- A nuclear reactor uses U²³⁵ or Pu²³⁹ as fuel, where controlled nuclear fission produces large amounts of energy.
- A moderator (heavy water, graphite, or beryllium oxide) slows down fast neutrons to thermal energies, sustaining the chain reaction.
- Control rods made of cadmium or boron absorb excess neutrons and regulate the rate of fission.
- A coolant removes heat produced by fission and transfers it to water, generating steam for electricity production.
- Reactors are used for power generation, production of Pu²³⁹, neutron beams, and artificial radioisotopes, and are protected by shielding and safety devices.
Definitions [10]
Definition: Nuclear Reactor
A nuclear reactor is a device in which a self-sustaining controlled chain reaction is produced in a fissionable material.
OR
Nuclear reactor is a device which works on the principle of nuclear fission by sustained chain reaction, to release nuclear energy at a constant rate.
Definition: Stellar Energy
Stellar energy is the energy obtained continuously from the sun and the stars.
Definition: Nuclear Chain Reaction
A nuclear chain reaction is a process in which neutrons produced in one fission reaction cause further fissions, leading to a self sustaining series of nuclear reactions.
Definition: Nuclear Fusion
When two or more very light nuclei moving at very high speeds are fused together to form a single nucleus, then the process is known as ‘nuclear fusion’.
OR
When two or more light nuclei combine to form a heavier stable nuclide, part of the mass disappears and is converted into energy. This phenomenon is called nuclear fusion.
Definition: Nuclear Fission
Nuclear fission is a process in which a heavy nucleus, after capturing a thermal neutron (having energy 0.027 eV), splits up into two lighter nuclei of comparable masses.
OR
Nuclear fission is a disinteg.ration process, in which a heavier nucleus gets split up into two lighter nuclei, with the release of a large amount of energy.
Definition: Multiplication or Reproduction Factor
A chain reaction once started in a fissionable material, will remain steady, decreases or increases, depends on a parameter known as multiplication or reproduction factor (K).
Definition: Uncontrolled Chain Reaction
An uncontrolled chain reaction is a chain reaction in which more than one neutron from each fission causes further fissions, leading to a rapid increase in reactions and a violent release of energy (as in a nuclear bomb).
Definition: Controlled Chain Reaction
A controlled chain reaction is a chain reaction in which, on average, only one neutron from each fission causes further fission, so the reaction proceeds at a steady rate (as in a nuclear reactor).
Definition: Thermonuclear Energy
Since very high temperatures are needed for the fusion of nuclei, the process is called a 'thermonuclear reaction', and the energy released is called as 'thermonuclear energy'.
Definition: Nuclear Holocaust
“Nuclear holocaust means large-scale destruction and devastation that would result by the use of nuclear weapons.”
Formulae [1]
Formula: Multiplication or Reproduction Factor
K = \[\frac{\text{Number of neutrons present at the begining of present generation}}{\text{Number of neutrons in the begining of previous generation}}\]
Key Points
Key Points: Nuclear Fission
- U²³⁵ undergoes fission by slow neutrons, forming an unstable U²³⁶ nucleus which splits into two lighter nuclei, releasing 2–3 neutrons and large energy (~200 MeV).
- The energy released per fission is about 200 MeV, due to the increase in binding energy per nucleon of the fission fragments.
- Fission of 1 g of U²³⁵ releases about 8.2 × 10¹⁰ J, which is equivalent to the explosion of about 20 tons of TNT.
Key Points: Difficulties in the Maintenance of Chain Reaction
- Fast neutrons produced in fission are mostly absorbed by U²³⁸, so moderators like graphite or heavy water are used to slow them down and help continue the reaction.
- The uranium must have a minimum size (critical mass); otherwise, neutrons escape and the chain reaction stops.
Key Points: Parts of Nuclear Reactor
Key Points: Nuclear Fusion
- In nuclear fusion, light nuclei combine to form a heavier nucleus, and a small mass deficit releases large amounts of energy.
- Fusion of deuterium releases about 21.6 MeV, and energy per unit mass is greater than in fission.
- Very high temperature (about 10⁸ K) and high pressure are required to overcome repulsion between nuclei.
- Controlled fusion is difficult because the hot plasma cannot be easily contained, so magnetic fields are used to try to confine it.
