Do nuclear reactors use uranium 235 or 238?

The isotope U-235 is important because under certain conditions it can readily be split, yielding a lot of energy. It is therefore said to be 'fissile' and we use the expression 'nuclear fission'. Meanwhile, like all radioactive isotopes, they decay. read more

Uranium from the ground is over 99% uranium 238. But a small amount is also uranium 233, 234, 235, 236, 237. What they need to do is then ENRICH it. Meaning they take out more and more 238 so a greater and greater percentage of what’s left is 235. Weapons grade isotope is 50–90% 235. read more

When the uranium fuel has been in the reactor for about three years, the used fuel is removed, stored, and then either reprocessed or disposed of underground (see Nuclear Fuel Cycle or Radioactive Waste Management in this series). read more