The light water reactor (LWR) is a nuclear reactor which employs ordinary water as coolant and neutron moderator instead of heavy water (deuterium/tritium). In the Western hemisphere, two main types have been used: the pressurized water reactor (PWR) and the boiling water reactor (BWR). In the former type, the water is pressurized in a vessel that contains the core and the core barrel, with the light water being at a sufficiently pressure to avoid boiling; while in the latter type (BWR), there is a boiling of water that occurs within the core, then it is dried in moisture separator to become steam that flows to the turbine.
Light water reactors use either conventional uranium fuel cycle or MOX, which is a blend of plutonium and uranium dioxide. In the MOX fuel cycle, plutonium oxide is mixed with uranium dioxide for use as fuel as it is employed mainly in Japan, France, and Germany. It was first used in Europe and the USA in the mid 1960s. The success of burning plutonium in MOX fuel proves that plutonium is an asset which can be employed in civil for AC power generation. Large-scale recycling plutonium facilities have been developed in France, with safe operation. “MOX” derives from Mixed Oxides.
A light water reactor is the most widely operating type of reactor in the world. Thus, its fuel optimization is of the utmost importance. There is intense competition between fuel vendors as there are different designs which offer different performance advantages. MOX fuel, up to 30% loading, can be used in LWR within current operating and safety margins. Higher percentage loading requires control rod changes to keep current margins.
Below, diagram of a light water reactor, using the pressurized water design.
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