CHERNOBYL

WHEN AND WHAT

• Seven years after the incident at Three Mile Island, on April 25, 1986, a crew of engineers with little background in reactor physics began an experiment at the Chernobyl nuclear station. They sought to determine how long the plant's turbines' inertia could provide power if the main electrical supply to the station was cut. Operators chose to deactivate automatic shutdown mechanisms to carry out their experiment

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• The four Chernobyl reactors were known to become unstable at low power settings,and the engineers' experiment caused the reactors to become exactly that

WHAT HAPPENED

• The episode was exacerbated by a second design flaw: The Chernobyl reactors lacked fully enclosed containment buildings, a basic safety installation for commercial reactors in the U.S.

THE OUTCOME

• Chernobyl was the result of human error and poor design. Of the approximately 50 fatalities, most were rescue workers who entered contaminated areas without being informed of the danger.

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• The World Heath Organization says that up to 4,000 fatalities could ultimately result from Chernobyl-related cancers. Though these could still emerge, as yet, they have not. The primary health effect was a spike in thyroid cancer among children, with 4,000-5,000 children diagnosed with the cancer between 1992 and 2002. Of these, 15 children unfortunately died.

TECHNOLOGY IMPROVEMENTS AND LESSON LEARNED

• Comparing the technology of the nuclear reactor at Chernobyl to U.S. reactors is not fair. First, the graphite-moderated, water-cooled reactor at Chernobyl maintained a high positive void coefficient.

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• Given the inherent problems with the Chernobyl reactor design, many technological changes and safety regulations were put in place to prevent another Chernobyl-like meltdown from occurring. Designers renovated the reactor to make it more stable at lower power, have the automatic shutdown operations activate quicker, and have automated and other safety mechanisms installed.[16]