As in any big government-connected project in the US, today, whether it involves tunnels (Big Dig, 2nd Ave subway, Yucca Mountain), military procurement (F-35, literally dozens of others), manned spaceflight (STS, ISS, SLS) or construction projects, notably nuke plants and "high-speed rail", and even fusion "research", waste and cost overruns are not problems.
Rather, they are the whole point of the projects. They provide a steady, voluminous, years-long, indictment-proof flow of public money to select private pockets under control of select politicians. Initial cost estimates are always entirely fictional, with no intention ever to deliver anything at the promised price.
This is a reason why "small modular nuke" has never gained traction in the US: there is just not enough scope for massive wholly-legal corruption.
It has taken many decades, but the US has achieved world domination in high-level legalized corruption. It is largely impossible for honest, legitimate projects to compete for backers, except, lately, solar and wind power farms, which can be built very quickly and start delivering power before they are even finished.