ReactorSystem used to initiate, maintain and control a fission chai... cooled and/or moderated with heavy waterDeuterium oxide, D2O; water containing two deuterium atoms i... (D2O). Example: CANDUCanadian heavy-water-moderated pressure tube natural uranium... reactors; D2O pressurized water reactorPower reactor in which the heat is dissipated from the core ... Atucha, Argentina.