Light water reactors make relatively inefficient use of nuclear fuel, mostly using only the very rare uranium-235 isotope. Nuclear reprocessing can make this waste reusable, and newer reactors also achieve a more efficient use of the available resources than older ones. With a pure fast reactor fuel cycle with a burn up of all the uranium and actinides (which presently make up the most hazardous substances in nuclear waste), there is an estimated 160,000 years worth of Uranium in total conventional resources and phosphate ore at the price of 60–100 US$/kg.