The MC had a military background and saw the coming event. He built an underground bunker connected to a cave system. His neighbors begged him to save and protect their daughters. He had some sort of nuclear generator for power.
I can't remember who the author was. And the story may have been taken down for a re write by the author.
Does this ring any bells with anyone?
'Aftermath' by Greven https://storiesonline.net/library/storyInfo.php?id=39178
Regards G_R
It also sounds like my own three-novel "Great Death" series, though in that one, the protagonist simply builds a home in an existing mountainous cavern, with no reinforced bunker. Thus he has a natural water-based power system, and no massive generators, as I thought it a more 'natural' setting for a completely unnatural story setting.