In Harrisburg, the capital of Pennsylvania in the eastern United States, flows a beautiful river called the Susquehanna. This river passes through Washington D.C., the U.S. capital, and empties into the Atlantic Ocean. Near Harrisburg, on this river, lies a small island called Three Mile Island, where a nuclear power plant was constructed beginning in 1968 and completed in 1974. At 4 a.m. on March 28, 1979, a nuclear reactor at the Three Mile Island plant suffered a meltdown due to a cooling system failure, resulting in a release of radioactive material. The reactor had only been in trial operation for four months, starting in December 1978.