NUCLEAR REACTOR444444



An assembly in which a nuclear fission chain reaction is maintained and controlled for the production of nuclear energy, radioactive isotopes, or artificial elements. The nuclear fuel used in a reactor consists of fissile material (e.g. uranium-235 which undergoes fission as a consequence of which two nuclides of approximately equal mass are produced together with between two or three neutrons and a considerable quantity of energy. These neutrons cause further fissions so that a chain reaction develops. In order that the reaction should not get out of control, its progress is regulated by neutron absorbers in control rods, only sufficient free neutrons being allowed to exits in the reactor to maintain the reaction at a constant level. The fissile material is usually mixed with a moderator which slows down, or thermalizes, the fast neutrons emitted during fission, so that they are more likely to cause further fissions of the fissile material than they are to be captured by the uranium-238 isotope.

In a heterogeneous reactor the fuel and the moderator are separated in a geometric pattern called a lattice. In a homogeneous reactor the fuel and the moderator are mixed so that they present a uniform medium to the neutrons (e.g., the fuel, in the form of a uranium salt, may be dissolved in the moderator).

Besides this classification, reactors may be described in a number of ways. They may be described in terms of neutron energy (see fast reactor and thermal reactor) or in terms of function, e.g., a power reactor for generating useful electric power, a production reactor for manufacturing fissile material (see also breeder reactor and converter reactor) and a propulsion reactor for supplying motive power to ships, submarines, or spacecraft. Reactors are also described in terms of their fuel (e.g., plutonium reactor), their moderator (e.g. graphite-moderated reactor), or their coolant (e.g., boiling-water reactor).

CHAIN REACTION

CHAIN REACTION

When a uranium nucleus undergoes fission, three neutrons are produced. These neutrons collide with other uranium nuclei producing nine secondary neutrons. Thus the process gets multiplied quickly. This is called the chain reaction. If it is not controlled the chain reaction continues till the entire fissionable material is disintegrated in a short time emitting a large quantity of heat energy. This causes a violent explosion resulting in the release of tremendous energy in the form of heat and light. This is the basic principle of an atom bomb.


PLS ADD THE VEDIO CLIPS OF CHAIN REACTION

CONSEQUENCES OF NUCLEAR FISSION-AFTER EFFECT OF ATOM BOMB(HIROSHIMA AND NAGASAKHI)

PLS DO ADD THE NUCLEAR FISSION VEDIO -PHYSICSNUCLEAR FISSION e=MC2

NUCLEAR FISSION

NUCLEAR FISSION
The breaking of a heavy nucleus into two or more fragments of comparable masses, with the release of tremendous energy is called as nuclear fission. The most typical fission reaction occurs when slow moving neutrons strike 92U235. The following nuclear reaction takes place.
If more than one of the neutrons produced in the above fission reaction are capable of inducing a fission reaction (provided U235 is available), then the number of fissions taking place at successive stages goes increasing at a very brisk rate and this generates a series of fissions. This is known as chain reaction. The chain reaction takes place only if the size of the fissionable material (U235) is greater than a certain size called the critical size.
92U235 + 0n1 ——> 56Ba141 + 36Kr92 + 3 0n1 + 200 MeV
If the number of fission in a given interval of time goes on increasing continuously, then a condition of explosion is created. In such cases, the chain reaction is known as uncontrolled chain reaction. This forms the basis of atomic bomb.
In a chain reaction, the fast moving neutrons are absorbed by certain substances known as moderators (like heavy water), then the number of fissions can be controlled and the chain reaction is such cases is known as controlled chain reaction. This forms the basis of a nuclear reactor.

QUESTION

1.WRITE THE USES OF RADIOACTIVE DECAY.
2.WHAT IS THE SI UNIT AND OLD UNIT OF RADIOACTIVITY.
3.BETA PARTICLES COME FROM THE NUCLEUS AND THEY ARE ELECTRONS, BUT THERE NO ELECTRONS INSIDE THE NUCLEUS. EXPLAIN THIS PARADOX.

APPLICATION OF RADIOACTIVE DECAY

Applications of radioactivity

In medicineRadioisotopes have found extensive use in diagnosis and therapy, and this has given rise to a rapidly growing field called nuclear medicine. These radioactive isotopes have proven particularly effective as tracers in certain diagnostic procedures. As radioisotopes are identical chemically with stable isotopes of the same element, they can take the place of the latter in physiological processes. Moreover, because of their radioactivity, they can be readily traced even in minute quantities with such detection devices as gamma-ray spectrometers and proportional counters. Though many radioisotopes are used as tracers, iodine-131, phosphorus-32, and technetium-99m are among the most important. Physicians employ iodine-131 to determine cardiac output, plasma volume, and fat metabolism and particularly to measure the activity of the thyroid gland where this isotope accumulates. Phosphorus-32 is useful in the identification of malignant tumours because cancerous cells tend to accumulate phosphates more than normal cells do. Technetium-99m, used with radiographic scanning devices, is valuable for studying the anatomic structure of organs.

Such radioisotopes as cobalt-60 and cesium-137 are widely used to treat cancer. They can be administered selectively to malignant tumours and so minimize damage to adjacent healthy tissue.

In industryForemost among industrial applications is power generation based on the release of the fission energy of uranium (see nuclear fission; nuclear reactor: Nuclear fission reactors). Other applications include the use of radioisotopes to measure (and control) the thickness or density of metal and plastic sheets, to stimulate the cross-linking of polymers, to induce mutations in plants in order to develop hardier species, and to preserve certain kinds of foods by killing microorganisms that cause spoilage. In tracer applications radioactive isotopes are employed, for example, to measure the effectiveness of motor oils on the wearability of alloys for piston rings and cylinder walls in automobile engines. For additional information about industrial uses, see radiation: Applications in science and industry.

In scienceResearch in the Earth sciences has benefited greatly from the use of radiometric-dating techniques, which are based on the principle that a particular radioisotope (radioactive parent) in geologic material decays at a constant known rate to daughter isotopes. Using such techniques, investigators have been able to determine the ages of various rocks and rock formations and thereby quantify the geologic time scale (see geochronology: Absolute dating). A special application of this type of radioactivity age method, carbon-14 dating, has proved especially useful to physical anthropologists and archaeologists. It has helped them to better determine the chronological sequence of past events by enabling them to date more accurately fossils and artifacts from 500 to 50,000 years old.

Radioisotopic tracers are employed in environmental studies, as, for instance, those of water pollution in rivers and lakes and of air pollution by smokestack effluents. They also have been used to measure deep-water currents in oceans and snow-water content in watersheds. Researchers in the biological sciences, too, have made use of radioactive tracers to study complex processes. For example, thousands of plant metabolic studies have been conducted on amino acids and compounds of sulfur, phosphorus, and nitrogen.