There are some experimental IV generation Fission Reactors, which burn the entirety of the nuclear fuel leaving just lighter radioactive elements with shorter h

There are some experimental IV generation Fission Reactors, which burn the entirety of the nuclear fuel leaving just lighter radioactive elements with shorter half-life. Regarding safety, the Molten-salt Reactor also of IV generation, allows for non catastrophic failures since if the reaction goes out of control, the salt solidifies and stops the reaction instead of exploding by the increased pressure. The downside is that reactor becomes a radioactive rock.