...Continuation from Part 2
During the days following the accident, hundreds of people worked to quell the reactor fire and the escape of radioactive materials. Liquid nitrogen was pumped into the reactor core to cool it down. Helicopters dumped neutron-absorbing materials into the exposed core to prevent it from going critical (meaning that it would have the minimum fissile mass to sustain its own nuclear chain reaction). Sand and other fire-fighting materials were also dropped into the core to help stop the graphite fire. All in all, over 5000 metric tons of material were dropped into the core.
After the fires were brought under control, construction of what is called "the sarcophagus" began. The word "sarcophagus" is usually used to describe the elaborate coffins the ancient Egyptians used to entomb their dead. In this case, the sarcophagus is a structure erected from about 300,000 metric tons of concrete that surrounds the reactor. It was designed to contain the radioactive waste inside. It served its purpose well, but about 10 years after the accident, several flaws were found in it. Holes had begun to appear in the roof, allowing rainwater to accumulate inside. This water could corrode the structure, further weakening it. Also, birds and other animals had been seen making homes in the sarcophagus. If they should ingest radioactive material, they could spread it around the countryside. In short, the sarcophagus had become worn down from normal "wear and tear." It was conceivable that an intense event like an earthquake, tornado, or plane crash directly on the sarcophagus could lead to its collapse. This would be catastrophic, as radioactive dust would once again rain down on the surrounding areas.
Scientists and engineers have been working on ways to repair or replace the sarcophagus. On September 24, 2010, a French contractor called "Novarka" began work building a new sarcophagus. Over the last 3 years since the project was approved, Ukrainian authorities have done clean up of the site and demolished buildings. The 108-meter-high arched structure, weighing 20,000 metric tons, will be assembled close to the reactor and then slid over the existing sarcophagus on rails. The work is being financed by an international foundation.
One of the great tragedies of the accident was that the Soviet government tried to cover it up. Clouds of fallout were traveling towards major population centers (such as Minsk), and no one was warned. No one outside the Soviet Union knew about the accident until two days later, when scientists in Sweden detected a massive amount of radiation being blown from the east.
The effects of the disaster at Chernobyl were very widespread. The World Health Organization (WHO) found that the radiation release from the Chernobyl accident was 200 times that of the Hiroshima and Nagasaki nuclear bombs combined. The fallout was also far reaching. For a time, radiation levels in Scotland were 10,000 times the norm. Thirty lives were directly lost during the accident or within a few months after it. Many of these lives were those of the workers trying to put out the graphite fire and were lost from radiation poisoning. The radiation released has also had long-term effects on the cancer incidence rate of the surrounding population. According to the Ukrainian Radiological Institute, over 2500 deaths resulted from the Chernobyl incident. The WHO has found a significant increase in cancer in the surrounding area. For example, in 1986 (the year of the accident), 2 cases of childhood thyroid cancer occurred in the Gomel administrative district of the Ukraine (the region around the plant). In 1993 there were 42 cases, which is 21 times the rate in 1986. The rate of thyroid cancer was particularly high after the Chernobyl accident, because much of the radiation was emitted in the form iodine-131, which collects in the thyroid gland, especially in young children and pregnant women. Other cancer incidence rates didn't seem to be affected. For example, leukemia was no more prevalent after the accident than before.
What caused the accident? The obvious cause is human operator error. The human operator was not very familiar with the reactor and hadn't been trained enough. Additionally, when the accident occurred, normal safety rules were not being followed, because they were running an experiment. That is, regulations required that at least 15 control rods always remain in the reactor. When the explosion occurred, less than 10 were present. This happened, because many of the rods were removed to raise power output, which was one of the direct causes of the accident. Also, the reactor itself was not designed well and was prone to abrupt and massive power surges.
The End
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