A multi-billion-dollar mess over partially-built nuclear plants in South Carolina could impact whether Virginia goes forward with a pricy new reactor of its own. Two South Carolina energy companies recently decided to abandon construction of two unfinished nuclear reactors over delays and their high costs, a move that leaves ratepayers there on the hook for billions of dollars with nothing to show for it. The failure in South Carolina to make new nuclear work could make it harder for Virginia’s largest electric utility, Dominion Energy, to move forward with a new reactor it has been considering for years and already spent millions on. The proposed plant, known as North Anna 3, has a sky-high price tag — one state regulator last year calculated it to be about $25 billion — and would significantly increase customer’s electric bills. But Dominion has argued it’s an option worth considering, as nuclear energy provides reliable, carbon-free energy. Sen. Frank Wagner, a leader in energy issues in the state Senate and strong supporter of Dominion, told company officials at a committee hearing Wednesday that South Carolina’s woes concerned him about the viability of North Anna 3.