BACKGROUNDChernobyl is located in Ukraine, approximately 110 kilometers north of kyiv, near the Belarusian border. It is a small town of around 12,500 inhabitants. There was a nuclear power plant with four reactors that was built and located about 15 kilometers to the northwest. A 22 km² artificial water reservoir was created to cool the reactor. This power plant used Soviet-designed RBMK-1000 nuclear reactors, considered to be old and outdated designs. This RBMK reactor uses U-235 fuel to heat water, creating steam that turns turbines and produces electricity. Graphite is used to control the reactivity of the core and also to maintain the continuous nuclear reaction that occurs in the core. When the core produces more steam and bubbles, it becomes more reactive and creates a positive feedback loop called the positive vacuum coefficient. Compared to other nuclear reactor designs, water is used as a coolant and to moderate the reactivity of the nuclear core. As the core heats up and produces more steam, increased steam bubbles or voids in the water reduce the reactivity of the nuclear core. This is an important safety feature found in most reactors built in the United States and other Western countries. HISTORY On April 26, 1986, an accident at the Chernobyl nuclear power plant occurred. produced in Chernobyl. The Chernobyl disaster was a catastrophic nuclear accident that caused several explosions and fires. This causes large quantities of radioactive particles to be released into the atmosphere and then spread to the nearby area. The Chernobyl disaster is considered the worst nuclear power plant accident in history. It is classified as a level event on Internati...... middle of paper ...... Ernobyl power station. The highest radiation doses were received by the firefighter and power plant personnel on the night of the accident. Around 600,000 people working in recovery operations (civilian and military) received special certificates confirming their status as liquidators. The evacuation of local residents was carried out at different times after the accident depending on the radiological situation and the distance from populated areas of the damaged reactor. Residents of contaminated areas of the former Soviet Union continued to live in the contaminated territories surrounding the Chernobyl reactor even though efforts were made to limit their doses. The average doses of 134Cs and 137Cs received during the first 10 years after the accident by residents of contaminated areas are estimated at 10 mSv..