Читать книгу Industrial and Medical Nuclear Accidents - Jean-Claude Amiard - Страница 40

On March 28, 1979, one of the two generating station’s reactors at Three Mile Island (TMI-2) in Pennsylvania (United States) suffered serious damage. These were 900 MW-pressurized water reactors. They were located on a small island (3.3 km²) in the Susquehanna River near Harrisburg. The cause of the accident was a result of the leakage of the primary water circuit enclosure (second protective barrier) because of a pressurizer relief valve that remained blocked in the open position. As a result, the core was no longer cooled, resulting in the melting of a substantial part of the fuel. The containment, the third barrier, played its role with the exception of a slight radioactive release that is difficult to quantify [IRS 12c]. This accident was classified as a level 5 accident on the INES.

Further analysis [NSA 80] showed that serious damage to the reactor fuel did not begin until about 1 hour and 40 minutes after the accident. During the accident, water containing radioactivity was removed from the reactor building at various times. Some of the radioactive gases dissolved in this water spread into the atmosphere of the auxiliary building and dispersed in the vicinity of the plant through the auxiliary building’s ventilation system.

Six years after the accident, it was possible to enter the enclosure, and a camera introduced into the tank showed that a significant portion of the fuel had melted (45%) and that it had partially flowed (20%) to the bottom of the tank but had not passed through it. The corium (the lava-like mixture of material created during the nuclear meltdown) had stratified at the bottom of the tank without causing an explosion.

Currently [NRC 11], the damaged core has been completely removed from the tank, including the parts melted during the accident; the containment has also been cleaned, and the plant is awaiting a decision on its future that could potentially be a complete dismantling, making the current right-of-way usable.