Modern SMRs (small nuclear reactors) can literally use spent fuel rods from legacy nuclear reactors as their primary fuel. This isn’t conjecture but simple fact. The engineering has dramatically improved even if public sentiment hasn’t. Modern nuclear reactors can not melt down in same way the reactor at Chernobyl did.

The new “fast reactors” are explicitly designed to take spent fuel rods as fuel to lessen the requirement of creating more enriched uranium.