Three Mile Island

Charlie Hopkins
July 17, 2015

Submitted as coursework for PH241, Stanford University, Winter 2015


Fig. 1: This figure shows the main feedwater pump which caused the partial meltdown. (Source: Wikimedia Commons)

The Three Mile Island disaster occurred on March 28, 1979. In the small town of Middleton, Pennsylvania, the Three Mile Island nuclear power plant experienced a series of electrical, human, and mechanical breakdowns leading to possibly the worst nuclear power plant accident in the history of the United States. Estimations have shown impacts in the natural ecosystems, due to radiation leakage, surrounding the nuclear reactor. As a result more than 50,000 people were evacuated from their homes following the mishap. [1] This accident occurring in the early stages of America developing nuclear energy, resulting in the general public opinion fearing nuclear energy and heightened regulations to ensure the safety of the public and environment.

The Accident

The accident began around 4:00 a.m., when there was malfunction in the secondary, non-nuclear section of the plant. The main feedwater pump became clogged and stopped working, which was caused by either a mechanical or electrical failure, preventing the steam generators from removing heat. This malfunction caused the turbine, and then the reactor to automatically shut down. The water pressure and temperature began to increase in the primary system, the nuclear portion of the plant, because the heat could no longer be transported to the secondary section. The pressurizer relief valve automatically opened, in order to stop the pressure from becoming excessive. After successfully decreasing the pressure by a certain amount, the pressure release valve should have routinely closed, but it did not. [2] Even though the valve was still open, indicators in the control room showed operators the valve to be closed. This caused a loss of coolant accident because of a significant amount of steam and water was still being released when it should have been cooling the primary section.


"The greatest of destructive forces can be developed into a great boon, for the benefit of all mankind. The United States knows the peaceful power from atomic energy is no dream of the future. The capability already proved, is here today." This was a part of President Dwight Eisenhower's famous Atoms for Peace speech in 1953. While nuclear energy can be a legitimate source of energy, there will always be a concern over the public's safety from the dangers of nuclear power plants. While the overall public opinion of nuclear power plants was negative after the accident, there was a six-month investigation ordered by Jimmy Carter, to investigate why the mishap occurred. [3] The findings stated that workers were operating under procedures that they were required to follow, but the control room was greatly inadequate for managing the accident. The accident breakdown at the plant also cause a significant amount of radioactive gas to escape into the environment, however many studies have shown no significant amount of harm to the people or animals in the area. Cleanup began in August 1979 and ended December 1993, with a total cost of around $1 billion. [4]

© Charlie Hopkins. 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. Gray and I. Rosen, The Warning: Accident at Three Mile Island (W. W. Norton, 2003).

[2] M. A. Lüsted, The Three Mile Island Nuclear Disaster (Essential Library, 2012).

[3] M. C. Hatch et al., "Cancer Near the Three Mile Island Nuclear Plant: Radiation Emissions," Am. J. Epidemiol. 132, 397 (1990).

[4] R. L. Goldsteen and J. K. Schorr, Demanding Democracy after Three Mile Island (U. Press Florida, 1991).