What was the chernobyl accident?On April 25, 1986, reactor number four should be routinely discontinued in connection with scheduled maintenance. Chief Engineer Nikolai Fomin took the opportunity to test a security procedure. He wanted to investigate whether the turbines of the reactor could produce enough energy to keep the cooling pumps running until the diesel-powered emergency generator was activated in the event of a failure of the plant’s external power supply. This particular emergency supply was crucial for keeping pumps that delivered cooling water to the reactor. In order to prevent the attempt to be interrupted, the security systems of the nuclear installation were turned off. This attempt was the start of the world’s largest nuclear power plant disaster.
How did the experiment proceed?
What was caused by the Chernobyl accident?
It has been difficult to determine the causes of the Chernobyl accident, especially because the nuclear energy producing countries were very bad at informing each other about the experiences with nuclear power. This meant that one could not benefit from each other’s knowledge. Therefore, a wide range of eyewitness reports and experimental reconstructions have been necessary to get an idea of the cause of the accident.
The background to the accident is believed to be a combination of human errors and technical defects in the reactor. According to the website www.chernobyl.info (see sources), the reactor type used by the Chernobyl engine has an error in the control rods. In a reactor, the energy level is normally controlled by lifting and lowering the control rods so that the fewer control rods that are between the core elements, the greater the power of the reactor. However, in reactor number four at the Chernobyl plant, there was a fatal mistake in this process. This meant that when the control rods were lifted and quickly lowered again, the effect was completely opposite, namely that the reactor power was increased. If “too many” control rods are lifted at one time and then lowered simultaneously in an emergency, as in Chernobyl, the energy level apparently rises so dramatically that the reactor is destroyed.
What did you do to slow the fire in reactor 4?
The first ten hours after the accident, fire extinguishers pumped cold water into the heart of the reactor to extinguish the fire and stop the discharge of radioactive materials. However, the effect was minimal. Because of the high temperatures the graphite burns, it can not be switched off with water or with chemical extinguishing media. Therefore, you had to put in more powerful shooting.
From April 27th to May 5th, more than 30 helicopters flew over the burning reactor and dropped more than 2400 tons of lead and 1800 tons of sand to quench the fire and absorb the radioactive radiation. However, this only worsened the situation. The heat was increased under the dumped materials and the temperature in the reactor rose again. This meant that the amount of radioactive radiation was increased. Therefore, the tactics had to be changed again and in the final phase of the fire extinguisher the reactor was cooled with nitrogen.
On May 6, both the fire and the radioactive release were finally under control. According to www.chernobyl.info (see sources).