Process

____he CANDU reactor uses two key substances, deuterium
____oxide, also known as heavy water, as the coolant and uranium as the fuel (CANDU, nd). According to Whitlock (2007), unlike light water, H₂O, deuterium oxide replaces the hydrogen atom with heavy hydrogen, or deuterium, to become D₂O (Whitlock, 2007). The reason heavy water is used is because it is eight times worse than light water at slowing down neutrons, and absorbs 600 times less than light water (Whitlock, 2007). This key difference allows CANDU to use natural uranium and still reach criticality (Whitlock, 2007). Since light water only allows refined uranium to reach criticality, using heavy water saves the cost of extra uranium refining (Whitlock, 2007). According to Whitlock (2007), uranium mining is done entirely in Northern Saskatchewan. The uranium is then separated from the rest of the rock and sent to a refinery to reduce the uranium to uranium trioxide to be used in the reactor (Whitlock, 2007). The uranium trioxide is than reduced to uranium dioxide, a black powder that is made into cylindrical pellets about a centimetre in diameter and length (Whitlock, 2007). These pellets are put into tubes made of zircaloy, fifty centimetres long (Whitlock, 2007). The tubes are welded shut and put into CANDU (Whitlock, 2007). A standard CANDU reactor holds thirty-seven tubes, each one weighing about twenty kilograms (Whitlock, 2007).

____n order for the nuclear reactor to work, fission must
____occur. Fission will only happen in just the right circumstances (CANDU Reactor, 2007). A calandria with horizontal tubes is filled with uranium bundles (CANDU, nd). Six to ten are switched every day (Whitlock, 2007). The calandria is then filled with heavy water (CANDU, nd). Fission releases energy is the form of heat. This heat is used to heat up more heavy water (CANDU, nd; Whitlock, 2007). The steam from the heavy water is used to heat light water which creates steam to turn electrical turbines (CANDU, nd; CANDU Reactor, 2007; Whitlock, 2007) In one to one and a half years the uranium fuel runs out and is replaced (CANDU Reactor, 2007). Used uranium is put in a tank of water which cools the fuel bundles and absorbs the radiation (CANDU Reactor, 2007). According to Whitlock (2007) two independent computers are used to control the reactor. Both run at the same time, but one is only used as a back up.

____here are a few variations of the CANDU reactor that
____range from 125 megawatts of energy to over 900 megawatts of energy (Whitlock, 2007). The differences are the fuel channels (Whitlock, 2007). The CANDU 6 version produces about 700 MWe, while the CANDU 9 produces 900 MWe (Whitlock, 2007). According to Whitlock, the AECL is working on a new Advanced CANDU Reactor, ACR, that would be smaller, more efficient, use light water and less heavy water to lower costs, use some slightly enriched uranium to extend fuel life three times, have an increased power, and be less costly to construct.