Pressurized Water Reactor

Why are there two pages, one titled pressurized water reactor (with capitalization that is in accord with the usual Wikipedia custom) and this other one, with inappropriate captial letters in the title?

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A pressurized water reactor (PWR) is a nuclear reactor that uses water for both coolant and moderator.

• Coolant. The heat generated by the fissioning of nuclear material (most notably U-235) is transferred through the fuel within the fuel rod, through the metal "cladding" that encases the fuel, and into the water that flows in channels that extend the length of the fuel assembly. That water is removed and sent to a steam generator where the heat from the reactor is transferred to secondary water that is boiled to steam for use outside of the reactor enclosure.

• Moderator. The energy of the neutrons produced in nuclear fission is too high for those neutrons to be useful in causing significant additional fissions within the reactor fuel. In a PWR, the energy of the neutrons must be reduced to "thermal" levels. "Thermal" levels are those in rough equilibrium with the temperature of the surrounding medium, that is, to something under 800 degrees Fahrenheit. This is accomplished, in the PWR, by allowing the neutrons to undergo collisions with the molecules of water in the coolant. Each collision results in a transfer of energy from the free neutron to the atoms of the water molecule. The energy of the neutron is thus reduced while the water energy (as heat) is increased. After a number of collisions (around 8 - 10 on average), the neutron energy level has reached thermal equilibrium with its surroundings and the absorption of the neutron by a Uranium atom becomes highly probable. Once that happens, fissioning results in a short time.

One of the key control mechanisms for controlling a nuclear reactor is the rate of release of neutrons in a fission event. On average, each fission releases just over two neutrons, which permits a chain reaction to be generated. If all neutrons were released instantaneously, the chain reactor would grow so rapidly that an "uncontrolled" chain reaction would ensue, resulting in the destruction of the fuel cells and a melt-down of the reactor. However, a small fraction of these neutrons are released over an extended period (extending to over a minute). This small, but crucial, release of "delayed neutrons" permits the other control mechanisms (negative temperature co-efficient, human or computer manipulation of control rods, etc.) to have an effect.