A lot of these stations were built at a time when it was felt nuclear power using fission would provide abundant and cheap energy eventually. The current thinking on one side is that they are the only alternative to fossil fuels. This is not necessarily true - we have to move towards sustainable power in the next few decades as both fossil fuels and the nuclear fuel are not sustainable - that is they will run out. At the current world use with the current world known resources according to the nuclear industry we have about 80 years of uranium. This worries potential builders of nuclear power stations who can see they might not get a full return on their investment if the nuclear fuel (uranium) should become hard to get.