The process for licensing a LWR is well established. Commercial LMFBR (Fermi 1) and HTGR (Peach Bottom 1) reactors have been approved in the US but those were a very long time ago. Anybody who wants to license a new reactor type is going to work through an extensive process with the NRC to determine how exactly it is done.

They built an MSR in Wuwei, China and just got approval to start it.

https://www.world-nuclear-news.org/Articles/Chinese-molten-s...