IEMDaily - Video Lecture Notes

Definition

Nuclear reactor

A nuclear reactor is made of fuel, moderator, control rods, coolant, pressure vessel or pressure tubes, steam generator and containment.
A nuclear reactor produces and controls the release of energy from splitting the atoms of certain elements. In a nuclear power reactor, the energy released is used as heat to make steam to generate electricity.The principles for using nuclear power to produce electricity are the same for most types of reactor. The energy released from continuous fission of the atoms of the fuel is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive the turbines which produce electricity.

Example

Substances used in nuclear reactor

Common fissionable materials used in nuclear reactor are uranium rich in isotope

U^{235}

and plutonium rich in isotope

{P u}^{239}

Definition

Multiplication factor with respect to nuclear reactions

Because of the use of moderator, it is possible that the ratio, K, of number of fission produced by a given generation of neutrons to the number of fission of the preceeding generation may be greater than one.This ratio is called the multiplication factor; it is the measure of the growth rate of the neutrons in the reactor. For K = 1, the operation of the reactor is said to be critical, which is what we wish it to be for steady power operation. If K becomes greater than one, the reaction rate and the reactor power increases exponentially. Unless the factor K is brought down very close to unity, the reactor will become supercritical and can even explode.

Definition

Moderators in nuclear reactors

Moderators are provided along with the fissionable nuclei for slowing down fast neutrons. The moderators commonly used are water, heavy water (

D_{2} O

) and graphite. The Apsara reactor at the Bhabha Atomic Research Centre (BARC), Mumbai, uses water as moderator. The other Indian reactors, which are used for power production, use heavy water as moderator.

Definition

Safety measures in establishment of nuclear power plants and safe disposal of nuclear waste

While establishing a nuclear power plant to generate electricity, care must be taken to ensure that the people working in it are not exposed to nuclear radiations and in case of any accident in the nuclear power plant, there is a minimum spread of radiations. Therefore following safety measures must be taken in a nuclear power plant:
1. The nuclear reactor of power plant must be shield with lead and steel walls so as to stop radiations from escaping out to the environment during its normal operations.
2. The nuclear reactor must be housed in an airtight building of strong concrete structure which can withstand earthquakes, fires and explosion.
3. There must be a back-up of cooling system for reactor core, so that in case of failure of the system, the other cooling system could take its place and core is saved from over heating and melting.

Definition

Thermonuclear fusion

To generate useful amount of energy, nuclear fusion must occur in bulk matter. What is needed is to raise the temperature of the material until the particles have enough energy due to their thermal motions alone to penetrate the coulomb barrier. This process is called thermonuclear fusion.Thus, for thermonuclear fusion to take place, extreme conditions of temperature and pressure are required, which are available only in the interiors of stars including sun.

Example

Examples of Nuclear Fusion Reactions

Nuclear fusion is a process when two or more nuclei combine to form a large nuclei and release some energy. These are the examples of Nuclear Fusion Reaction:

1.

_{6} C^{13} +_{1} H^{1} \to_{7} C^{14} + 4.3 M e V

_{6} C^{12} +_{1} H^{1} \to_{7} C^{13} + 2 M e V

_{7} C^{14} +_{1} H^{1} \to_{8} O^{15} + 7.3 M e V

Definition

Energy generation in sun

The fusion reaction in the sun is a multi-step process in which hydrogen is burned into helium, hydrogen being the fuel and helium the ashes. The proton-proton (p, p) cycle by which this occurs is represented by the following sets of reactions:

$_{1}^{1} H +_{1}^{1} H \to_{1}^{2} H + e^{+} + ν + 0.42 M e V$
$e^{+} + e^{-} \to γ + γ + 1.02 M e V$
$_{1}^{1} H +_{1}^{2} H \to_{2}^{3} H e + γ + 5.49 M e V$
$_{2}^{3} H +_{2}^{3} H \to_{2}^{4} H e +_{1}^{1} H +_{1}^{1} H + 12.86 M e V$

For the fourth reaction to occur, the first three reactions must occur
twice, in which case two light helium nuclei unite to form ordinary helium
or nucleus. If we consider the combination 2(1) + 2(3) + 2(3) +(4), the net
effect is