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At 1:23 a.m. on April 26, 1986, the worst nuclear-power accident in history occurred at Chernobyl, Ukraine, which was then part of the Soviet Union. Twenty years after the accident, the name “Chernobyl” and a view of the 90-meter-high concrete and steel sarcophagus covering Reactor Four at the power plant serve as a potent reminder of the devastation nuclear energy can wreak upon humanity whether in the form of weapons or power generation.

The Chernobyl inferno also had a political effect. It taught the Soviet leadership that it could not run a country in a secretive manner in the nuclear age. As former Soviet leader Mikhail Gorbachev admits, the Chernobyl disaster opened the possibility of much greater freedom of expression to the point that the Soviet system could no longer survive, thus making the Chernobyl accident perhaps one of the primary causes of the Soviet Union’s collapse.

The accident occurred while a special test was being carried out at the 1 million-kW reactor. The reactor’s output was decreased to a low level to see how long turbines would spin and supply power following a loss of the main electrical power supply. Due to operational errors and a disregard for safety procedures, the chain reaction in the reactor went out of control.

Two explosions blew off the reactor’s heavy steel and concrete lid. Radioactive material 500 times greater than that released by the atomic bomb dropped on Hiroshima poured into the atmosphere. Although people in Ukraine, Belarus and Russia suffered the most from contamination, radioactive material was detected in many other parts of the Northern Hemisphere — as far away as Japan. Some 116,000 people living within a radius of 30 km from Chernobyl were evacuated. The number of evacuees eventually reached 350,000. Some 500 towns and villages became ghost towns.

Clean-up workers as well as evacuees and residents have since suffered from cancer and leukemia. About 200 tons of high-level radioactive materials remain in the core of the sarcophagus-covered Reactor Four.

Estimates of the death toll from the disaster vary. In a September 2005 report, the United Nations Chernobyl Forum, a consortium of eight U.N. agencies — including the International Atomic Energy Agency — plus Russia, Ukraine and Belarus, stated that 47 deaths between 1986-2004 were directly linked to radiation exposure and that a total of 4,000 of the 600,000 people mobilized for the cleanup operations have died or are likely to die from radiation-related cancers and leukemia. It also stated that there was no convincing evidence of birth defects or reduced fertility. Ecological groups accuse the consortium of underestimating the health damage.

The World Health Organization in a recent report estimated Chernobyl-related cancer deaths at 9,000 among clean-up workers, evacuees and residents in the contaminated areas. It also stated that about 5,000 people who were children at the time of the accident are now suffering from thyroid cancer and that more cases will arise. These reports, however, are based on estimated amounts of radiation and the number of people exposed to radiation. Only thorough epidemiological studies spanning a long period of time will produce convincing results.

A design flaw in the RMBK-type reactor used in Chernobyl was largely responsible for the disaster. Although Japan does not use this kind of reactor, its nuclear-power industry cannot be too cautious in operating the reactors that now supply about 30 percent of the nation’s electricity.

In an RMBK type reactor, graphite is used as “moderator” and boiling water serves as coolant. (Moderator reduces the speed of fast neutrons — a process necessary to increase fission.) If water coolant is lost or turned into steam, absorption of neutrons by the coolant will decrease and a chain reaction will accelerate. This effect led to the power surge and eventual explosions at Chernobyl.

In pressurized or boiling light-water reactors, as used in Japan, water serves as both moderator and coolant. If the temperature in the reactor core goes up and the steam void increases, the amount of coolant decreases. A decrease in the amount of coolant also means a decrease in the amount of moderator, which automatically leads to a deceleration of the chain reaction. This design strength, however, should not give plant operators a false sense of security.

Originally developed as weapons, nuclear power is inherently dangerous. Even when utilizing nuclear power for peaceful purposes, utmost care is indispensable. Anyone familiar with the Chernobyl accident would do well to imagine the dreadful effect of nuclear weapons and consider the need to abolish them.

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