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| Fig. 1: A crowd of concerned citizens in Harrisburg, Pennsylvania vouching for solar energy opposing nuclear energy to ensure their safety. (Source: Wikimedia Commons) |
In Central Pennsylvania there is a nuclear power plant site called Three Mile Island. On March 28, 1979, one of the worst nuclear accidents in U.S. history occurred there. An unfortunate series of human and mechanical errors led to the atmosphere being filled with dangerous radioactive gases. [1] Approximately 50,000 people were forced to evacuate their homes after the incident and today, the power plant is inactive and was permanently shut down. [2,3] Te accident greatly increased public apprehension over nuclear power. Very few nuclear power plants have been built in the U.S. since then. [1]
Early in the morning on the day of the incident an electrical or mechanical failure caused a main feedwater pump to clog up, malfunction and stop working. [2] Heat wasn't being removed and the reactor then shut down. The main water feed pumps were prevented from sending water to the steam generators and the water pressure and temperature immediately began to increase. [3] The problem was that these numbers increased on the nuclear side of the plant and in response a valve that was made to help relieve pressure automatically opened. The pressure numbers went down successfully and when that happens usually the valve should have closed, but it was stuck open and the staff was unaware of the cooling water still pouring out. [3] After this had occurred, unfortunately careless decisions were made that people thought would help solve the problem, but instead made it worse. [4] They thought that the problem would be solved by restricting the amount of emergency cooling water being pumped into the primary system, but this was wrong, and the most dangerous kind of nuclear of power accident was caused as the reactor core ended up overheating at 2400°K and melting. [3,4] Significant amounts of radioactive gas did find their way into the atmosphere. Thankfully, studies have shown that no major harm was done to people living in the neighboring area. 2 million people were exposed to a harmelss dose of about 1 millirem on average. [2,4] The cleanup of it all took 14 years and had a total cost of around $1 billion. [4]
Unfortunately, a combination of mechanical deficiencies and human error caused a terrible nuclear accident at the Three Mile Island. This permanently changed both the nuclear industry and how the Nuclear Regulatory Commission (NRC) regulates nuclear power plants. [4] Because this situation occurred, some people started to question their safety (see Fig. 1). In response the NRC strengthened regulations. [3] This includes more stringent equipment requirements and upgraded designs, for example to improve fire protection and the reliability of the pressure relieve valves. [4]
© Bryce Wills. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] M. Stencel, "A Nuclear Nightmare in Pennsylvania," Washington Post, 27 Mar 99.
[2] C. Hopkins, "Three Mile Island," Physics 241, Stanford University, Winter 2015.
[3] "Three Mile Island Accident," U.S. Nuclear Regulatory Commission, June 2018.
[4] M. Joshua, "The Three Mile Island Accident and its Impact on Nuclear Power Plant Regulations," Physics 241, Stanford University, Winter 2018.