Zirconium minerals contain 0.5 to 2 percent hafnium which is a strong absorber of neutrons and must therefore be removed. The main use of zirconium is for cladding fuel elements and for structural components in water-cooled systems. So it must have increased corrosion resistance. Zircaloy-2 containing 1.5% Zn , 0.1 % Fe , 0.05 % Ni and 0.1 % Cr provides better corrosion resistance and is generally used in water-cooled reactors. Zirconium has a relatively poor resistance to Co2 at elevated temperatures, but this is improved by the addition of 0.5 % Cu , 0.5% Mo with an increase of tensile strength to 51 kg-f / mm2. (510 M pa) and improved creep resistance at 450*C. This zirconium is especially useful in gas cooled reactors. The melting point of Zirconium is 1750*C.
Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movement of the
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