There were two or three backup sites within 15 miles of Dinorwig that were being evaluated prior to it being built. There in case the main site proved impractic

There were two or three backup sites within 15 miles of Dinorwig that were being evaluated prior to it being built. There in case the main site proved impractical or too expensive for some reason. I'd posit there are ample disused quarry sites that could serve a similar purpose scattered around the UK, US and much of the developed world.