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Sub Critical Nuclear Test Explosion: It is a type of test in which an experiment does not reach a point of criticality or a self sustaining chain reaction. Such a test does not released nuclear energy and is also known as zero yield nuclear test explosion. This test is conducted to check the stability and reliability of nuclear stockpiles i.e. existing nuclear weapons. In this test physical property of Pu under condition relevant to performance of nuclear weapons are understood. This helps in resolving age related problems of the nuclear components. This type of test is prohibited under CTBT.

Laboratory Test Explosion: It is a computer simulated nuclear test explosion created on a computer screen. It is a sort of substitute to the physical test explosion of nuclear weapons. This facility enables a country to constantly upgrade its Nuclear Arsenal by redesigning its nuclear weapons. The aim of this test to produce a computer base virtual weapon design and production ready prototype capability. This type of test does not prohibited under CTBT. The USA possess this capability having carried out more than 1100 test explosion thus a large data base to developed a soft- ware programme and with the development of its own super computer. It is claimed that India also possesses this capability with the development of Param Padma and Param 10,000 processing Super computers.

Low field Nuclear Weapon / bomb: It is a nuclear weapon that has an explosive yield in single digit kilotones. It is used as a tactical nuclear weapon (Tactical- operates over a shorter area for short time, Strategic – operates over a larger area for longer time). India carried out test of this nature in 1998.

Fusion Bomb or Thermonuclear Bomb or Hydrogen Bomb: It uses isotopes Hydrogen called Deuterium and Tritium as fuel and needs a fission bomb to act as a trigger. Its explosive yields in the range of 60 millions of kilotonnes. India exploded a device of its nature in 1998. More heat is produced.

Neutron Bomb: It is nuclear bomb that produces large amount of radiations and relatively a small blast. It is also called as enhanced radiation weapon. It is essentially a low yield thermonuclear device where the neutron producing process- fusion process dominates over the other process. It releases massive waves of neutrons and radiations which destroy life and leave properties intact. No country at present possesses a neutron bomb.

Nuclear Winter: The continuous sub zero winter conditions for months together caused due to a nuclear holocaust that throws dust, smoke and soot into the atmosphere which blocks the sun light from reaching the surface of the earth is known as Nuclear winter.

Nuclear Fusion: A nuclear fusion is a nuclear reaction between light atomic nuclei as a result of which a heavier nucleus is formed and enormous quantity of nuclear energy is released. For Fusion to be possible the reacting nuclei must possess sufficient kinetic energy to overcome the repulsive force between the nuclei. Temperature associated with fusion reaction is extremely high in the range of millions of degree centigrade

The fusion reaction is almost free from radioactive follow and there is no associated problem of disposal radioactive spent fuel. The fusion reaction produces Helium nuclei and nuclear energy thus it does not pollute the environment and it is a clean source of energy if harnessed for constructive use. Further the fuel needed for fusion process is available in plenty in the form of Hydrogen in H20. It is a near inexhaustible source of energy. Further, more a fusion reactor by its very nature can not explode and at worse it will collapse and reaction would come to an end.

Nuclear Fusion Reactor: This reactor is built on the basis of TOKAMAK technology which is a Russian acronym stands for Toroid Kamera (chamber) Magnit Katuska (oil) which means “Toroid Magnetic Chamber”. It is a “doughnut-shaped chamber enclosed by powerful superconducting magnets which by repulsive force keep atomic nuclei that are in the state of plasma and thus electrically conducting within the chamber without physically contact with the plasma. This helps in not only contain the plasma within the chamber but also in maintaining the high temperature which is essential for igniting and sustaining the fusion reaction.

Fusion Research in India: Fusion research has been going on at BARC, TROMBAY, Tata Institute of Fundamental Research Mumbai, Saha institute of Physical Research at Kolkata and Physical Research Laboratory (PRL) at Ahmedabad. Research at PRL led to the establishment of I.P.R. at Gandhi Nagar in 1986. The I.PR has succeeded in designing and fabricating and commissioning India’s first TOKOMAK called ADITYA in 1989. It can generate Plasma of temperature up to 5 million degree centigrade. The basic objective of ADITYA is to provide fundamental information on plasma stability and confinement. In 1995 India took the decision to built the second Generation TOKOMAK called Super Steady TOKOMAK I (SST I). It’s objective is to increase the plasma confining time. The SST passed the basic principle of ITER designed as well which enabled I India to get admission into the ITER Project in December 2005.


  •    Nuclear Reaction: The spontaneous distintegration of nuclei of some of the heavier elements and the release of nuclear energy is called Nuclear Reaction.

Natural (isotopes) uranium    –   238U92 (92 Proton +                                                           146 Neutron); U -238

Enriched uranium                    –   235U92 (92Proton +                                                            143 Neutron); U-235

Thorium derived uranium      –   233U92 ( 92proton +                                                           141 Neutron); U-233

  •    Fission Reaction: In a fission reaction some of the nuclei of heavier elements like Uranium and Plutonium spontaneously spit into smaller nuclei and in this process release nuclear energy.
  •   Nuclear Chain Reaction: When a nucleus is bombarded with the help of instrument like cyclotron the nuclei of elements like Uranium and Plutonium undergo nuclear reaction and release nuclear energy and two or more nucleus. These nucleuses in turn bring about nuclear reaction in other nuclei thus a nuclear reaction is capable of self sustaining which is known as Nuclear Chain Reaction. When nuclear reactor achieve nuclear chain reaction it is said to have become critical. In order to keep the nuclear chain reaction and at steady rate control Rods like Boron and Cadmium are used to keep the reaction under continuous and check.
  •    Nuclear Fuel : Nuclear fuels are of tow types-
  1. Fissile material
  2. Fissionable material
  3. Fissile Material: It is one which readily under goes nuclear fission and thus can be used as nuclear fuel in a nuclear reactor. Eg. Plutonium. Natural Uranium, Enriched Uranium and Thorium derived Uranium.

      Plutonium: It has atomic number of 94. It is a transuranic element. Transuranic elements are not occurring in nature. They are man made in nuclear reactor. Plutonium is consider to be as the ideal nuclear fuel because of following reason-

  1. It releases more nuclear energy per unit mass than any.
  2. It under goes nuclear reaction when bombarded by fast moving or slow moving neutrons.
  3. It releases less xenon gas which is radioactive and dangerous.
  4. Plutonium has a higher breeding ratio than any other nuclear fuel.

Plutonium occur in to different isotopes namely ^gPu94 and ^Pu94

  •    239Pu94: It is called weapon’s grade plutonium. It under goes nuclear fission more steadily and thus does not crumble too early. Thus Pu-239 builds up a power blast. Further the yield of nuclear energy is more predictable. The concentration of Pu-239 must be over 90% in order that it can be use as a fuel in manufacturing nuclear weapons. The critical man of Pu-239 if used as a fuel in a nuclear weapon is 4 kg. India’s nuclear weapons program is based on Pu-239.
  •    240Pu94: It s called reactor grade plutonium. Pu-240 under goes fission rapidly and thus it crumble too early and can not build up a powerful blast. Moreover, the yield of nuclear energy is not quite predictable. It is primarily used as a nuclear fuel in a nuclear reactor for power generation. India has succeeded in establishing a reprocessing technique for separating Pu-239 and Pu-240 isotopes.
  •    93U239 (Natural Uranium): It is poor nuclear fuel. It under goes nuclear fission when bombarded by fast moving neutron. When it is used as a fuel the nuclear reactor does not need a moderator like heavy H20 to slow down the speed of neutron.
  •    93U235 (Enriched Uranium): The natural uranium is that is mined contains upto 0.7% U-235. The separation of U-235 isotopes from U-238 is called enrichment of uranium. It is done with the help of ring magnets or nuclear lasers. The nuclear laser provides the fastest and the most economic method of enriching uranium. The BHABA Atomic Research Centre (BARC) developed a nuclear laser for enriching Uranium.
  •    U-235 is the second best nuclear fuel after Plutonium. It under goes nuclear fission when bombarded by a slow moving neutron. A slow moving neutron is called thermal neutron. The reactor that makes use of U-235 as a fuel makes use of a moderator preferably heavy H20 to slow down the speed of neutrons.
  •    Low Enriched Uranium – If the concentration of U- 235 isotopes is 3% to 4% then it is called low enriched uranium. It is used as a fuel in a nuclear reactor.
  •    High Enriched Uranium- If the concentration of U- 235 isotopes are more than 4% then it is called the high enriched uranium.
  •    Highly Enriched Uranium- If the concentration of U-235 isotopes is more than 90% then it is called the highly enriched uranium. It is used in manufacturing of nuclear weapons. Pakistan nuclear program is based on highly enriched uranium. The critical mass of nuclear fuel (U235) in a bomb is 10kg.
  •    Thorium Derived Uranium U-233- It does not occur in nature but is produced in a nuclear reactor by the process of neutrons irradiation where thorium under goes transmutation into U-233. (Transmutation – conversion from one element into another). Uranium-233 is a good nuclear fuel better than U-238.
  •    2-Fissionable Material: It is one which does not readily under goes nuclear fission but is capable of conversion into a fissile material in a nuclear reactor by the process of neutrons irradiation. Eg. Thorium, U-238.

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