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Nuclear energy is generated when an atom of a fissile material splits into 2 (nuclear fission) or when two or more atomic nuclei collide at a very high speed and join together to form a new type of atomic nucleus (nuclear fusion).
An example of nuclear fission is when Uranium 235 splits into Krypton and Barium (the figure to the right illustrating fissile split is obtained from Wikipedia) .
An example of nuclear fusion is when deuterium and tritium (two isotopes of hydrogen) fuse together to form a nucleus of helium and a neutron (the figure to the left below illustrating fusion is from Wikipedia / Atomic Archive).
Each of the two reactions generate tremendous heat which can be annexed for use in nuclear power plants to provide energy.
In the way they generate energy, nuclear plants are similar to coal and hydroelectric plants; the fuel type (coal, water or fission / fusion materials) differentiate one plant from the other. The applicable fuel, in each case, creates motion that drives the plant. Coal and fissile materials generate heat that creates the steam used to power the coal plant turbine and nuclear plant turbine respectively, while the power of moving water fires the turbine of an hydroelectric plant.
Nuclear fission is the most widely used in nuclear reactors, as nuclear fusion is still in the experimental stage, and uranium is the commonly used fissile material. However, nuclear fusion is believed to be safer than nuclear fission and it's probably one of the hopes of the world's future energy supply.
Uranium occurs naturally in several parts of the World and it is mined from the ground just like other mineral resources. Uranium is mined, cleaned and then processed into small pellets. A small pellet emits very little radiation, but has the potential to produce tremendous energy when involved in atomic splitting (or fission). The uranium pellets are sealed into metal tubes and welded together to form fuel bundles. The fuel bundles are inserted into a large tank and that constitutes the core of the nuclear reactor. The other two (2) main parts of a nuclear reactor are the steam generating unit and the cooling unit. (ref: the line diagram below).
In the core of the nuclear reactor, a uranium atom splits into two (2) when hit by a neutron. This reaction generates heat and releases at least two or more free neutrons that proceed to hit other nuclei thereby producing a series of chain reactions that continue for as long as the nuclei is still big enough to split into two. The core is usually surrounded by a moderator. The moderator ensure sustained fission in the core of the reactor. The commonly used moderators are water, heavy water and graphite. Heavy water is 10% heavier than ordinary water because it contains higher than normal proportion of deuterium, (an isotope of hydrogen).
The type of moderator used in a reactor can be used to classify the reactor. Hence common reator types are classified as follows:
- Boiling Water Reactor (BWR);
- Pressurized Water Reactor (PWR);
- Pressurized Heavy Water Reactor (PHWR);
- Graphite Gas Reactor (GGR).
PWR and PHWR are, these days, the most frequently used. They both have similar configuration as illustrated in the figure below.
A line diagram for a nuclear reactor, particularly PWR and PHWR (Source: Clean Energy Fuels)
A large number of reactors in France and other parts of Europe are based on PWR, while PHWR is commonly used in North America (particularly in Canada).
The moderator surrounding the fuel bundles in the core, slows down the neutrons, so that they are more likely to hit and split the uranium atom and ensure a chain reaction of atom splitting and a constant source of heat, to heat the moderator. The heated moderator is pumped through the reactor to a set of boilers where it boils ordinary water to high pressure steam. The moderator is then re-circulated back to the reactor, while the high pressure steam produced is transported through pipes and directed to power a large turbine connected to an electromagnetic system that generates the required power (electricity) to run operations. The steam is then condensed back into water using cooling water from a large body of water (man-made or preferably natural water body). Due to the considerable amount of water required for cooling, it is not uncommon to see nuclear plants located close to a large body of natural occuring water. For more details, please refer to the diagram above.
Modern nuclear powered plants use the same type of turbines and generators as the coal fired and hydroelectric powered plants. Nuclear plants cost about the same as coal plants but nuclear plants could be more expensive to install.
Advantages of Nuclear Power Plants
- Nuclear power plants do not produce smoke or carbon dioxide and so they do not contribute to the greenhouse effect;
- They produce huge amounts of energy from small amounts of fuel (uranium), compared to other power plants;
- They also produce small amounts of waste;
- Nuclear power plant energy supply is very reliable.
Disadvantages of Nuclear Power Plants
- Nuclear energy produced by using uranium is non-renewable. Uranium has got the potential to be depleted through continuous mining without immediate replacement
- Nuclear reactors are very expensive. Installing 1 reactor costs billions of dollars;
- Nuclear reactors need to be operated with care; little mistakes can cause catastrophic damages (e.g. Chernobyl Nuclear Resident Accident, in Ukraine,1986 and the Three Mile Island or Three Mile Island Accident nuclear accident in Daughin County, PennSylvania, 1979;
- There are currently no good technology for safely managing nuclear wastes; most proposed methods are very expensive and still require proofs of reliability. Many nuclear plant operators still dump ("dispose") their wastes in large water bodies; and
- Nuclear wastes (e.g. spent fuels) or even unused uranium rods/pellets can fall into the hands of those that will use them for destructive purposes. Nuclear energy is sometimes discouraged to minimize or prevent the proliferation of nuclear weapons.
Other Similar or Related Sites.
- Ontario Power Generation
- International Atomic Energy Agency
- International Nuclear and Radiological Event Scale. Other links: INES HTML - (IAEA Website) or INES pdf - (IAEA Website)
- Chernobyl Disaster
- Findings show promise for nuclear fusion test reactors
- Control The Nuclear Power Plant (Demonstration)
- The Virtual Nuclear Tourist: Nuclear Power Plants Around the World
- Howstuffworks - "How Nuclear power Works"
- U.S. Nuclear Regulatory Commission (USNRC)
- FEMA's Nuclear Power Plant Emergency Fact Sheet