My planet is tidally locked, airless, and has no magnetosphere. It's located close to a flare star (5% solar mass, 11 Gyr old), and is in it's habitable zone. The strongest flare ever detected on Earth was class X-100,000, but we've got a very limited time looking at them so be safe so to not underestimate. This flare star is very strong, and very active with mega flares up to class X-10,000,000.
The planetary empire is 25 billion strong and 500 million years old. They live deep underground to protect themselves from the flares. But all the nuclear fuel on the planet is almost spent. I was thinking huge amounts of solar thermal collecting stations are the best way to get energy because the sun always stays overhead - but can infrastructure above ground like vehicles, outposts, computers, and comms. be hardened to survive against these regular mega flares?
Only existing technology please, no handwavium.