Реферат: Chernobyl Essay Research Paper April 26th 1986
Chernobyl Essay, Research Paper
April 26th 1986 marked the date of the worst nuclear accident to ever occur. Chernobyl, a nuclear power plant in Russia was undergoing routine safety tests that envolved running the reactor on less then full power, followed by a standard shut down. At Chernobyl’s reactor number 4 a specific test was designed to show that a coasting turbine could produce enough power to pump coolant through the reactor core while waiting for electricity from diesel generators.
During the test turbine feed valves were closed to initiate turbine coasting, and automatic control rods were withdrawn from the core. When the steam valves to the turbine close, the pressure in the reactor should go up causing the boiling point of the water to increase. This creates more water in the reactor, increasing cooling. During this test there was a problem with the feed water supply, so the increase in cooling water did not happen. What did happen was an uncontrolled increase in the steam pressure. The operator saw this and started to shut down the reaction by reinserting the control rods. The initial insertion of the control rods caused the reaction to concentrate in the bottom of the reactor. The reactor power rose well above its maximum capacity. Fuel pellets shattered, reacting with the cooling water, creating high pressure in the fuel containers. This surge in pressure caused the fuel containers to rupture. This led to two severe explosions, one a steam explosion, the other a rapid expansion of fuel vapor. The force of these explosions lifted the pile cap, allowing air to enter the reactor. The graphite used in the reactor construction caught on fire, ending a horrible and tragic sequence of events, but beginning another.
Local firemen, unaware of the dangerous amounts of radiation, were called in to put out the fire. All of the firemen died, either a result of the fire, or from breathing radioactive debris. Unfortunately, their heroic attempts were useless, because the core of the reactor was exposed making the fire much to hot for water to cool.
The first thing the Russians did was try to cover up the accident. This turned out to be impossible, considering the amounts of radioactive debris released into the air. Shortly after the accident a nuclear power plant in Sweden measured high amounts of radioactivity in their area, called the Russians to inquire if there had been an accident. The Russians shortly thereafter alerted the press, and evacuated towns surrounding Chernobyl.
This of course wasn’t their biggest problem. They needed to find the fuel that had escaped from the reactor in order to avoid another massive chain reaction. This was a huge problem due to the extreme amounts of radioactivity inside the sarcophagus. They didn’t have the money for robots, so they sent in the Soviet Army. 3400 men were used on “roof runs” in which they’d go and collect samples from the roof of the reactor. During these missions soldiers could be subjected to 20 Rankin’s of radiation. Many people who have worked at Chernobyl have died from sudden heart failure. The Russian government denies that this has anything to do with their work at Chernobyl, but their have been too many deaths related to heart failure for it not to be.
The next move was to find the fuel. Unlike American nuclear power plants that have their reactors over steel reinforced concrete the crazy Russians built their reactor on top of offices. Inside these offices radiation levels reach around 100 to 250 Rankin’s of radiation per hour. This means it would be impossible to ever work safely inside Chernobyl, unless of course you had a few hundred thousand years on your hands for the radioactivity to fall to safe levels. Unfortunately they didn’t, they had to find the fuel before another chain reaction occurred, releasing more nuclear fallout into the environment.
Throughout their early investigation they could find no clues to the whereabouts of the fuel. Finally, one cold December day in 1986, scientists came across a large highly radioactive mass approximately 2 meters across in size. Because of its unique shape they titled it the “Elephant’s Foot”. Their only dilemma was, what the heck is it? This problem probably would have been easy to solve if the Elephant’s foot wasn’t emitting 10,000 Rankins of radiation per hour. One of the scientists came up with the idea to shoot the “Elephant’s Foot” to obtain samples. Although they didn’t want to wreck the beauty of the “Elephant’s Foot” they decided it was a good idea (how pretty could solidified fuel be anyway?)
Due to the extreme bureaucracy of Russia’s government, finding a gun was much harder then one would assume. They first went to the army, only to be sent to the police, who sent them to the KGB, who sent them back to the police. They finally got a police man to come and shoot 30 rounds at the foot. They found that the “Elephant’s Foot” was composed of many layers and was made up of silicon dioxide mixed with fuel that had dripped from the reactors base.
Now that they had more of an idea about what they were looking for, they decided the next place to look was the core. It took them half a year to break through, and when they did they were shocked to learn it was completely empty. This was good news safety wise, but that still left everyone scratching their heads dumbfounded.
After the fuel shock, they decided to search the rooms under the reactor that were generating a lot of heat. They pooled all their money together and were able to buy a toy truck for 15 rubles (roughly $.52 at today’s exchange rate). Much to their dismay, the toy truck didn’t prove to be a wise investment, but it did detect a large mass that got them excited. They rigged up a camera dolly to go in, it found a lot of destruction, but no fuel. They had to go in themselves.
This time they were going directly under the reactor. This would be the most dangerous area they would investigate. What they found shocked them. Concrete was steaming from the floor, and below them they saw lava. They found some pretty crystals, they now call chernobalite, and learned that the lava was caused by nuclear fuel and sand.
Of course this wasn’t the end of their problems, what fun would that be? The inside of the sarcophagus was falling apart. If it collapsed, a whole lot of radioactive dust would escape into the air, and probably wouldn’t do much for the Russian’s popularity.
This was a big threat, the reactor could collapse any day so it needed immediate attention. They could burry it in concrete, but that would make it hard to monitor. They could cover it in sand, except sands a good insulator. Or they could build a 2nd sarcophagus, but that might cost more then 15 rubles. What they did know is that whatever they did had to last longer then the pyramids. They needed help from other countries.
Hopefully, with the knowledge learned from Chernobyl, and the rising need for nuclear energy, we can find a safer way run nuclear power plants.