After the magnificent discovery of nuclear reactions in the last century, Albert Einstein, one
of the greatest thinkers of those times, once remarked, “There is not the slightest indication that
nuclear energy will ever be obtainable.”
Nowadays, despite this brave prediction, humans take full
advantage of this energy source at no surprise to anyone; yet, many still question whether this
advancement is absolutely safe to our health and environment, and these beliefs are not
unreasonable. One of the largest impacts on people and the industry was made by the nearly
catastrophic Three Mile Island nuclear accident that occurred near Middletown, Pennsylvania, USA.
In the early morning of March 28, 1979, the Unit 2 (TMI-2)
of the plant experienced a
major failure: the central feed-water pumps stopped functioning, preventing heat removal from the
steam generators. The turbine and the reactor shut down, increasing the pressure inside the
pressurizer. Automatically, the relief valve opened, but got stuck-open once the pressure stabilized.
The malfunction was not noticed by the operator, and the coolant poured out of the valve, causing
core overheating. Meanwhile, the control room indicators were not able to show the actual level of
coolant water in the reactor core; the operators could only see the level of water in the pressurizer
which was unallowably high, and because of that, they wrongly supposed that the core was fully
covered with water. There still was no visible indication that the relief valve was open. Not being
able to identify the loss-of-coolant situation, the operators turned off the automatic emergency-
cooling system and almost all of the emergency pumps, reducing the flow of coolant through the
core even more.
Without cooling, the fuel casing material reacted with the steam and produced
hydrogen which then escaped into the containment structure and exploded. This, fortunately, did not
lead to a breach in the containment walls.
The nuclear rods overheated and the pellets began to
melt. Next shift’s crew arrived and managed to block the relief valve, then contacted Babcock &
Wilcox and the Nuclear Regulatory Commission (NRC),
however, for the latter one, they could
only leave a message. The regional office sent the first team of inspectors to the site and, as the
radioactivity levels were already raising, all but essential personnel was ordered to leave the plant.