Background: Chernobyl Disaster
The Chernobyl power plant is located in Pripyat, Ukraine. The plant consisted of four reactors, which began operation between 1978 and 1984. On April 26,1986, engineers decided to run a test to determine how long the reactor would be provided with sufficient cooling water during a complete loss of power to the large generating complex while the emergency cooling system is inoperable. According to the electrical engineers calculations, the inertia of the nuclear plant’s 500 MW electric turbines would generate enough electricity to keep the water pumps operating during the 30 to 50 second delay that is required to start the emergency diesel generators. However, the electrical engineers were not specialized in nuclear reactors and did not consult efficiently with other nuclear reactor specialists about the procedure.
To conduct this experiment, the engineers had to disable the reactor's safety systems. This included turning off important automatic safety controls and removing control rods (absorb neutrons and limit the reactions). During the experiment, less cooling water entered the reactor and began to turn to steam. The reaction increased to dangerous levels as less coolant and control rods were available. To counteract the dangerous reaction, the engineers tried to reinsert the remaining control rods but due to the design flaw in the graphite tips it resulted in the displacement of the coolant. As the graphite tips displaced the coolant, the reaction increased drastically due to the heat while getting rid of more coolant. This resulted in an eruption of power surging through Chernobyl, Ukraine that destroyed unit 4 of the nuclear power station. Due to violations of safety regulations, the operators switched off controls systems that allowed the reactor, which was flawed, to reach unstable conditions. A sudden power surge caused an explosion that ruptured the reactor vessel, which destroyed the reactor core and severely damaged the reactor building.
The workers failed to consider that RBMK-1000 reactors (the reactors used at Chernobyl) could develop positive void coefficient reactivity. In summary, positive void coefficient reactivity is when increasing boiling is caused by increasing core temperatures that can lead to an increase in core reactivity and an increase in core power. The development of positive void coefficient reactivity accelerated the causation of a steam explosion. Usually, this positive feedback mechanism is avoided in reactor plants.
Ultimately, the Chernobyl disaster caused physical and psychological disruption due to the emission of massive amounts of radio nuclides that were measurable in all countries of the northern hemisphere. In response to the catastrophe, emergency crews used helicopters to pour sand to stop the fire and additional releases of radioactive material and boron to prevent more nuclear reactions from occurring. Weeks after the accident, the emergency crew covered unit 4 with the “Sarcophagus” to contain further release of radioactive material and the burial of a square mile of pine forest near the plant to reduce further contamination. Also, officials closed off the area within 19 miles of the plant and the Soviet government evacuated 115,00 people from heavily contaminated areas and 220,000 more people after 1986. Ultimately, the disaster caused adverse health effects that created 6,000 cases of thyroid cancer in children and other health effects that would psychologically harm those affected in the future.
To conduct this experiment, the engineers had to disable the reactor's safety systems. This included turning off important automatic safety controls and removing control rods (absorb neutrons and limit the reactions). During the experiment, less cooling water entered the reactor and began to turn to steam. The reaction increased to dangerous levels as less coolant and control rods were available. To counteract the dangerous reaction, the engineers tried to reinsert the remaining control rods but due to the design flaw in the graphite tips it resulted in the displacement of the coolant. As the graphite tips displaced the coolant, the reaction increased drastically due to the heat while getting rid of more coolant. This resulted in an eruption of power surging through Chernobyl, Ukraine that destroyed unit 4 of the nuclear power station. Due to violations of safety regulations, the operators switched off controls systems that allowed the reactor, which was flawed, to reach unstable conditions. A sudden power surge caused an explosion that ruptured the reactor vessel, which destroyed the reactor core and severely damaged the reactor building.
The workers failed to consider that RBMK-1000 reactors (the reactors used at Chernobyl) could develop positive void coefficient reactivity. In summary, positive void coefficient reactivity is when increasing boiling is caused by increasing core temperatures that can lead to an increase in core reactivity and an increase in core power. The development of positive void coefficient reactivity accelerated the causation of a steam explosion. Usually, this positive feedback mechanism is avoided in reactor plants.
Ultimately, the Chernobyl disaster caused physical and psychological disruption due to the emission of massive amounts of radio nuclides that were measurable in all countries of the northern hemisphere. In response to the catastrophe, emergency crews used helicopters to pour sand to stop the fire and additional releases of radioactive material and boron to prevent more nuclear reactions from occurring. Weeks after the accident, the emergency crew covered unit 4 with the “Sarcophagus” to contain further release of radioactive material and the burial of a square mile of pine forest near the plant to reduce further contamination. Also, officials closed off the area within 19 miles of the plant and the Soviet government evacuated 115,00 people from heavily contaminated areas and 220,000 more people after 1986. Ultimately, the disaster caused adverse health effects that created 6,000 cases of thyroid cancer in children and other health effects that would psychologically harm those affected in the future.
1. "Backgrounder on Chernobyl Nuclear Power Plant Accident." NRC. Web. 1 Dec. 2014.
<http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/chernobyl-bg.html>.
2. "Chernobyl Accident 1986." Chernobyl. World Nuclear Association. Web. 1 Dec. 2014.
<http://www.world-nuclear.org/info/Safety-and-Security/Safety-of-Plants/Chernobyl-Accident/>.
<http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/chernobyl-bg.html>.
2. "Chernobyl Accident 1986." Chernobyl. World Nuclear Association. Web. 1 Dec. 2014.
<http://www.world-nuclear.org/info/Safety-and-Security/Safety-of-Plants/Chernobyl-Accident/>.