Properties of Matter | Three mile Island Project | 5/6

How it Starts

The most serious atomic power reactor disaster in the United States began very early on the morning of March 28th, 1979, when the main feed-water pumps malfunctioned and stopped pumping water to the steam generators of Reactor Number 2.

The reactor automatically shut down due to its loss of feed-water, but the temperatures continued to rise. The backup cooling system had been improperly locked closed and could not provide cooling water to the atomic reactor. Without cold water being pumped to the steam generator, pressure and temperature began to increase. A pressure-relief valve automatically opened as it was designed to do and the pressure levels dropped, but due to a mechanical failure, the valve did not shut properly. Due to this mechanical failure Steam continued to escape the reactor, soon the water that submerged the Nuclear Rods began to boil off, exposing the Rods to air. This was the start of the meltdown.

Radioactive Material Released

Radioactive gases from the reactor cooling system built up in the makeup tank in the auxiliary building. During March 29 and 30, operators used a system of pipes and compressors to move the gas to waste gas decay tanks. The compressors leaked, and some radioactive gases were released to the environment. These went through high-efficiency particulate air (HEPA) filters and charcoal filters which removed most of the toxic air, except for the noble gases, the estimated total of which was about 370 PBq  With short half-life, these did not pose a health hazard.

Radioactive Material Released

What happened:

  • After shutting down the fission reaction, Tower Number 2 reactor’s fuel core became uncovered and more than one third of the fuel melted.
  • Inadequate instrumentation and training programs at the time hampered operators’ ability to respond to the accident.
  • The accident was accompanied by communications problems that led to conflicting information available to the public, contributing to the public’s fears
  • A small amount of radiation was released from the plant. The releases were not serious and were not health hazards. This was confirmed by thousands of environmental and other samples and measurements taken during the accident.
  • The containment building worked as designed. Despite melting of about one-third of the fuel core, the reactor vessel itself maintained its integrity and contained the damaged fuel.

    Longer-term impacts:

    • Applying the accident’s lessons produced important, continuing improvement in the performance of all nuclear power plants.
    • The accident fostered better understanding of fuel melting, including improbability of a “China Syndrome” meltdown breaching the reactor vessel and the containment structure.
    • Public confidence in nuclear energy, particularly in USA, declined sharply following the Three Mile Island accident. It was a major cause of the decline in nuclear construction through the 1980s and 1990s.