In which year was the CIRUS reactor (second Indian reactor) established and what fuel did it use?

The correct answer is Option B — 1960 and Natural Uranium. CIRUS (Canada India Reactor Utility Services) was established in 1960 at BARC Mumbai with Canadian assistance. It used natural uranium as fuel and heavy water (D2O) as moderator. CIRUS had a thermal power of 40 MW and played a crucial role in India's nuclear research including production of plutonium used in India's first nuclear test in 1974. Option A is incorrect: 1956 and enriched uranium describes Apsara reactor which was India's first reactor not CIRUS. CIRUS used natural uranium not enriched uranium. Option C is incorrect: 1972 and plutonium oxide describes Purnima-1 reactor which was India's third major reactor. It was India's first fast neutron reactor. Option D is incorrect: 1985 and natural uranium describes Dhruva reactor which is India's largest research reactor. Dhruva also uses heavy water as moderator but was established 25 years after CIRUS.