In the early hours of March 28, 1979, a pressure valve at the Three Mile Island nuclear power plant didn’t close as expected. It caused what is still considered a historic crisis in the history of nuclear power and caused countries around the world to reconsider their approach to it. Up to that point, the Pennsylvania plant had been considered to be at the forefront of the energy industry.
The pressure valve was what kept a reactor’s cooling water in place. When it failed to close, that contaminated water seeped into buildings across the facility. What created the real crisis was when employees mistakenly shut off the emergency water system because of problems with the control system. That meant the water pumps that would help dispose of the water didn’t kick on. On top of that, the reactor was off but still generating intense heat and nearing a meltdown that would result in radiation floating across the communities nearby.
Once the water began to leak into the area around the plant, the governor nearly ordered an evacuation (the plant was only 10 miles from the state capital Harrisburg), and did end up advising pregnant women and pre-school-age children to leave the five-mile radius around the plant, and for those within 10 miles to stay indoors. Over 100,000 people ended up fleeing.
Eventually, the situation stabilized, and the radioactive water and gas were contained. Plant workers were exposed to serious radiation, but nobody else was, and not one person died. The reactor, one of two at the facility, was damaged beyond repair.
There’s an interesting article with some helpful diagrams on the website of the Idaho National Laboratory, a research complex under the Department of Energy.
