It just makes them larger. And it makes the building containing them larger. And this makes them more expensive. NuScale's reactor was originally motivated by

It just makes them larger. And it makes the building containing them larger. And this makes them more expensive. NuScale's reactor was originally motivated by the desire to make it safer by using natural convection. But it ends up requiring 1/3rd more labor hours to build a NPP using their reactors than it does to build a conventional large reactor power plant.