The article itself does not describe how it is done. Most likely a publicity stunt to accept the notion “nuclear waste is not a problem, it will be eliminated eventually”.
Oh, and they need sustainable fusion, a thing unobtainable for another hundred or thousand years. That we might do sustainable fusion in five years does not count, firstly they don’t know anything about it, and secondly fission reactors would be outdated then anyway.
That they can do it in a laboratory does not mean it is economically feasible: total energy input is quite probably higher than the combination of fission reactor output and waste elimination plant energy input.
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