Heavy water production is one of the most sophisticated technologies in the world and is used in biology, physics, treatment of incurable diseases, nuclear medicine, production of radiopharmaceuticals, industrial radioisotopes and in various nuclear reactors as neutron moderator. As Tehran Research Reactor (TRR) was reaching the last stop, the construction of a heavy water production complex in the northwest of Arak began on July 26, 1998 in order to produce the heavy water required by the Bushehr Nuclear Power Plant and its other common uses. And after eight years, it was put into operation on August 26, 2006. With the design, construction, operation and indigenizing of heavy water production technology, Iran became the ninth largest producer of heavy water in the world.