I think you are talking about nuclear reactors. PWR is a Pressurized Water Reactor, and is the basis for most power generators. BWR is a Boiling Water Reactor. As the water is a major moderating component, controlling the speed and intensity of the nuclear reaction, the steam bubbles in a BWR can present a problem.
PWR stands for Pressurized Water Reactor, which uses pressurized water to transfer heat from the reactor core to the steam generators to produce electricity. BWR stands for Boiling Water Reactor, which directly produces steam in the reactor core to drive the turbines and generate electricity. Both are types of nuclear reactors used for power generation.
The primary difference between a pressurized water reactor (PWR) and a boiling water reactor (BWR) is that in the BWR, water is actually boiled, and the steam is used to drive a steam turbine, while in the PWR, the primary coolant is not allowed to boil, but is circulated in a closed loop to boil water in a steam generator. The BWR circulates primary coolant through the steam turbine in a closed loop. The PWR contains the primary coolant in a loop that includes the steam generator, and not the steam turbine.
BWR = Boiling Water Reactor. In this type a certain proportion of the reactor coolant water is allowed to turn to steam (unlike in a PWR), this steam is separated out from the water after the reactor outlet and passes directly to the steam turbine.
The abbreviation for the word power is "PWR."
Fuel elements for PWR and BWR are described here (from Wikipedia) There is a picture shown but pictures don't reproduce on Wikianswers. Pressurized water reactor (PWR) fuel consists of cylindrical rods put into bundles. A uranium oxide ceramic is formed into pellets and inserted into Zircaloy tubes that are bundled together. The Zircaloy tubes are about 1 cm in diameter, and the fuel cladding gap is filled with helium gas to improve the conduction of heat from the fuel to the cladding. There are about 179-264 fuel rods per fuel bundle and about 121 to 193 fuel bundles are loaded into a reactor core. Generally, the fuel bundles consist of fuel rods bundled 14x14 to 17x17. PWR fuel bundles are about 4 meters in length. In PWR fuel bundles, control rods are inserted through the top directly into the fuel bundle. The fuel bundles usually are enriched several percent in 235U. The uranium oxide is dried before inserting into the tubes to try to eliminate moisture in the ceramic fuel that can lead to corrosion and hydrogen embrittlement. The Zircaloy tubes are pressurized with helium to try to minimize pellet cladding interaction (PCI) which can lead to fuel rod failure over long periods. In boiling water reactors (BWR), the fuel is similar to PWR fuel except that the bundles are "canned"; that is, there is a thin tube surrounding each bundle. This is primarily done to prevent local density variations from effecting neutronics and thermal hydraulics of the nuclear core on a global scale. 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 nuclear power reactor, mainly PWR and BWR types.
In the operation of nuclear power plants like PWR and BWR
PWR and BWR reactor types. Look up in Wikipedia.
Reactors of the BWR and PWR types
In the operation of nuclear power plants like PWR and BWR
PWR stands for Pressurized Water Reactor, which uses pressurized water to transfer heat from the reactor core to the steam generators to produce electricity. BWR stands for Boiling Water Reactor, which directly produces steam in the reactor core to drive the turbines and generate electricity. Both are types of nuclear reactors used for power generation.
Nuclear power plants (BWR, PWR, AGR, etc.)
All power producing reactors are either PWR or BWR types
The primary difference between a pressurized water reactor (PWR) and a boiling water reactor (BWR) is that in the BWR, water is actually boiled, and the steam is used to drive a steam turbine, while in the PWR, the primary coolant is not allowed to boil, but is circulated in a closed loop to boil water in a steam generator. The BWR circulates primary coolant through the steam turbine in a closed loop. The PWR contains the primary coolant in a loop that includes the steam generator, and not the steam turbine.
Mostly in reactors fuelled by Uranium and moderated and cooled by light water (PWR and BWR types)
At present only nuclear fission can be used, in various types of reactor. The PWR and BWR are the most commonly used.
In a nuclear reactor the nuclear energy released by fission appears as heat in the fuel rods, which is then transferred to the reactor coolant (ie water in PWR and BWR)