Pressurized Water Reactors And The Graphite example essay topic

Nuclear Power Producing energy from a nuclear power plant is very complicated. The process of nuclear energy involves the fission of atoms, the release of energy from fission as heat, and the transfer of heat to electricity in power plants. The process of splitting the atom is called nuclear fission. Fission can take place in many different kinds of atoms. This explanation uses Uranium - 235, the atom most commonly used in nuclear reactors.

The Uranium atom has many protons, thus making it unstable. Since the nucleus of the atom is so unstable it wants to split itself apart, causing a spontaneous fission. When the nuclei of a Uranium atom splits apart, it splits into two atoms. Commonly the nucleus splits into Barium and Krypton; however, it can split into any two atoms as long as the number of protons equals the original amount of the protons found in the Uranium. In addition, a mass amount of energy is released along with two or three neutrons. It is these neutrons that can begin a chain reaction, each neutron that is given off could collide with another Uranium atom splitting it apart.

Each of these fission ing atoms releases a very large amount of energy, and some more neutrons. This process continues causing a chain reaction without any outside assistance, and the Uranium has 'gone critical' (Martindale, 794-195). This chain reaction is the basis for how nuclear power is made. The amount of the energy that is given off in nuclear fission is astronomical. To equal the amount of energy given off when splitting some uranium the size of golf ball, one would have to burn approximately twenty-five train cars full of coal. Presently, the planet contains twenty-five times more nuclear fuel compared to fossil fuel.

On average, an atomic power plant can produce half a million kilowatts of power. As a comparison, a hair dryer takes about one kilowatt (Jenny, 1-2). The producing of energy from nuclear fission is very similar to using a very common fossil fuel boiler. The difference lies in the reactor, where the heat is generated by fission ing material. The most common of reactors is the pressurized water reactor; however, there are many other types. The pressurized water reactor is the most common reactor in the United States.

The reactor of a nuclear power plant is where the fission ing takes place. The Uranium is contained in fuel rods, each rod is sealed so no contamination occurs. Many of these rods are then contained in a fuel assembly. All the fuel assemblies are separated by control rods. The control rods limit the amount of fission taking place by the use of Boron, an element that absorbs neutrons. If the control rod is inserted, it collects the neutrons from the fission ing atoms, which slows down or stops fission taking place in the reactor.

There commonly are 300 to 600 fuel assemblies in one reactor (Michio, 31). Surrounding all of the fuel assemblies is a moderator, water in most cases. The moderator is a substance that is used to slow down the neutrons. The slower the neutrons travel, the more likely they will strike the nucleus of an atom. The process begins when a spontaneous fission takes place and starts the chain reaction. The control rods are the inserted to keep the rate of fission constant, this is called 'going critical'.

As the fission takes place in the fuel assemblies, the kinetic energy (heat) given off is absorbed by the water. The water is under pressure so it will never boil. The water becomes super heated, sometimes above 300 o C, and is then pumped into a heat exchanger. The heat exchanger runs water, at normal pressure, through pipes in the super heated water, boiling the water at normal pressure vigorously. That boiling water quickly turns to steam which is then used to turn massive generators. The generators then turn the kinetic energy into electricity (Weiss, 26).

The steam then is cooled down and returned to the heat exchanger so it will boil again. If there is no need to use the water again, it is pumped into a nearby lake or river. In turn, if more water is needed, it is pumped from a nearby lake or river. If the water in the reactor becomes too hot, it is vented into a cooling tower where the water is condensed to steam and released into the air. Then cool water from a lake or river is pumped into the reactor to cool it down. There are many other ways of utilizing nuclear fission for energy.

Of these, the more popular types are the heavy water reactors, the gas-cooled reactors, the graphite moderated water-cooled reactors, and the fast breeder reactors. The heavy water reactor is mainly found in Canadian reactors, where heavy water is abundant. The heavy water reactor is almost the same as the pressurized water reactor. The pressurized water is heated, and then pumped into a heat exchanger. The pressurized water is used to boil ordinary water, turning it into steam. The steam is then used to turn a generator.

The advantage is that heavy water is used as the moderator. Heavy water is has a special isotope of hydrogen in it. Since heavy water is a larger particle of matter, it slows down the neutrons even more, and less energy wasted. Another benefit of this reactor, is that it doesn't have to be shut down to refuel (Martindale, 797). The gas cooled reactors uses graphite as the moderator and carbon dioxide or helium as the coolant. The gas is heated and then again passed to a heat exchanger where steam is produced to turn the generators.

The gas cooled reactors are most commonly found in Europe (Martindale, 797). Another kind of reactor is the graphite moderated water cooled reactor. This reactor is almost exclusively used in the Soviet Union. This form of reactor isa hybrid of the pressurized water reactors and the graphite moderated reactors. The advantage of using this form of reactor is that it does not have to be shutdown for refueling.

However, because of the poor engineering, this reactor is commonly known for uncontrollable chain reactions leading to meltdowns. This is the type of reactor that melted down in Chernobyl. For this reason no other country is willing to take on the risks connected with this reactor (Foreman, 38). The last type of reactor, the fast breeder reactor, is of a unique design. The core of the reactor still contains uranium - 235; however, lining the walls of the reactor is uranium - 238. When there is little or no moderator to slow the neutrons, some of the stray neutrons strike the uranium - 238 on the walls producing plutonium - 239 or uranium - 233.

Both of these by products are then used as the fuel in the reactor (Martindale, 797). The obvious advantage of this form of reactor is that it takes less of our worlds nuclear fuel to run the plant (Martindale, 797). Nuclear reactors are a complicated form of an energy source. Although similar in the over all form, the nuclear power plants can produce much more energy then the conventional fossil fuel power plants.

SourcesKaku, Michio and Trainer, Jennifer, et al. Nuclear Power: Both sides. Toronto: George J. McLeod Limited, 1982. Foreman, Harry. Nuclear Power and the Public. Minneapolis: University of Minnesota Press, 1970.

Martindale, David, et al. Heath Physics. Lexington: D.C. Heath and company, 1992. Weiss, Ann. The Nuclear Question.

New York: Harcourt Brace Jovanoich, 1981. Jenny and Mike. Atomic Energy. Internet: web.