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On April 26, Chernobyl Chernobyl On April 26, 1986, two explosions occurred at the nuclear power plant located in the USSR. Massive amounts of radiation were released. It contaminated the immediate surrounding areas. Then spread to surrounding countries quickly. The radiation affected several aspects of life including the countries both human and animal populations, as well as the economy. On the night of April 25, 1986, plant employees were preparing for a series of experiments to be performed on the number four reactor at the Chernobyl nuclear power station in the Soviet Ukraine (Medvedev).
Reactor four was scheduled for its annual maintenance check. At this time, arrangements had also been made for the experiments to be done to test how long the power stations steam turbine could generate electricity after its steam supply had been shut off. The station had backup diesel generators for just such an occasion but they took a long time to get up and running. Similar tests had been done in 1982 and 1984 but had shown that the electricity produced without the steam from the turbines was not enough to support the safety systems of the plant before the diesel generators could kick in (Medvedev). The power station officials saw the need for the power during that incident if it may occur. New equipment had since been installed today to correct the problem.
This was a perfect time for the experiment because the reactor would have to be running at reduced power for the maintenance and tests both. The technician who drew up the plans for the experiment didnt discuss them with any of the physicists, engineers, or any other of the nuclear safety staff at the plant. Although no authorization for the tests was given, the tests proceeded anyway. The first serious error of the people involved in the testing was the shutoff of the emergency core cooling system (Hawkes p. 99).
This meant the reactor would be without one of its most important safety systems. When things started going wrong, operators overrode one safety system after another to try to correct their own mistakes, any one of the safety systems may have prevented the accident from happening. At 1: 00 a. m.
on Friday, April 25, operators began to power down the reactor. The desired level of power for the reactor to perform the tests was between 700 and 1000 MW. The reactors power was originally at 3200 MW. By 12: 00 p. m. the reactor had dropped down to 1600 Many at 2: 00 p.
m. they switched off the emergency cooling system for the reactor (Hawkes p. 100). Operators then received a call from a grid controller in Kiev. He said he needed the reactors power for several more hours and told them to stop reducing the reactors power. They obeyed, but forgot to turn the emergency cooling system that they had turned off back on. At 11: 10 the controller called back and said he no longer needed the power, so the operators then proceeded to continue powering down the reactor.
At 12: 28 a. m. on Saturday April 26, the operators made another serious mistake. They set a regulator setting incorrectly. As a result of the incorrect regulator setting, the reactors power crashed to 30 MW instead of the desired 700 to 1000 MW (Hawkes p. 100). At that point, the operators tried to rescue the reactor.
They knew the power was too low perform the test, but also knew that if they abandoned it then they would have to wait another year before the test could be tried again. (The reactor received annual maintenance every year. ) By then they had another problem on their hands. It was called Xenon poisoning. Xenon- 135 isa gas produced in nuclear fission that absorbs electrons (Hawkes p. 101). If a reactor is running at full power, there are enough neutrons to control the xenon gas produced during fission. Since the reactor was at very low power, Xenon gas became dominant over the limited neutrons.
To cope with the Xenon-poisoning problem, the operators started pulling control rods out of the reactor. One of the plants operating rules states that there should never be less than 30 control rods in the reactor at one time. The operators had removed 23 of the control rods leaving only 7 in the reactors core (Hawkes p. 101). At 1: 00 a. m.
the power had climbed back to 200 MW, but was still well below the correct level for the tests. The operators then made another big mistake. They turned two more pumps to circulate water to the reactor core to join the six that were already in use. Because of the low power to the reactor, the water caused an extremely unstable balance in the water and steam levels. The levels began changing unpredictably from second to second, and the operators could not control it. At 1: 20 a.
m. in response to the water levels that were dropping below the emergency mark, they blocked the automatic shutdown system that would normally have closed down the reactor. At 1: 23 a. m. they thought they had everything under control, and started the experiment. They began by shutting off the last safety system that would have come into operation automatically when the turbines shut off.
The reactor was now running free. Its control rods were out and its safety systems were turned off. The shift manager immediately knew something was wrong, and yelled at one of the operators to press button AZ- 5. This should have driven all of the control rods into the core, but the rods were already distorted from the heat, and did not fall into place.
During the last seconds before the explosion, the core went critical. Its power went from seven percent to several hundred times the normal level. Then the reactor exploded. This was very similar the explosion of an atomic bomb. The main difference between this explosion and one of a nuclear bomb is the speed at which it happens. In a bomb, the reaction goes much faster, taking only a few billionths of a second.
The whole thing still happened so fast that the fuel didnt have time to ignite or even melt. It just shattered into fragments. Four seconds after the first explosion, another explosion went off. The cause of this explosion is unknown. This explosion blasted the 1000 -ton lid off of the reactor and brought a 200 -ton refueling crane onto the core of the reactor. Eventually, more reactions took place inside the reactor, which started fires in 30 different places including several on the tar roof of the power station.
Blocks of graphite on the reactor soon caught fire and produced a cloud of extremely radioactive products including lanthanum- 131, ruthenium- 103, calcium- 137, iodine- 131, tellurium- 132, strontium- 89, strontium- 90 and yttrium- 91. The cloud escaped from the huge hole in the roof, and into the atmosphere (Gale). Warnings were sounded after the second explosion, and nearby firefighters raced to the power station. As soon as Chernobyl fire chief Leonid Telyatnikov arrived at the scene of the explosion he saw 28 firefighters already there. The flames were trying to spread to reactor number 3. Telyatnikov led one group of his men to the highest part of the station roof where the turbine section stands 69 meters above the ground where the most serious fires were.
All firefighters knew of the radiation levels they were being exposed to, but none of them moved from their posts. This showed extreme courage from the Soviet firemen. They knew the fire had to be fought no matter what the consequences were. If the fire reached reactor number 3 it could cause another explosion like the first two. Soviet authorities then attempted to smother the fire with massive amounts of sand, clay, lead, and boron dropped from helicopters (Rickard p. 19).
The radiation levels were so high that each helicopter pilot was only allowed to fly 22 missions, and in the end 5, 000 tons of material were dumped onto the plant. To prevent the core from burning its way down into the earth and contaminating water supplies, 400 engineers tunneled beneath the reactor. They then poured in concrete to make a thick, heatproof platform underneath the core (Rickard p. 19). Eventually, engineers got the fires at the power plant under control.
Emergency teams took turns entering the most dangerous areas, using stopwatches to time how long they were exposed to high levels of radiation. Remote controlled vehicles and protected manned vehicles were used to clear debris inside the plant. Walls and ditches had to be built to keep water from draining out of the plant into the Pripyat and Dnieper Rivers that supply most of Kiev's water. Vast areas of contaminated topsoil were removed and the roofs of houses in nearby Pripyat were hosed down to remove radioactive material from them (Rickard p. 18). The final stage of the cleanup process was the construction of an enormous concrete shell to house the entire reactor. It was built with ventilation shafts containing sensors to monitor the levels of radiation inside the destroyed core of the reactor (Rickard p. 14).
Finally, Soviet leaders began to release information about the disaster to the rest of the world and started accepting the offers from foreign governments and experts. Protective suits from Britain and remote controlled vehicles from West Germany were used to clean up the site. Some American surgeons flew to Moscow and Kiev to treat the people who were most seriously affected by the radiation. Unfortunately for some of them, there was nothing that could be done towel them.
One American doctor predicted that over 100, 000 soviets would need special check-ups for the rest of their lives (Rickard p. 19). It would be necessary to watch out for signs of cancer and or any other sicknesses that may have been caused by the massive amounts of radiation received. The fallout produced from the explosion at the nuclear power plant in Chernobyl was carried by winds across Europe in only seven days. Maps had been drawn up three months after the explosion that showed where the most contaminated areas in Europe were.
Those maps however were not released until March 1989, and were nearly useless by the time they were released (Norman) The economic cost of the accident is still not fully calculated. It was recently stated thatcher was a direct cost of 4 billion rubles (about $ 6. 8 billion) (for example, loss of the reactor, relocations, medical care, and food surveillance). With additional costs within other countries, the total may be some were around $ 15 billion to asses the damage. (Anspaugh p. 1513). Anspaugh, Lynn R. , Robert J.
Catlin, and Marvin Goldman. The Global Impact of the Chernobyl Reactor Accident. Science 16 December 1988: 1513. Gale, R.
and Hauser A. (1988). Final Warning: The Legacy of Chernobyl. New York: Warner Books. Medvedev, Grigori. (1991). The Truth About Chernobyl. Basic Books.
Norman, Colin and David Dickenson. The Aftermath of Chernobyl. Science 12 September 1986: 1141. Rickard, Graham. (1989). The Chernobyl Catastrophe. New York: The Book wright Press.
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