Theoretically, it is possible to transmute all the isotopes produced by fission reactions into stable elements, and do so with a large net power gain.

In practice, it needs specialized reactors, and the ability to chemically process and separate out highly-radioactive isotopes so they can be exposed in those reactors. It has been demonstrated on a small scale many times. France has and Japan at least have experimented with reusing waste by transmuting it into new useful fissile material.

It's an interesting question of whether it could scale to the entire nuclear power fuel cycle. Canada's total nuclear waste output is measured in hundreds to perhaps a thousand tonnes a year, and almost all of it, numerically, could be separated out and processed into useful nuclear fuel.

A near closed-loop requiring perhaps a few tonnes of raw uranium a year is the theoretical ideal. It's technically possible, but I have no idea if it's affordable to do.