Physicist Reviews Nuclear Meltdowns - nytimes

Excerpt:
"Given that in the history of nuclear energy, 582 reactors have operated for a total of 14,400 years (counting each year of operation by one reactor as a reactor-year), a core-damage accident has happened once every 1,309 years of operation. With 439 reactors now operating worldwide, the rate would yield an accident an average of once every three calendar years."

Complete article:
http://www.nytimes.com/2011/04/12/science/12nuclear.html?_r=1