Nuclear reactors

PRESENTATION ON NUCLEAR REACTORS

1. Presentation of inorganic chemistry Submitted by: Mehlil Hafeez Submitted to: Maam Azhra Naveed Topic : Nuclear Reactors

2. NUCLEAR REACTORS: Nuclear reactor is a device to obtain the nuclear energy in a controlled nuclear fission reactions, usually used to generate power. In other words, Nuclear Reactor is an equipment for carrying out controlled nuclear fission reactions, usually used to generate power. A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions .

3. A nuclear reactor is a vessel in which a nuclear reaction is carried out and maintained. The purpose of a nuclear reactor is to generate electricity, propel submarines and large ships, district heating systems, for steam powered air craft catapult etc. Splitting of atoms produces lots of energy in the form of heat. This heat is harnessed using either water or gas and then it is used to generate steam. The generated steam is used to drive the turbines which are used to produce electricity. Nuclear reactors are used at nuclear power plants for electricity generation.

4. Principle of nuclear reactors: The principle involved in the functioning of a nuclear reactor is nuclear fission. In nuclear fission, the nucleus of a heavy element is hit by a neutron due to which it breaks into different smaller nuclei. The resulting fragments are not of the same element hence this is a process is called nuclear transmutation. The emitted neutrons may then cause new fissions, which in turn yield more neutrons, and so forth. Such a continuous self-sustaining series of fissions constitutes a fission  chain reaction . A large amount of energy is released in this process, and this energy is the basis of nuclear power systems.

5. Components of nuclear reactor: Components which are common to most types of the nuclear reactors are: Fuel Core Moderator Control Rods Coolant Pressure fuel Steam generator Containment

6. FUEL: In a conventional nuclear reactor used for power generation, the fuel is uranium oxide. The most common fuel used in nuclear reactors is Uranium. The Uranium are filled inside tubes to take shape of a rod, they are also refereed as fuel rods. If the nuclear reactor is to be operated for first time then a neutron source is needed to start the reaction. The neutron sources are usually accompanied with elements which are known to be alpha emitters. The alpha decay causes neutrons to be released from the source. When reactor is operated more than one time then enough neutrons are there to start the nuclear reaction . CORE: All reactors have a core, a central region that contains the fuel, fuel cladding, coolant, and (where separate from the latter) moderator. The fission energy in a nuclear reactor is produced in the core.

7. MODERATOR: A material that has the ability to slow down neutrons quickly and which, at the same time, has little tendency to absorb neutrons is called a moderator. When the neutrons are released from the core, they travel very fast which may lead to them causing less fission. In order to increase the rate of fission, moderators are used to slow down the neutrons so that they may cause fission. The moderator is a material which is filled throughout the reactor. This material can be water, graphite or heavy water . CONTROL ROADS: The reactor is kept under control by trusting the positions ofthe control rodswhich are inserted among the nuclear fuel elementin the reactor. These control rods are usually made out of cadmium or boron,which are highly efficientfor a neutron absorption. COOLANT: The heat generated in the core of the reactor is removed by a coolant. Water used in reactor serves both as moderator and coolant. When the nuclear fission reaction happens in the core of the reactor a lot of heat is generated. The function of a coolant is to remove this heat. The purpose of the removal of heat is to not let temperature rise so high inside the reactor that the heat melts the internals of the core and another main purpose is to transfer the heat to water to transform it into steam.

8. Pressure Vessel: It is a large robust vessel which contains the core of the reactor along with all the internals along with the coolant and its delivering mechanism . Steam Generator: Some reactors contain secondary systems in coolant delivery system such as heat exchangers wherein heat is exchanged with water which gets converted into steam. In some reactor systems the coolant circulating around the core itself gets converted into steam. The tubes delivering the coolants in such cases are quite robust. CONTAINMENT : It is a large structure generator. The containment walls are several meters thick and they are made in this way to protect from the effects of radiation in case the which contains and covers all the components of nuclear reactor and stream reactor malfunctions .

9. EXAMPLES OF NUCLEAR REACTORS: PRESSURIZED HEAVY-WATER REACTOR: A   pressurized heavy-water reactor   ( PHWR ) is a  nuclear reactor  that uses  heavy water  ( deuterium oxide  D 2 O) as its  coolant  and  neutron moderator . PHWRs frequently use  natural uranium  as fuel , but sometimes also use  very low enriched uranium . The heavy water coolant is kept under pressure to avoid boiling, allowing it to reach higher temperature (mostly) without forming steam bubbles, exactly as for  pressurized water reactor . While  heavy water  is very expensive to isolate from ordinary water (often referred to as  light water  in contrast to  heavy water ), its low absorption of neutrons greatly increases the  neutron economy  of the reactor, avoiding the need for  enriched fuel .

10. LIGHT WATER REACTOR: The light-water reactor (LWR) is a type of thermal-neutron reactor that uses normal water, as opposed to heavy water, as both its coolant and neutron moderator – furthermore a solid form of fissile elements is used as fuel. Thermal-neutron reactors are the most common type of nuclear reactor, and light-water reactors are the most common type of thermal-neutron reactor.

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