Ø            Pressurised Heavy Water Reactor

In a pressurised heavy water reactor, natural nuclear fuel undergoes nuclear fission inside a bundle of pressure tubes containing heavy water for cooling.  The tube bundle is placed inside a vessel, known as calendria, containing heavy water as a moderator to maintain the nuclear fission process.  The heavy water for cooling the nuclear fuel is separated from the light water used to produce steam for the turbine-generator.  The nuclear fuel in a pressure tube can be replaced when the reactor is operating.