Nuclear reactor for std 11 & 12 GSEB course Chemistry

A nuclear reactor is a device which controls the nuclear fission chain reaction to harness nuclear energy for peaceful purposes. A nuclear reactor which is used to generate electricity, is called a nuclear power plant. 

Nuclear power plant :
In a nuclear power plant, the energy released by fission is used to produce superheated steam. This turns a turbine which intern operates an electric generator. A nuclear power plant has the following components. (a) The fissionable material or nuclear fuel (b) the moderator (c) the control rods (d) the pressure vessel (steel vessel) (e) a cooling system with pump and (f) a heat exchanger.

A nuclear power plant has the following components.
(a)The fissionable material or nuclear fuel
(b)the moderator
(c)the control rods
(d)the pressure vessel (steel vessel)
(e)a cooling system with pump and
(f)a heat exchanger.

Nuclear Reactor  (Chemistry)

In a nuclear power plant nuclear fuel in the form of pellets are enclosed in several tubular claddings of steel or aluminium. This is called fuel assemble. Enriched U-235 or Pu-239 is the fuel material. The fast neutrons released during fission are slowed down by moderator, usually graphite surrounding the fuel assembly. A coolant is circulated through the reactor to remove the heat generated. Ordinary water is most commonly used coolant. Other coolants such as heavy water, Liquid sodium, molten salts and hydro carbon liquids are also used.

Road made of boron or cadmium which are neutron absorbers are used as control roads. The neutrons available for fission are controlled by moving the control rods in and out of the nuclear core. The rods can be used to shut down the reactor. Functioning of the reactor is constantly monitored with the help of suitable instruments.
Heat produced during fission process is absorbed by the coolant and is used to convert water into steam in the heat exchanger. The steam is used to generate electricity.
The entire reactor is enclosed in a concrete building with lead sheets covered inside to prevent radioactive radiations being released into the environment. 

Note this
·Enrichment means increasing the abundance.
·Heavy water – chemical name is deuterium oxide.
·In modren fast reactors there is no need for moderator.

Note this
Radiation emitted by the large amount of radioactive material is absorbed by thick concrete shields. If cooling system fails. melt down of the core may occur.

RADIATION HAZARDS
Radiations consist of a– particles, b- rays, g- radiations, x-rays and ultraviolet rays. Radiations also include protons, neutrons and other subatomic particles All these radiations are dangerous to human health and environment.
The gamma radiation is the most dangerous because of its high penetrating power and high energy. x – rays can cause a similar damage.
High frequency radiations and rays consisting of charged particles cause ionisation of atoms and molecules. The ions formed can damage DNA molecule. This may lead to genetic disorder and defective off springs, leukaemia and cancer of various types.
Visible light in the form of high power laser beam can inflict damage. Even microwaves cause damage. Ultraviolet rays cause skin burns, premature cataract and even skin cancer.
Intense radiations alter the properties of metals and structure of materials. This weakens the strength of materials.
Radioactive radiations from nuclear installations affect environment and is hazardous. The fall our of a nuclear explosion is more hazardous.

POINTS TO REMEMBER
(1) Energy released released during nuclear reaction is called nuclear energy.
(2) Any reaction that involves a change in the nucleus of an atom is called a nuclear reaction.
(3) Minimum energy required to separate the nucleons of an atom or the energy that binds the nucleus of an atom is called binding energy.
(4) According to Einstein, mass and energy are interconvertable under certain circumstances. Mass and Energy relation is represented by E=mc2.
(5) Mass defect is the difference between mass of the material before the nuclear reaction and total mass of the products after the reaction.
(6) The reaction in which a heavy nucleus splits up into two lighter nuclei with the liberation of enormous amount of energy is called nuclear fission.
(7) Chain reaction is a continuous nuclear fission reaction.
(8) Controlled chain reaction is a principle of a nuclear reactor.
(9) Uncontrolled chain reaction is a principle of nuclear bomb.
(10) The minimum size of a fissionable material required to sustain fission chain reaction is called critical size.
(11) A device which converts unclear energy into electrical energy is called nuclear reactor.
(12) Fissionable material used in India nuclear reactors is enriched uranium. (U-235) and plutonium-239.
(13)The entire reactor is enclosed in a concrete building with lead sheets covered inside to prevent radioactive radiations being radiations being released into the environment.
(14) The reaction in which two or more light nuclei combine to form a heavier nucleus with the liberation of enormous amount of energy is called unclear fusion reaction.
(15) Nuclear fusion reaction is safer than nuclear fission reaction.
(16) Radioactive radiations from nuclear installations effect environment which is hazardous. The worst amongst them is the genetic damage/disorder.