Nuclear Energy

- Nuclear Power plants are similar to Coal powered plants and hydroelectric powered plants in the way they produce electricity. The difference in the systems is their fuel sources. Essentially, the three technologies produce the energy that drives the turbine and the electromagnetic rotor which creates flow of electrons (or electricity). In coal powered plants, coal is burnt and the heat is used to generate stem which is used to drive the turbine and the electromagnetic rotor. In hydroelectric power plants, the power of the moving water drives the turbine. Nuclear power plants use the heat generated from the atomic fission of Uranium or any other fissile (materials capable of undergoing fission) to produce the steam that is used to turn the turbine.

 Uranium occurs naturally in several parts of the World and it is mined from the ground just like other metals. Uranium is processed into small pellets. A small pallet emitsUranium Pellets very little radiation, but has the potential to produce tremendous energy when involved in atomic splitting (or fission). Uranium pellets are sealed into metal tubes and welded together to form fuel bundles. The fuel bundles are inserted into a large tank which is the core of the nuclear reactor.

In a nuclear reactor, a uranium atom splits into 2, in a process called fission, when hit by a neutron and this results in a tremendous amount of heat.

Each fission reaction releases at least two or more free neutrons that proceed to hit other nuclei to produce more reactions. This leads to a series of chain reactions that continues for as long as the nuclei is still big enough to split into two. The energy released in the process is used to produce steam used to drive steam turbine that generates electricity. Nuclear fusion (two nuclei binding together) is another reaction that generates energy, but all currently existing commercial nuclear power plants adopt the nuclear fission approach; nuclear fusion is still in experimental stage.

A nuclear reactor consists of three (3) man parts: (i) the nuclear core, described above; (ii) the steam generating unit and (iii) the cooling unit. The core is usually surrounded by a moderator. There are different kinds of lines of nuclear reactors differentiated by their moderator or the thermal fluid carrier that generates the steam. Commonly used moderators are water, heavy water and graphite. Hence there are:


  • Boiling Water Reactor (BWR);

  • Pressurized Water Reactor (PWR);

  • Pressurized Heavy Water Reactor (PHWR);

  • Graphite Gas Reactor (GGR) and so on.

PWR and PHWR are the most commonly used these days. There principles are the same as illustrated in the figure below.

Nuclear Energy Line Diagram

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 description below is based on Heavy Water as a moderator in a pressurized vessel, but the discussion is also valid for ordinary water as a moderator and indeed for other types of moderators.

Heavy water is used to facilitate sustained fission in a reactor. Heavy water is 10% heavier than ordinary water because it contains higher than normal proportion of deuterium, which is a form of hydrogen.

The heavy water surrounds the fuel bundles and slow 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 heavy water. The heated heavy water is pumped through the reactor to a set of boilers where it boils ordinary water to high pressure steam. While the heavy water is re-circulated back to the reactor, the pressure steam produced is transported through pipes to a large turbine where it pushes the blades and turn the shaft connected to a rotor in the generator causing the rotor to spin.

The spinning rotor is a large electromagnet that produces a rotating magnetic field. The field moves through a coil of copper wire, producing electricity that can be sent through transmission lines. Steam is condensed back into water using cooling water from the surrounding body of water.

Modern nuclear power stations use the same type of turbines and generators as the coal fired and hydroelectric power stations. Nuclear power plant costs about the same as coal powered plant but could be more expensive to install when compared to other forms of energy source. However, the cost of installing reactors have been consistently escalating for the past 3 decades (see the setbacks later on this page)

 

Advantages of Nuclear Energy

  • They 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 is a very reliable energy resource.


Disadvantages of Nuclear Energy

  • 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. The cost of installing nuclear reactors have been increasing by 15% every year for the past 30 years. Installing 1 reactor costs billions of dollars these days;

  • 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; and

  • Nuclear wastes or even the nuclear production material (e.g. Uranium pellets) can fall into the hands of those that would use them for destructive purposes. Nuclear energy is sometimes discouraged to minimize or prevent the proliferation of nuclear weapons.

 

All that has been discussed above are relevant to Nuclear Fission (i.e. nuclear energy from the splitting of atoms). There is also Nuclear Fusion which is the release of energy from the fusing together of the nuclei of atoms. 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. For in-depth discussion on both Nuclear Fusion and Nuclear Fission, we recommend that you get a copy of Clean Energy Fuels a book written by Dr. Dele Morakinyo one of the contributors to EnvironBusiness.



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