NUCLEAR FISSION
Tuesday, January 26, 2010
<$BlogDateHeaderDate>
Definition:
Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts by the bombardment of slow neutron, often producing free neutrons and lighter nuclei, which may eventually produce photons (in the form of gamma rays).
In 1938, the German chemists Otto Hahn and Fritz Strassmann directed neutrons onto uranium 235 atoms expecting to get transuranium elements. Instead, experiments showed barium as a product. A year later, Lise Meitner and her nephew Otto Frisch verified that Hahn's result were the first experimental nuclear fission. In 1944, Hahn received the Nobel Prize in chemistry.
The reaction equation is:
Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom. Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments. When a uranium nucleus fissions into two daughter nuclei fragments, an energy of ~200 MeV is released. For uranium-235, typically ~169 MeV appears as the kinetic energy of the daughter nuclei, which fly apart at about 3% of the speed of light.
http://www.youtube.com/watch?v=N7C14UlKuv8
Chain reaction:
When an atom undergoes nuclear fission, a few neutrons are ejected from the reaction. These free neutrons will then interact with the surrounding medium, and if more fissile fuel is present, some may be absorbed and cause more fission. Thus, the cycle repeats to give a self-sustaining reaction called chain reaction.
In 1939, Enrico Fermi discovered neutron multiplication in uranium, proving that a chain reaction was indeed possible.
http://www.youtube.com/watch?v=tQa4LONy9XM&NR=1
The smallest amount of fissile material needed for a sustained nuclear chain reaction is called critical mass. The critical mass of a fissionable material depends upon its nuclear properties (e.g. the nuclear fission cross-section), its density, its shape, its enrichment, its purity, its temperature, and its surroundings.
Nuclear Power:
Nuclear power is power (generally electrical) produced from controlled (i.e., non-explosive) nuclear reactions. Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons.
In an atomic bomb, a mass of fissile material greater than the critical mass must be assembled instantaneously and held together for about a millionth of a second to permit the chain reaction to propagate before the bomb explodes.
The principle of atom bomb is uncontrolled chain reaction which releases tremendous amount of energy within a fraction of a second.
http://www.youtube.com/watch?v=hfEMnx-Nz-w&feature=related
Nuclear Reactor:
A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate.
The reactor is used to convert nuclear (also known as 'atomic') energy released from nuclear fission into heat. Thus the most significant use of nuclear reactors is as an energy source for the generation of electrical power.
Breeder reactor:
A breeder reactor is a nuclear reactor that generates new fissile material at a greater rate than it consumes such material.
more fissile material than it consumes. These reactors are used in nuclear power plants to produce nuclear power and nuclear fuel. At present the scientists of the Indira Gandhi Centre for Atomic Research (IGCAR), one of the nuclear R & D institutions of
Essentials of a nuclear reactor:
· Nuclear or "fissile" fuels
Nuclear fuel is any material that can be consumed to derive nuclear energy. The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very tempting source of energy.
The most common nuclear fuels are U- 235, U- 233 and Pu- 239. They are not major radiological hazards by themselves. Of natural uranium, only 0.7% is uranium 235. This meant that a large amount of uranium was needed to obtain the necessary quantities of uranium 235. Also, uranium 235 cannot be separated chemically from uranium 238, since the isotopes are chemically similar.
Scientists knew that the most common isotope, uranium 238, was not suitable for a nuclear fission. There is a fairly high probability that an incident neutron would be captured to form uranium 239 instead of causing fission.
- Reactor core
A nuclear reactor core is that portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.
- Neutron source
Neutron source is a general term referring to a variety of devices that emit neutrons, irrespective of the mechanism used to produce the neutrons. Usual combinations of materials are plutonium-beryllium powder.(Pu-Be).
· Moderator
A neutron moderator is a medium which reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235.
Commonly used moderators include water, solid graphite and heavy water. Beryllium has also been used in some experimental types, and hydrocarbons have been suggested as another possibility.
· Control rod
A control rod is a rod made of chemical elements capable of absorbing many neutrons without fissioning them. They are used in nuclear reactors to control the rate of fission of uranium and plutonium by controlling the amount of free neutrons in the reaction space. Most reactors are controlled by means of control rods that are made of a strongly neutron-absorbent material such as boron or cadmium. Increase or decrease in the rate of fission will also increase or decrease the energy output of the reactor.
- Coolant
A coolant is a fluid which removes heat from the reactor core and transports it to another area of the plant, where the thermal energy can be harnessed to produce electricity or to do other useful work. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor promoting corrosion of the cooling system. Air, Inert gases, water are common form of a coolant.
Working of a Nuclear Reactor:
http://www.youtube.com/watch?v=OOf_tlj_JQU&NR=1
Nuclear Research in 
Homi Jehangir Bhabha (October 30, 1909 – January 24, 1966) was an Indian nuclear physicist who played a major role in the development of the Indian atomic energy program and is considered to be the father of
BARC was started in 1954, as the Atomic Energy Establishment, Trombay (AEET), and became
Some of the important nuclear reactors in
APSARA (1956; named by the then Prime Minister of India, Jawaharlal Nehru), CIRUS (1960; the "Canada-India Reactor" with assistance from Canada), the now-defunct ZERLINA (1961; Zero Energy Reactor for Lattice Investigations and Neutron Assay), Purnima I (1972), Purnima II (1984), Dhruva (1985), Purnima III (1990), and Kamini.
Labels: Nuclear Fission
posted by Lekshmi @ 10:47 PM,
0 Comments:
Post a Comment