When they forced the resin out, a small amount of water forced its way past a stuck-open check valve and found its way into an instrument air line. The operators decided to blow the compressed air into the water and let the force of the water clear the resin. These filters are designed to stop minerals and impurities in the water from accumulating in the steam generators and decrease corrosion rates on the secondary side.īlockages are common with these resin filters and are usually fixed easily, but in this case, the usual method of forcing the stuck resin out with compressed air did not succeed. The initial cause of the accident happened eleven hours earlier, during an attempt by operators to fix a blockage in one of the eight condensate polishers, the sophisticated filters cleaning the secondary loop water. 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 nighttime 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 Cleanup started in August 1979, and officially ended in December 1993, with a total cleanup cost of about $1 billion. However, epidemiological studies analyzing the rate of cancer in and around the area since the accident determined there was not a statistically significant increase in the rate and thus no causal connection linking the accident with these cancers has been substantiated. 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 a cacophony of alarms, an inconvenient arrangement of instruments and controls, and the absence of clear indicators for coolant inventory 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 in Pennsylvania.
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