorium.