Newport city centre then wheeeyyyyyy

I suspect it’ll probably end up in the same places most other large hazardous industrial sites will be - rural, coastal just off an arterial road route somewhere. See also: Torness, Easington, Milford Haven etc.

That said, Tom Scott did a video (because of course he did) on plans for nuclear testing on UK soil - have a look if you’re interested - and it seems the answer to that was underneath a chunky section of Yorkshire moorland.