Nuclear Power Plant Design

The Basic Design

Nuclear power plants have four vital parts of the electricity generation process; the fuel, the reactor, the turbine generator, and the coolant. These are all coupled with many other important components that allow for the control of the fission reaction, moving and storing spent fuel, fail safes in the event of a power outage, and the removal of steam. Here in the picture below, the design shows the necessary pipelines to move coolant, typically water, through the plant. This is important for the generation of steam and for regulating the temperature of the reactor.



Design Explanation

Inside the reactor, water is pumped around the fuel rods to remove heat. This contaminated water is then pumped through a pipe that transfers its heat into cooler water inside the steam generator. The steam from the steam generator rotates a turbine and generates electricity for use in the power grid (Marshall & Lamb, 2000).


The diagram also shows the intake from a body of water that is pumped into the building. The water is used to condense the steam after it has generated electricity. Once the condensing water has been heated to a high temperature, it is pumped into the cooling tower where it boils off into the atmosphere (Marshall & Lamb, 2000).

Fission

Fission is the core process of nuclear energy. It exploits unstable isotopes of uranium (which is uranium 235 and 238) to create heat. The reaction begins by irradiating uranium with neutrons. The excess neutrons cause the uranium to become unstable and the uranium splits into two separate atoms. Excess neutrons also break off as a result. These new neutrons will collide with more uranium atoms, furthering the reaction. The chain reaction continues and more heat is created (Nave, 2011). In order to stop the fission, a neutron absorbing material, such as cadmium, is placed between the fuel rods, slowing the reaction to a halt (Marshall & Lamb, 2000).


Uranium Extraction and Refining

The Mining Process

Mining uranium is similar to the extraction of other ores. Deposits near the surface can be strip mined, and deeper deposits can be mined from underground. Smaller deposits are accessed through in situ leaching, or, ISL. ISL works through highly oxygenated and weakly acidic or alkaline water is pumped through a confined aquifer, wherein uranium is held between sand. Uranium then leaches into the water and, the water is then pumped back to the surface for processing (Uranium Mining Overview, 2012).


The Refining Process

The uranium is refined through a series of chemical reactions. These chemical reactions are mainly acid treatment. The end product is a uranium oxide, or "yellow cake" for its yellow powder appearance. When the uranium is converted to fuel, the uranium oxide is packed into small ceramic pellets. These pellets are then stacked inside the fuel rods and are ready for use (Uranium Mining Overview, 2012).

Environmental Hazards

Meltdowns

The largest issue with nuclear power is the threat of a meltdown. Although they are very rare, the effects of catastrophic. A meltdown occurs when the external power source is cut off from the plant. This is important because it allows for operators to control the fission. When this happens, fail safes are put into use. Backup generators come online and generate electricity to stop the reaction. Then coolant is continually circulated into the reactor to regulate the temperature because the uranium does not stop producing heat immediately. If the backup generators fail or run out of fuel, then the reactor's temperature can reach incredibly high levels. The uranium can then melt the reactor itself and spill into the surrounding area. If it reaches oxygenated air, an explosion can occur, spreading radioactive material and fire (Matson, 2011). The environment around the plant is scarred with radiation after the meltdown, as the radiation levels will not decay for thousands of years.

Waste

Nuclear fission produces a variety elements and different isotopes as well. The more common products of fission are radioactive isotopes of Cesium, Strontium, Plutonium, Iodine, and Xenon. These materials have varying half-lives. Iodine's half life is 8 days, while Cesium has a half life of 30 years (Fission Fragments, n.d.). These waste products will continue to emit radiation that is harmful to the environment and to people. Currently, waste is stored on site for several years before being moved to a permanent storage facility. At the plant, they are stored underwater to trap radiation, but in the permanent locations they are typically contained inside a metal cylinder and buried beneath a layer of clay deep within the earth (Radioactive Waste Management, 2012) .


Findings from the Lab

The experiment performed in the lab was a failure, and did not demonstrate the effectiveness of nuclear waste containment procedures. However, if the experiment had succeeded, then the results would reflect the necessity of proper containment. The findings would demonstrate that nuclear waste cannot be simply buried, but must also be confined by a variety of materials to prevent toxic material from leaching into the groundwater. This is highly important, as radioactive isotopes of otherwise harmless elements can cause damage in the environment and humans. For example, Strontium, a safe mineral, has a harmful isotope, Strontium 90, that is a by-product of uranium fission. Strontium 90 can enter a person's body, build up in bones, and cause internal exposure to radiation (Fission Fragments, n.d.).


Personal Thoughts on Design

If I were to design my own nuclear plant, I would make certain of several things. First, that it was a fair distance away from civilians. Second, that it was not near any water supplies or sensitive ecosystems, and lastly, that it had fail safes to prevent meltdowns in the event of a black out. These would include backup generators, battery supplies to coolant pumps and reactor controls, and high quality containment procedures for the reactor and reactor waste. I would also test the viability of a turbine located on a higher level of the complex. The reactor would be on a lower level, and it would send steam to the upper levels. The steam would condense and fill a tank. The tank could be emptied, and the water allowed to flow around a second turbine, creating extra power.


References

Marshall, B & Lamb, R., (2000). Inside a nuclear power plant. Retrieved from http://science.howstuffworks.com/nuclear-power2.htm


Nave, R. (2011.). Retrieved from http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fission.html


Uranium mining overview. (2012). Retrieved from http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Mining-of-Uranium/Uranium-Mining-Overview/


Fission Fragments. (n.d.). Retrieved from http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fisfrag.html


Radioactive waste management. (2012). Retrieved from http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Nuclear-Wastes/Waste-Management-Overview/


Matson, J. (2011). Retrieved from http://www.scientificamerican.com/article.cfm?id=nuclear-energy-primer