Why was Three Mile Island important

GAU and super-GAU

1979, "Three Mile Island" - the first GAU

Due to the normal operation of a nuclear power plant, the exposure to radioactive radiation is rather low, so that at the beginning of the use of atomic energy, devices for switching off the reactors were virtually the only safety precautions.

Improvements came with a US concept that specified the sudden break in a main coolant line as a disaster. The emergency cooling and the outer protective shell of the reactor building - a large covering made of metal or concrete - thus became common safety systems.

In 1979 the American nuclear power plant "Three Mile Island" (Pennsylvania) suffered the first meltdown. The fuel rods could no longer be cooled and the so-called core meltdown began.

When the core melts, the fuel rods in the power plant heat up so much that they melt and there is a risk of an explosion. However, this did not occur in the American power plant. The dangers of radioactive substances escaping for the population remained relatively low.

Super-GAU = nuclear power plant out of control

If, on the other hand, a reactor disaster is no longer controllable, one speaks of a worst-case scenario. In April 1986 he entered Chernobyl in what is now Ukraine. During an experiment, Unit 4 of the nuclear power plant got out of control. The heat bent metal and reactor rods and the core could no longer be cooled. As before in "Three Mile Island" there was a meltdown.

In Chernobyl, however, the situation could no longer be brought under control. As a result of the explosion that followed, 1,500 tons of graphite caught fire inside the reactor. A real firestorm tore radioactive materials miles high into the atmosphere, where they were caught by strong winds. The radioactive cloud spread contaminated material over large parts of Europe.

It is estimated that 600,000 people were exposed to high levels of radiation, and around 7,000 were killed among the rescue teams. According to information from the World Health Organization, 125,000 helpers fell seriously ill. An area half the size of the Federal Republic was contaminated in the Ukraine, Belarus and Russia. 375,000 residents had to be relocated. 3.5 million people are officially registered as victims of the accident in Ukraine alone.

The terms GAU and Super-GAU are actually outdated. The International Assessment Scale for nuclear events has existed since 1990, classifying accidents and nuclear accidents more precisely. The scale ranges from level 0 to level 7. Level 0 denotes an event with little or no safety-related significance.

Levels 1 to 3 designate incidents from minor to serious. Levels 4 to 7 describe accidents of various intensity. So far, only two accidents have been classified in the highest level: the destruction of the Chernobyl nuclear reactor in 1986 and the Fukushima nuclear disaster in 2011.

The causes of the Chernobyl disaster

In Chernobyl, various circumstances were responsible for turning the GAU into a super-GAU. The graphite fire, which spread the radioactive substances over a wide area, was later described as the most serious feature of the accident.

According to the official version, a number of human errors led to the accident. On the day of the accident, the technicians of the power plant wanted to carry out a turbine test with the reactors still running and shut down the automatic control system and the emergency cooling.

In addition, the power plant had no protective cover around the reactor building that could have prevented or limited the escape of radioactive material.

Author: Silke Rehren