What you actually need is mass production, and a regulatory environment that facilitates the same, e.g. by putting most of the certification in the design phase and then making production certification limited to the matter of whether what was built follows the certified spec.
The ideal would be to limit the on-site construction to common fungible commodities like pouring concrete and have any reactor-specific components mass produced in a factory. Then the same factory can be producing components for reactors whether they're going up in New York or Seattle or London and you get your economies of scale.