Research never stopped. Problem is US Government refused to look. So meanwhile Westinghouse is building state of the art nuclear power plants in China.
Something the NRC would never have accepted: Unified Single Design. Every single US nuclear power plant is a one-off custom. Westinghouse built a factory in China which builds huge blocks of buildings which are shipped to site. Every one is identical. The pipes are routed the same way in every plant. State of the art reactor.
When WWII started the Navy used to build every ship custom and unique. Had to figure the same things out, again, for every ship. Slow production until finally decreed every ship shall be built to the same blueprint. Then when an issue developed with one ship they knew to look for same in all the others.
Westinghouse could start building the same in the USA tomorrow but for the need for the NRC to maintain its empire by reviewing, re-reviewing, arbitrarily revising, reviewing again, holding hearings, review some more, adjust the permits and design in the midst of construction for 15 years.