You don't need much enriched uranium, but you need to process a lot of dirt to get it. Natural uranium concentrations are around 0.1-0.2% (copper is around 0.6%

You don't need much enriched uranium, but you need to process a lot of dirt to get it. Natural uranium concentrations are around 0.1-0.2% (copper is around 0.6%), and you need 10 tonnes of natural uranium to produce 1 tonne of enriched uranium. Furthermore, unlike copper, steel and other metals, uranium can't currently be recycled. See my previous post