When environmentalists arrived at the site of a future nuclear weapons factory in South Carolina, they found a massive building being gutted so that it can one day house production lines for plutonium pits, some of the most important elements of atomic bombs.

Parts of the building’s interior had been ripped out, holes had been knocked in walls, and wiring and pipes had been removed, factory critic Tom Clements said Wednesday, a day after he toured the future plutonium pit plant.