The Chernobyl Nuclear Reactor Meltdown
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During the test turbine feed valves were closed to initiate turbine coasting, and automatic control rods were withdrawn from the core.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. ...