EST in TMI-2's secondary loop, one of the three main water/steam loops in a pressurized water reactor (PWR).
The main chain of events leading to the partial core meltdown on Wednesday March 28, 1979, began at 4:00:37 a.m.
In the night hours before the incident, the TMI-2 reactor was running at 97% power, while the companion TMI-1 reactor was shut down for refueling. Simplified schematic diagram of the TMI-2 plant The decommissioning is expected to be completed in 2079. Meanwhile, TMI-1 was shut down in 2019 due to operating losses and is being decommissioned at an estimated cost of $1.2 billion. Ĭleanup at TMI-2 started in August 1979 and officially ended in December 1993, with a total cost of about $1 billion (equivalent to $2 billion in 2021). Due to the nature of such studies, a causal connection linking the accident with cancer is difficult to prove. Some epidemiological studies analyzing the rate of cancer in and around the area since the accident did determine that there was a statistically significant increase in the rate of cancer, while other studies did not. The partial meltdown resulted in the release of radioactive gases and radioactive iodine into the environment.Īnti-nuclear movement activists expressed worries about regional health effects from the accident.
It has been cited as a contributor to the decline of a new reactor construction program, a slowdown that was already underway in the 1970s. The accident crystallized anti-nuclear safety concerns among activists and the general public, and resulted in new regulations for the nuclear industry. During the event these inadequacies were compounded by design flaws, including inconveniently arranged instruments and controls, the use of multiple similar alarms, and a failure of the equipment to clearly indicate coolant inventory level or the position of the stuck-open PORV. TMI training and procedures left operators and management ill-prepared for the deteriorating situation. The mechanical failures were compounded by the initial failure of plant operators to recognize the situation as a loss-of-coolant accident (LOCA). The accident began with failures in the non-nuclear secondary system followed by a stuck-open pilot-operated relief valve (PORV) in the primary system that allowed large amounts of nuclear reactor coolant to escape. On the seven-point International Nuclear Event Scale, it is rated Level 5 – Accident with Wider Consequences. It is the most significant accident in U.S. 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.
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