The transformation of radioactive uranium and, in some instances, thorium isotopes provides vastly more energy per unit mass of fuel than any other energy source, except nuclear fusion, and therein lies its greatest attraction. The unit considers the advantages and limitations of generating this power and the environmental and security issues that the process raises. This study unit is just one of many that can be found on LearningSpace, part of OpenLearn, a collection of open educational resources from The Open University. Published in ePub 2.0.1 format, some feature such as audio, video and linked PDF are not supported by all ePub readers.