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05/01/2006 10:19 AM LWRs, which are the most commonly deployed power generating reactors in the world, and supercritical fossil fuel fired boilers, a large number of which are also in use around the world. The SCWR concept is being investigated by 32 organizations in 13 countries. Molten Salt Reactor (MSR) A molten salt reactor is a type of nuclear reactor where the working fluid is a molten salt. There have been many designs put forward for this type of reactor and a few prototypes built. The early concepts and many current ones had the nuclear fuel dissolved in the molten fluoride salt working fluid as uranium tetrafluoride (UF4), the fluid would reach criticallity by flowing into a graphite core which also served as the moderator. Many current concepts rely on fuel that is dispersed in a graphite matrix with the molten salt providing low pressure, high temperature cooling. Gas-Cooled Fast Reactor (GFR) The Gas-Cooled Fast Reactor (GFR) system features a fast-neutron spectrum and closed fuel cycle for efficient conversion of fertile uranium and management of actinides. The reactor is helium-cooled, with an outlet temperature of 850°C and using a direct Brayton cycle gas turbine for high thermal efficiency. Several fuel forms are being considered for their potential to operate at very high temperatures and to ensure an excellent retention of fission products: composite ceramic fuel, advanced fuel particles, or ceramic clad elements of actinide compounds. Core configurations are being considered based on pin- or plate-based fuel assemblies or prismatic blocks. Sodium-Cooled Fast Reactor The SFR is a project that builds on two closely related existing projects, the LMFBR and the Integral Fast Reactor. The goals are to increase the efficiency of uranium usage by breeding plutonium and eliminating the need for transuranic isotopes ever to leave the site. The reactor design uses ‘ an unmoderated core running on fast 1 ! neutrons, designed to allow any transuranic Sodium-Cooled Fast Reactor isotope to be consumed (and in some cases (SFR) used as fuel). In addition to the benefits of removing the long half-life transuranics from the waste cycle, the SFR fuel expands when the reactor overheats, and the chain reaction automatically slows down. In this manner, it is passively safe. Page 3 of 5 Generation IV reactor - Wikipedia, the free encyclopedia Molten Salt Reactor (MSR) Main article: Molten salt reactor Fast reactors Gas-Cooled Fast Reactor (GFR) Main article: Gas cooled fast reactor Sodium-Cooled Fast Reactor (SFR) Liquid Metal Fast Breeder Reactor (LMFBR) Main article: LVFBR Integral Fast Reactor (IFR) http://en.wikipedia.org/wiki/Generation_IV_reactor