I think that is a given. The nuke would be simply for getting the caldera to blow.
The ones making the threat were the ones highlighting it as a “radioactive eruption.”
In reality I don’t think any amount of nukes would make the caldera blow. There are already loads of conduits to the surface (geysers, hot springs, pools) so trying to create another with explosives would be useless. A path to the surface is not what is lacking.
It won’t blow until something from below makes the magma chamber swell to an unstable state.
You are off (size of nuke needed) by a couple orders of magnitude.
... Unless she’s ready to blow anyway.