Earlier quoted context omitted.
The big question is how on earth are they digging out these caverns? That seems like a huge challenge, given that they're so far underground. Everything else seems relatively straightforward
It says repurposing old mining operations. Not sure how feasible that is.
Why was this not built before? I have no idea. Maybe robots are essential, we didn't have deep enough mines that were abandoned, energy was cheaper, no push for no emissions, it's not economical, other risks.