CANDU 9

very interesting. for those who want to know how it works:

Most commercial reactor designs use normal water as the moderator. Water absorbs some of the neutrons, enough that it is not possible to keep the reaction going in natural uranium. CANDU replaces this “light” water with heavy water. Heavy water’s extra neutron decreases its ability to absorb excess neutrons, resulting in a better neutron economy. This allows CANDU to run on unenriched natural uranium, or uranium mixed with a wide variety of other materials such as plutonium and thorium. This was a major goal of the CANDU design; by operating on natural uranium the cost of enrichment is removed. This also presents an advantage in nuclear proliferation terms, as there is no need for enrichment facilities, which might also be used for weapons.

From Wikipedia. So the key is to improve the neutron economy sothat there’s more neutrons available; then, these extra neutrons can go on to split extra material, which is thereby consumed.