Nuclear FissionThe greater stability of nuclei with mass number of intermediate values on the periodic table suggest the possibility of spontaneous splitting of less stable nuclei of the heavy elements into fragments of approximately half size and that nuclear fission would be accompanied by the release of large quantities of energy. In 1939 Hahn and Strassman reported that bombardment of a U-235 sample with slow neutrons split the atoms into barium, lanthanum, cerium as well as other elements from the middle of the table, all of which were more stable then the original U-235. This process came to be known as fission. There were to other important by products neutrons and energy.
235U + 10n ==> (Ba, La, Ce, etc.) + 10n + ENERGYIt was found that 0.2 amu per atom were converted to energy. Pound per pound that amounts to 2.5 million times as much energy as coal. A chain reaction can occur where neutrons released from this reaction cause other fusion reactions to take place. If a chain reaction becomes self-sustaining due to its mass, that is the number of neutrons produced by the reaction is equal to, or exceeds, the number of neutrons lost in the reaction, it has reached its critical mass. Critical mass is dependent on the material as well as its shape.
EnrichmentEnrichment is the process of purifying a specific isotope. In nuclear chemistry enrichment of fissionable materials is usually done in order to yield higher products in reactions. One example of enrichment is the fraction distillation of uranium. Uranium is mixed with fluorine to form UF6, a gas. At low pressures the compound is allowed to go through a diffusion barrier permitting the lighter 235U to pass through faster. This is done hundreds of times to finally produce a 3% mixture of 235U.
Breeder ReactorsFission reactors are dependent on the supply of uranium, which is expensive and being depleted at a rate which will be exhausted in approximately 50 years. Although the 238U present in enriched uranium is not fissionable it can still be transmutated into 239Pu, a fissionable material. Some, but not all 238U reacts as follows:
238U + 1n ==> 239Pu + 2 0eThe plutonium produced then put through the fission reaction
239Pu + 1n ==> 147Ba + 90Sr + 3 1nThe neutrons produced are then used to make more 239Pu from 238U. Reactors that are specially designed to harvest the Pu are breeder reactors. By definition a breeder reactor is any reactor that creates more fissionable matter then it started out with. This sounds great but plutonium is the most toxic material known to man. It is widely held that one atom of plutonium can kill you if it gets into your lungs.
Nuclear FusionThe process of converting light nuclei into heavy nuclei is accompanied by an even larger amount of energy. This type of reaction is known as nuclear fusion. When deuterium (hydrogen 2--with one neutron) and tritium (hydrogen 3--with two neutrons) are exposed to very high temperatures helium and neutrons are produced.
2H + 3H ==> 4He + 1n + ENERGYIn this reaction MUCH more energy is released. For this reason, there are numerous research projects going on in order to find a way to control this reaction within so its energy can be harvested. Should this energy source be tapped, the worlds oceans would be an inexhaustible supply of cheap, clean, energy.
Fusion ReactorsHarvesting the energy released by a fusion reaction has attracted the attention of many research operations. Fusion is cheap and clean taking deuterium from ordinary water and producing stable, non-radioactive isotopes. The major draw back to this is the required energy to overcome the charges on the positive hydrogen nuclei. Temperatures of about 108 K are required to overcome the positive charge on the reacting nuclei. NOTHING known to man can withstand such temperature for any extended period of time. Even if we knew of such materials, the nuclei would a have lot of energy when colliding with the container walls. Magnetic confinement and laser implosion methods are ways of implementing fusion power.
Inerital confinement, or laser implosion means inclosing the fuel, tritium and deuterium, with a pellet and having high energy lasers shoot at it with the same force from all sides. This causes the pellet to implode into a dense, hot ball of plasma, where fusion could occur.
Magnetic confinement holds the plasma to prevent it from leaking out, since no known material can withstand the temperatures. This is done by shaping and holding magnetic forces in configurations that prevent the plasma from moving out.