You might be surprised to discover that a 40 year old life is fairly standard in nuclear power plants[1], in fact some countries hope to keep their plants active for closer to 60 years. At close to $7B+ investment in just the building phase of a modern nuclear plant and close to 7-10 years construction time per plant[2], the limited lifetime of the plant does start to become a concern in the financial sense though.
I'm not balking at the age and saying that the place is 'falling apart.' I'm saying that they were designed 40 years ago, and that it's possible that we've learned things since then and can build better plants (starting at the design phase). I'm no expert though, so I'm making no claims.
[1]: http://www.iaea.org/newscenter/news/2007/npp_extension.html [2]: http://en.wikipedia.org/wiki/European_Pressurized_Reactor