Three Mile Island. The Three Mile Island accident was a partial meltdown of the Three Mile Island, Unit 2 (TMI-2) reactor on the Susquehanna River in Londonderry Township, Pennsylvania, near the Pennsylvania capital of Harrisburg. It began at 4 a.m.[2][3] on March 28, 1979. It is the most significant accident in U.S. commercial nuclear power plant history.[4] On the seven-point International Nuclear Event Scale, it is rated Level 5 – Accident with Wider Consequences.

It was still not clear to the control room staff that the primary loop water levels were low and that over half of the core was exposed. A group of workers took manual readings from the thermocouples and obtained a sample of primary loop water. Seven hours into the emergency, new water was pumped into the primary loop and the backup relief valve was opened to reduce pressure so that the loop could be filled with water. After 16 hours the primary loop pumps were turned on once again, and the core temperature began to fall. A large part of the core had melted, and the system was still dangerously radioactive.

"The China Syndrome"

It follows a television reporter and her cameraman who discover safety coverups at a nuclear power plant. "China syndrome" is a fanciful term that describes a fictional result of a nuclear meltdown, where reactor components melt through their containment structures and into the underlying earth, "all the way to China"