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Outline History Introduction Types of Nuclear Reactor Heavy Water Reactor Production of Heavy Water Properties of Heavy Water Purpose of Heavy Water Application of Heavy Water
History Who first isolated heavy water? Existence of Isotopes(Francis Aston in 1913) Rutherford suggested the existence of heavier Isotope of hydrogen Harold Clayton Urey Found existence in 1931 Urey succeeded in enriching samples of water in the heavier isotope. The next step was to isolate pure heavy water. American Scientist Gilbert Newton Lewis with his student Ronald T. MacDonald
So Lewis find out that heavy water had different properties toordinary water H2O D2OFreezing point (°C ) 0.00 3.81Density of liquid (g/cm3) 0.9999 (277 K) 1.1056 (293 K)Density of solid at m.p. 0.917 1.018(g/cm3)Temperature of maximum 3.98 11.2density (°C)pH (298K) 7.00 7.43
Introduction Heavy Water (D2O) (compound of Deuterium (D) and oxygen) This is also known as Deuterium Oxide. Deuterium (atomic mass 2) for normal hydrogen (H) [due to presence of an extra neutron in the nucleus] Heavy Water resembles in its physical and chemical properties to ordinary water. (light Water) But its nuclear properties makes it an extremely efficient material for use as moderator in a nuclear reactor.
Types of Nuclear Reactors
Heavy Water Reactor• The Heavy Water Reactor (HWR) concept allow the use of natural uranium as a fuel without the need for its enrichment, especially if uranium is available for mining or for extraction as a by product of another industry such as gold mining .• However, it needs the installation of a heavy water D2O production capability, which is a much simpler to separate the light isotopes (D from H) and the heavy isotopes (U235 from U238).• HWRs have become a significant proportion of world reactor installations, second only to the Light Water Reactors (LWRs)
The HWR concept is primarily represented by the CANDU design which is an acronym for Canada Deuterium Uranium. The CANDU system uses pressurized heavy water D2O as moderator and coolant and natural uranium as fuel in the form of uranium dioxide UO2.
Production of Heavy water The production of heavy water in significant amounts requires a technical infrastructure, but one which has similarities to ammonia production, alcohol distillation, and other common industrial processes. It is possible to take advantage of the different boiling points of heavy water (101.4 °C) and normal water (100 °C) or the difference in boiling points between deuterium (-249.7 °C) and hydrogen (-252.5 °C). However, because of the low abundance of deuterium, an enormous amount of water would have to be boiled to obtain useful amounts of deuterium. Because of the high heat of vaporization of water, this process would use enormous quantities of fuel or electricity.
Properties of Heavy Watermolecular formula 2H2O/ D2Omolar mass 20.0276 g/molexact mass 20.023118178 g/molappearance pale blue transparent liquidodor Odorlessmelting point 3.8°Cmolecular weight 20.0276 g/molvapor pressure 16.4 mm Hgrefractive index 1.328viscosity at 25°C 0.001095 Pa sspecific heat of fusion 0.3096 kj/g
Purpose of using Heavy Water in Nuclear Reactor Heavy water is used as a moderator. It is used to slow the neutrons being directed at the fissionable material, by means of the molecules of the moderator physically impacting the incoming neutrons and absorbing some of the kinetic energy they posses, thus slowing them down. The reason that the neutrons have to be slowed is that most fissionable materials are more likely to absorb thermal neutrons (2.2km/s) than fast neutrons (14,000km/s). This means that when heavy water is used as a moderator, enough neutrons get through that even with very low levels of U-235 (even the very low levels found in natural uranium), criticality can be maintained, and power is produced.
Application of Heavy Water Heavy water is used as tracer in the study of reactions occurring in living organisms and other chemical reactions. It has been used for the preparation of deuterium. Chemists can use D2O as a solvent for Nuclear Magnetic Resonance spectra.