First Fuel Produced for the Idaho National Lab's Experimental Molten Salt Reactor.

[NNadir]

4. The Pressurized Water Reactor is the most successful and safest energy device ever placed in commercial use...

...on a large scale.

The best existing device for burning used fuel is the CANDU, particularly alloyed with thorium, since it can function as a breeder, albeit with a much longer doubling time than a fast reactor.

This said, all of the reactor designs I discuss with my son are designed to burn used fuel, in particular, reactor grade plutonium (or, for that matter, weapons grade with the goal of denaturing it.)

Once through uranium has properties that make it superior to natural uranium, in particular an isotopic vector including ²³⁶U, not found in natural uranium.

The biggest drawback to the PWR is that it is only useful for generating electricity. (In rare cases, waste heat has been used for district heating.) Other reactors can expand the function well beyond that.