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NUCLEAR REACTOR – MAIN PARTS AND THEIR FUNCTIONS: Contd^ ^ Control Rods^ •^ Control rods are meant for controlling the rate of fission of U-235.^ •^ The control rods are made of boron-10, cadmium or hafnium,that absorbs some of the slowed neutrons.^ •^ In a nuclear reactor, nuclear chain rection has to be initiatedwhen started from cold, and the chain reactions is to bemaintained at a steady value during the operation of reactor.Also the reactor must be able to shut down automaticallyunder emergency conditions.
NUCLEAR POWER PLANTS
NUCLEAR REACTOR – MAIN PARTS AND THEIR FUNCTIONS: Contd^ ^ Control Rods: Contd^ •^ All this requires a control of reactor so as to prevent melting offuel rods, disintegration of coolant and destruction of reactoras the amount of energy released is enormous.^ •^ Chain reaction is controlled either by removing the fuel rods orby inserting neutron absorbing materials. The material used forcontrol rods must have very high absorption capacity forneutrons.^ •^ The control rods are inserted into the reactor core from the topof the reactor vessel. These rods regulate the fissioning in thereactor by absorbing the excess neutrons
NUCLEAR POWER PLANTS
NUCLEAR REACTOR – MAIN PARTS AND THEIR FUNCTIONS: Contd ^ Coolant: Contd •^ Coolant flows through and around the reactor core. It performsthe additional function of keeping the interior of the reactor at thedesired temperature. •^ Sometimes, the same medium is used as the coolant as well as themoderator though separate materials are used more commonly. •^ A good coolant should not absorb neutrons, should be non-oxidising, non-toxic, non-corrosive and have high chemical andradiation stability and good heat transfer capability.
NUCLEAR POWER PLANTS
NUCLEAR REACTOR – MAIN PARTS AND THEIR FUNCTIONS: Contd^ ^ Coolant: Contd^ •^ Air, helium, hydrogen and
amongst the gases, light andଶ^ heavy water amongst the liquid, and molten sodium andlithium amongst the metals are the materials used as coolants. • Ordinary water is used both as coolant and moderator inboiling water reactors and pressurized water is used both ascoolant and moderator in pressurized water reactors. • Water has good thermal capacity per unit volume
and is,
therefore, a good heat transport medium.
NUCLEAR POWER PLANTS
