https://en.wiktionary.org/wiki/experimental

Experimental - Noun "The subject of an experiment"

Posted article indicates that even if the experiment performs to expectations, there will still be waste to be disposed of. They hope to convert most of the nasty, longer-lived radionucleides into something useful, but most is not all. Plus, part of their selling point is conversion into medical radionucleide sources, and to be honest, the market there isn't all that big (like, "a single reactor in Canada supplied a high percentage of these sources for many years" not-that-big). It can probably absorb the output of this reactor, but ramp the idea up into a general solution for all nuclear waste everywhere, and we'll likely end up with more medical and industrial radionucleide sources than we know what to do with.

(There's also the question of what kinds of waste could be reprocessed. Only enriched waste from light-water reactors? What about waste from heavy-water reactors, which tends to be bulkier but considerably less radioactive?)