NUCLEAR FUSION
Tuesday, January 26, 2010
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Nuclear fusion is the process by which multiple atomic nuclei join together through the energetic collision to form a heavier nucleus.
Fusion is like lighting a match to a bucket of gasoline. You need that input energy (the match), but what you get as a result is far more powerful. Thus higher temperatures are needed to cause the nuclei to collide and fuse. Such a condition where the thermal energy (how hot it is) of nuclei is high enough to fuse despite their repulsion is called thermonuclear. 
In Nuclear Fusion the nuclei of atoms fuse together, causing much more energy being released than in Nuclear Fission. This is the process which powers the Sun. The nuclei used by the sun, and in experiments on earth, that undergo fusion, are two isotopes of hydrogen called deuterium and tritium.
Nuclear fusion occurs naturally in stars. Here the Deuterium 
and Tritium atoms (these are the isotopes of Hydrogen) fuse together to form He. The reaction yields 17.6 MeV of energy due to a very large mass deficit (m) between He atoms compared with the sum of the Hydrogen atoms but requires a temperature of approximately 40 million Kelvins to overcome the coulomb barrier and ignite it. Thus at the core of the Sun, protons require energies of 3–10 keV to overcome their mutual repulsion—the coulomb barrier—and fuse together into a single nucleus.
http://www.youtube.com/watch?v=l9HXAXXyU0U&NR=1
http://www.youtube.com/watch?v=fSr3V498A3l&feature=related
Fusion has been used here on earth to produce nuclear bombs. In order to cause nuclei to fuse here on earth (and release their stored energy), they must either be heated to that temperature, or caused to move fast enough to simulate a correspondingly high temperature. The energy to set off the fusion reaction was supplied by an atomic bomb, and the fusion reaction that resulted was called a 'hydrogen bomb'! But the energy release was all at once, and uncontrollable. When the fusion reaction is a sustained uncontrolled chain reaction, it results in a thermonuclear explosion, such as that generated by a hydrogen bomb.
http://www.youtube.com/watch?v=A8rXc21d2ms&feature=related
While scientists were easily able to control atomic explosions, to create reasonably safe nuclear energy in atomic power plants, no such controlled reaction has yet been achieved for fusion. Nuclear fusion indeed looks like it may be the power source of the future!
Pros and Cons of Nuclear Fusion:
|
PROS |
CONS |
| There is a lot more energy released during fusion than fission so would be more profitable once set up. | Fusion will only occur at temperatures of 10-15 million Kelvin (K), hence there is no point of producing energy since it is not profitable. |
| Hardly any waste produced compared to Nuclear Fission, so no money wasted in disposing Nuclear waste. | Even if fusion did take place, it would be far ahead of it’s time since no material exists which can cope with temperatures of 10-15 million K. |
| Fusion could power the entire world at a very low cost compared with power sources today. Fusion would not be depleted like non-renewable sources today since it would be possible to make hydrogen nuclei manually as it is a very simple element (requires only 1 proton and 1 neutron). | At the moment the only profitable way for fusion to occur is using cold fusion*, but this has not yet been discovered. (*cold fusion is fusion at low enough temperatures to make profits because this would mean that the output energy would be greater than input energy). |
Advantages of Fusion:
- Abundant Fuel Supply
The major fuel, deuterium, may be readily extracted from ordinary water, which is available to all nations. The surface waters of the earth contain more than 10 million tons of deuterium, an essentially inexhaustible supply. The tritium required would be produced from lithium, which is available from land deposits or from sea water which contains thousands of years' supply.
- No Risk of a Nuclear Accident
The amounts of deuterium and tritium in the fusion reaction zone will be so small that a large uncontrolled release of energy would be impossible. In the event of a malfunction, the plasma would strike the walls of its containment vessel and cool.
- No Air Pollution
Since no fossil fuels are used, there will be no release of chemical combustion products because they will not be produced.
- No High-level Nuclear Waste
There will be no fusion products formed to present a handling and disposal problem. Radioactivity will be produced by neutrons interacting with the reactor structure, but careful materials selection is expected to minimize the handling and ultimate disposal of activated materials.
- No Generation of Weapons Material
Another significant advantage is that the materials and by-products of fusion are not suitable for use in the production of nuclear weapons.
- Help economic growth as a reliable electricity supply
Thus the abundance of raw materials, their wide distribution, and the environmental acceptability of fusion are augmented by the expectation that fusion energy will be an economical source of electricity generation.
Difference between Fission and Fusion:
| FISSION | FUSION |
| Breaking up of a heavy nucleus into two light nuclei. | Two nuclei combine to form a heavy nucleus. |
| The energy released per unit mass is less. | The energy released per unit mass is greater than that of fission. |
| Requires only a low temperature to initiate fission. | Requires extremely high temperature to initiate fusion. |
| It is a spontaneous process. | It occurs usually in steps. |
Radiation Hazards:
There is always the risk of a nuclear power plant accident, like what took place in
Radiation outside the Body
Beta particles and gamma rays are the most dangerous outside the human body. They can both penetrate the skin and damage the cells in organs such as the liver or lungs. Alpha particles are not as dangerous. They cannot penetrate the skin and cause damage.
Radiation inside the Body
Radiation from alpha particle sources is the most dangerous inside the human body. Alpha particles can ionise the molecules in many cells and this ionisation can damage or even destroy the molecules and hence the cells.
Beta particles and gamma rays are not as dangerous. They tend to pass through the body without ionising molecules and damaging living cells.
Some radiation hazards are:
Nuclear Power Plants release radioactive rays to the surroundings. Nuclear waste disposal is still a problem and nuclear weapons test shake the balance of the continents. This is a serious threat to the Bio-diversity.
· Any exposure to ionizing radiation increases one's chances of developing cancer, the worst hazard of radiation exposure. Exposure to radiations causes childhood leukemia, adult leukemia, neurodegenerative diseases (such as amyotrophic lateral sclerosis), miscarriage, and clinical depression.
The picture below shows a small amount of radiation entering a living cell.
The low dose of radiation results in minor damage but not the death of the cell. The cell may divide; however, leading to cancer cells being formed.
http://www.youtube.com/watch?v=LHPFz1UnP3o&feature=related
The picture below shows a growth that has formed due to multiplying cancer cells. This person worked with X-ray machines - sources of high dose radiation.
http://www.youtube.com/watch?v=A1Fkdt-2veM&feature=related
· Intermittent (but not continuous) exposure of human
cells to radiation cause significant increase of DNA fragmentation. It results in genetic mutation.
http://www.youtube.com/watch?v=vNWwSL55gUM&NR=1
· Exposure to radiations causes birth defects.
· Exposure to radiations causes Cell Reproductive Death [most common] - The cell containing the defective DNA may be unable to reproduce itself, so that although it may be able to function normally for its remaining natural lifetime, when it dies a natural death it will not have a new cell to replace it.
Radiation Symbols:
· Radiation Sign
The international radiation symbol (also known as trefoil) first appeared in 1946, at the
The modern version is black against a yellow background, and it is drawn 
with a central circle of radius R, an internal radius of 1.5 R and an external radius of 5 R for the blades, which are separated from each other by 60°.
· Food Irradiation Symbol (Radura logo)
The Radura is the international symbol indicating a food 
product has been irradiated. Food irradiation is the process of exposing food to ionizing radiation to destroy microorganisms, bacteria, viruses, or insects that might be present in the food. The Radura is usually green and resembles a plant in circle. The top half of the circle is dashed. Graphical details and colours vary between countries.
Labels: Nuclear Fusion
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