See

http://us.cnn.com/2007/US/01/29/reac...ity/index.html

I agree with the NRC. Nuclear plants are designed to readily
withstand far worse than the impact of an aircraft, such as internal
steam explosions. Aircraft are light and fragile, and would simply
crumple uselessly if they hit a containment building or cooling tower
(and cooling towers aren't terribly critical). The same is true of
aircraft hitting structures like dams: if the dam can resist a
bazillion tons of water pressing against it 24 hours a day, an
aircraft hitting it would be like a fly against Mount Shasta.

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