Details on relative risk to the nation's 104 nuclear power

(AP) - Chances are remote that a blackout at a U.S. nuclear power plant could lead to the sort of crisis facing Japan. But an Associated Press investigation finds that some nuclear plants are more susceptible to dangers from a power failure than others.

U.S. regulators have long known that a power failure lasting days could lead to a radioactive leak. Yet they have only required nuclear reactor operators to develop plans for dealing with much shorter blackouts - those lasting four or eight hours, depending on the risk.

Regulators say they are confident that measures in place will prevent or significantly delay a reactor's core from melting and threatening a radioactive release. Still, events in Japan are raising questions about whether U.S. power plants are as prepared as they should be.

Following a 30-year period in which few new reactors were built, it is expected that 4-6 new units may come on line by 2018, the first of those resulting from 16 license applications to build 24 new nuclear reactors made since mid-2007.

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(Copyright 2011 by The Associated Press. All Rights Reserved.)