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A boiling water reactor (BWR) is a type of nuclear reactor used for the generation of electrical power. It is the second most common type of electricity-generating nuclear reactor after the pressurized water reactor (PWR). BWR are thermal neutron reactors, where water is thus used both as a coolant and as a moderator, slowing down
BWR designs operate constantly at about half the primary system pressure of PWR designs while producing the same quantity and quality of steam in a compact system: 1020 psi (7 MPa) reactor vessel pressure, and 288 °C temperature for BWR which is lower than 2240 psi (14.4 MPa) and 326 °C for PWR.
In modern BWR fuel bundles, there are either 91, 92, or 96 fuel rods per assembly depending on the manufacturer. A range between 368 assemblies for the smallest and 800 assemblies for the largest U.S. BWR forms the reactor core. Each BWR fuel rod is back filled with helium to a pressure of about three atmospheres (300 kPa).
A pressurized water reactor (PWR) is a type of light-water nuclear reactor. PWRs constitute the large majority of the world's nuclear power plants (with notable exceptions being the UK, Japan, India and Canada). In a PWR, water is used both as a neutron moderator and as coolant fluid for the reactor core.
The Reactor Protection System (RPS) is a system, computerized in later BWR models, that is designed to automatically, rapidly, and completely shut down and make safe the Nuclear Steam Supply System (NSSS – the reactor pressure vessel, pumps, and water/steam piping within the containment) if some event occurs that could result in the reactor entering an unsafe operating condition.
Boiling water reactors (BWR) [moderator: low-pressure water; coolant: low-pressure water] A BWR is like a PWR without the steam generator. The lower pressure of its cooling water allows it to boil inside the pressure vessel, producing the steam that runs the turbines. Unlike a PWR, there is no primary and secondary loop.
These types are not exclusive, for example a VVER is a PWR. It may not even always be clear what is included in a type: In some contexts an ABWR is a type of BWR, but in most contexts it is not. See also Category:Nuclear power stations and its subcategories for details of particular power reactors.
Slightly different versions of the ABWR are offered by GE-Hitachi, Hitachi-GE, and Toshiba. [5]In 1997 the GE-Hitachi U.S. ABWR design was certified as a final design in final form by the U.S. Nuclear Regulatory Commission, meaning that its performance, efficiency, output, and safety have already been verified, making it bureaucratically easier to build it rather than a non-certified design.