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Three mile island accident

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Three Mile Island Accident: The Summary and Lessons Learned

On March 28 of 1979 a nuclear reactor meltdown occured at a power plant in Pensnsylvania, in the United States of America. The Three Mile Island nuclear power plant consisted of two separate nuclear reactors, TMI 1 and TMI 2. A series of events, starting at 4 a.m., escalated into the partial melting of the second nuclear reactor and the release of small amounts of radioactive gasses. (WNA 2001)

A pressurized water reacter consists of three separate continuous loops. Each loop has a pump circulating the coolant/water through it. The first loop contains the reactor, where nuclear fission takes place, which serves the purpose of heating the water. This loop also contains a pressurizer to keep the water in a liquid state, since temperaures far exceed 100 °C. This hot coolant then heats up cool water from the steam generator in the second loop, which turns a turbine to create electricity. Finally the third loop, which is connected to the cooling tower, provides cool water for the second loop's condenser. (Wikipedia, 2010)

The nuclear power plant accident began with a cease of functioning of the water pumps in the second loop of the reactor. As a result, there was no cool water in the steam generator to absorb heat energy from the coolant in the first loop. As the temperature inside the first loop increased, automated systems shut down both the turbine and the reactor. (NRC, 2009)

To offset an increase in pressure in the loop an automatic relief valve, attached to the pressurizer, opened releasing steam. Due to a mechanical fault, the valve did not close once the pressure had fallen. Instrumentation, showing that a signal to close the valve had been sent to the valve, led operators to assume the valve had been shut. (WNA, 2001) According to a source from the manufacturing company of the reactor, pressing the appropriate buttons in the control room would have shut the valve (Washington Post, 2010). Coolant continued to escape through the pressurizer, setting off emergency pumps to replenish the system with water. However, the water-level sensor located in the pressurizer showed high levels of water present. Operators assumed that this sensor reading represented the water-level in the entire system. In fact, coolant was diminishing in the system as it accumulated in the pressurizer while escaping through the open valve. In response to the water-level reading, operators began slowing down the emergency pumps and later turned them off. (WNA, 2001)

Temperature in the reactor continued to increase until the nuclear fuel and its cladding began to melt and pour into the coolant. By the time the accident was taken under control, half of the fuel had melted. Other than small amounts of radioactive gasses, all other radioactive materials were contained within the walls of the power plant. (NEI, 2009)

Immanuel Kant's duty ethics place strong moral value on the motives of an action rather than its results. Furthermore, moral actions arise from a sense of duty and not feelings or ambitions. (TheologicalStudies, 2004) If we focus on the nuclear plant operators, under this moral code, it is hard to place any fault on them. It seems that the operators worked to solve the problem to their full ability. Even though they made faulty assumptions, worsening the problem, it was a result of their training and ambiguity in their instrumentation. (WNA, 2001) There is no evidence to show that the engineers had ill or immoral intentions in their design. There were many working automated systems put into place to resolve the problems that arose. (Washington Post, 2010) However, it could be seen that the engineers did not fulfill their duty of designing a more user-friendly and descriptive control interface. (NEI, 2009)

To avoid this type of accident in the future, many changes and regulations have been put into place. With respect to the plant itself, changes included better building isolation, upgrading the automated systems used for plant shutdown and increased standards for system components. Improved instrumentation is also used. Changes regarding the employees have been made. New worker training programs and emergency protocols have been imposed. (NRC, 2009)

It is clear that the Three Miles Accident was a result of component failure and confusing instrumentation as well as a lack of adequately trained plant workers. However, new regulations have been implemented on nuclear power stations in the United States, which tackle these problems, to avoid any similar repetition. (NRC, 2009)

Reference List

Nuclear Energy Institute (NEI). http://www.cna.ca/english/pdf/nuclearfacts/NEI-TMI-Accident.pdf (accessed February 28, 2010), March 2009.

Nuclear Regulatory Commission (NRC). http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/3mile-isle.html (accessed February 27, 2010), August 11, 2009.

TheologicalStudies.org. http://www.theologicalstudies.org/articles/article/1527417/17142.htm (accessed March 1, 2010), November 20, 2004.

Washingtonpost.com. http://www.washingtonpost.com/wp-srv/national/longterm/tmi/stories/ch1.htm (accessed February 27, 2010).

Wikipedia: The Free Encyclopedia. http://en.wikipedia.org/wiki/Three_Mile_Island_accident (accessed February 28, 2010).

World Nuclear Association (WNA). http://www.world-nuclear.org/info/inf36.html (accessed February 28, 2010), March 2001.


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