Can we use waste nuclear heat to generate electricity?

We put this question to Dr Ian Farnan from the Department of Earth Sciences at Cambridge University:

It's a nice idea in principle. I think one of the problems with this boiling water reactor design that's used in Japan is the fact that they use the water that's directly passing over the fuel rods to go straight into the generator. Generators have become very contaminated now. You'd have a similar problem, I think if you started to take the heat out of the spent fuel. I think there's probably not enough heat there to do a double or a primary or secondary type heat exchange, it would then become inefficient and not worth the trouble.