When I was in South Africa their pebble bed reactor was the thing. They were working on it from 1993 until 2009 then gave up. Not totally sure why. https://en.wikipedia.org/wiki/Pebble_Bed_Modular_Reactor

There was a German one too:

>constructed in 1960, grid connected in 1967 and shut down in 1988. It was a 15 MWe, 46 MWt test reactor used to develop and test a variety of fuels and machinery. ... Over its lifetime the reactor had many accidents, earning it the name "Shipwreck".

Not quite sure what goes wrong but they seem problematic.

This is clearly not true because nobody is building one of those? Not just in the West. The one that's actually getting built is PWR.