Which one of the following is heavy water used in nuclear reactor ?

Heavy water, chemically known as deuterium oxide (D2O), is a form of water where the common hydrogen atoms (protium) are replaced by deuterium isotopes [t1][t5]. While ordinary water (H2O) has a molecular weight of approximately 18 amu (2x1 for hydrogen + 16 for oxygen), heavy water has a molecular weight of approximately 20 amu [t4][t6]. This is because deuterium contains one proton and one neutron, giving it an atomic mass of approximately 2, leading to a total molecular mass of 20.03 amu for D2O [t4][t7]. In nuclear reactors, specifically Pressurized Heavy Water Reactors (PHWRs), heavy water is used as an efficient moderator to slow down fast-moving neutrons to facilitate the fission of uranium atoms [t1][t2]. It also serves as a coolant due to its stable nuclear properties [t2].

Sources

1. [2] https://hwb.gov.in/frequently-asked-questions-faqs
2. [3] https://www.britannica.com/science/heavy-water
3. [4] https://webbook.nist.gov/cgi/cbook.cgi?ID=C7789200