ACCIDENTS
LEVEL 7 - MAJOR ACCIDENT - External release of a large part of the radioactive material in a large facility like a power reactor, threatening serious health effects; delayed health problems over a wide area, possibly involving several countries; long-term environmental consequences.
Example: The 1986 Chernobyl nuclear power plant disaster in the Soviet Union, now in Ukraine, caused widespread environmental and human health problems.
LEVEL 6 - SERIOUS ACCIDENT - Large external release of radioactive material, likely to result in full use of emergency measures to limit serious health problems.
Example: The 1957 accident at the Kyshtym reprocessing plant in the Soviet Union, now Russia, led to a large off-site release. Emergency measures including evacuation of the population were taken.