Chernobyl, Ukraine - Nuclear Power Plant Meltdown

Chernobyl, Ukraine

Nuclear Power Plant Meltdown

The accident at the Chernobyl Nuclear Power Plant in Ukrainian produced a plume of radioactive debris that drifted over parts of the western USSR, Eastern Europe, and Scandinavia. The accident, which occurred on April 26, 1986, was the worst nuclear power accident in history. Large areas of the Ukrainian, Belorussian, and Russian republics of the USSR were contaminated, resulting in the evacuation of roughly 200,000 people. The accident raised concerns about the safety of the Soviet nuclear power industry, slowing its expansion for a number of years, while forcing the Soviet government to become less secretive.

The Chernobyl' Nuclear Power Plant was one of the largest in the USSR. It was located just outside of the town of Pripyat', about 18 km northwest of the town of Chernobyl'. The plant was only 16 km from the border between the Ukrainian and Belorussian republics and roughly 110 km north of Kiev, the capital and largest city of Ukraine. Construction of the plant began in the 1970s, with reactor No. 1 commissioned in 1977, followed by No. 2 (1978), No. 3 (1981), and No. 4 (1983). Each reactor had an electricity-generating capacity of 1,000 megawatts, and the four together produced about 10 percent of Ukraine's electricity at the time of the accident. Two more reactors (No. 5 and No. 6, also capable of producing 1,000 megawatts each) were under construction at the time of the accident. On the morning of April 26, 1986, reactor No. 4 was operating at very low capacity (6 to 7 percent) during a planned shutdown. Plant personnel intended to monitor the performance of turbine generators, which supplied electric power for the plant's own operation, during a changeover from standard to a backup source of power. The reactor's design made it unstable at low power, and the operators were careless about safety precautions during the test. After a sudden power surge, two explosions destroyed the reactor core and blasted a large hole in the roof of the reactor building. Radioactive debris moved up through this hole to heights of 1 km.

An estimated 100 to 150 million curies of radiation (primarily radioactive isotopes of iodine and cesium) escaped into the atmosphere before cleanup crews were able to bring the fires under control and stabilize the situation two weeks later. Prevailing winds carried the radioactivity northwest from the plant across Belorussia and into Poland and Sweden, where heightened radiation levels detected on April 28 first brought the accident to the world's attention. Subsequently, from May 1 to 5, wind patterns shifted so that the bulk of radioactivity was carried more directly north and northeast, over Belorussia and southwestern Russia.

After the explosion, firefighters and other workers arrived on the scene in an attempt to contain the blast. To reduce emissions, the team bombarded the reactor with 5,000 metric tons of shielding material consisting of lead, boron, sand, and clay. A second concrete foundation was constructed under the reactor to prevent contamination of groundwater. Finally, workers erected an enormous concrete-and-steel shell over the damaged reactor to prevent radioactive materials, including gases and dust, from escaping.

Soviet officials placed the death toll at 2 (both workers killed during the explosion at the No. 4 reactor) but by mid-August changed the figure to 31, caused from acute radiation exposure during the cleanup. The No. 1 and No. 2 reactors, in fact, were returned to service in November 1986 and the slightly damaged No. 3 unit was restarted in December 1987.

More than 100,000 people were evacuated