The Chernobyl Disaster

On the 26th of April in 1986 one of the worst nuclear disasters in history occurred at the Chernobyl nuclear power plant in the Ukraine. The number 4 reactor at the Chernobyl Nuclear power plant ended up exploding after several errors that occurred during a scheduled safety systems test. The explosions released large amounts of radioactive materials into the sky and it was spread over great distances by wind streams. The repercussions of the disaster are only now being better understood today.

The reactor type at Chernobyl was a RBMK type reactor. The reactor is a vertically oriented reactor that uses graphite as an insulator which also caused problems due to the combustibility of the graphite that was used. "The reactor fuel is zirconium alloy clad uranium oxide enriched to 2.0% U-235" (Mosey). The RBMK reactor also has two 500MWt reactors which operate safely at 100% power of 1000MWt. "Reactor control is achieved by means of 211 boron carbide absorber rods" (Mosey). The purpose of the rods is to absorb the excess electrons in the core and to control the rate in which the reaction is taking place. At Chernobyl nuclear fusion occurred by bombarding an isotope of Uranium 235 with an electron thus causing it to become unstable and split into other radioactive elements and at the same time releases a great amount of energy that we harness, and several electrons which continue the reaction.

"The test involved using the residual energy of the turbogenerator as it ran down to provide electricity for the main circulating pumps to reduce the time the pumps would be without power following a postulated loss of electrical power" (Mosey). Initially they decreased the power of the reactor to 50% power and isolated the ECI (emergency coolant injection system for a period of 22 hours and during this portion of the test everything checked out alright. After they had completed that portion of the test they decreased the power even farther to about 20-30% of full power. "The Reactor was then operation at around 720 MWt which was planned fore the test. Operation of the reactor below this level is very inadvisable because of instability, but not prohibited" (Mosey). Shortly there after due to equipment failure the power output dropped to 30Mwt. The operators feared that the reactor would go offline and the test would end so they attempted to raise the power back up so they could continue with the test. After several small adjustments by the operators they were able to bring the power back up to 200MWt and stabilize it. In order to raise the power they tried to remove several rods in order to increase the reaction. "At this point it is thought that all but six control rods had been removed from the reactor core Ð'- the minimum safe operating number was considered to be 30" (The Chernobyl Disaster). The normal operation power of the Reactor was 1000MWt and at this point in time the power jumped to about 100 times the normal operating power level. The first explosion occurred at this time and it was caused by steam in the reactor which blew the top off the reactor and a hole in the roof the second explosion was that of the hydrogen that was generated in the reactor through the fusion process. After the disaster the Soviet Union attempted to cover up the disaster and contain the radioactive materials from the reactor which were exposed.

During the second explosion it blew radioactive debris into the atmosphere and it was spread out throughout Europe carried by the wind streams. "The Disaster released at least 100 times more radiation the atom bombs dropped on Nagasaki and Hiroshima" (The Chernobyl Disaster). The Fire over the reactor was dealt with by dropping a total of 5000 Tons of materials from helicopters including boron carbide, dolomite, and clay and sand. These materials were able to smother the fire and greatly reduce radioactive emissions. "Much of the fallout was deposited close to Chernobyl, in parts of Belarus, Ukraine and Russia. More than 350,000 people resettled away from these areas, but about 5.5 million remained" (The Chernobyl Disaster). Many people around the area today are incapable of leaving due largely to economic problems that the disaster has caused in the area. The people in that area have been exposed to large amounts of radiation also due to the explosions.

"The most obvious health impact is a sharp increase in thyroid cancer. About 4,000 cases of the disease have been seen, mainly in people who were children or adolescents at the time" (The Chernobyl Disaster). The total amount of thyroid cancer cases is also expected to increase as time goes on. Due to the increased levels of radiation it has also caused a large increase in