Don’t recognize THTR ... Thermal Thorium Reactor?
There was a german project with a pebble bed reactor that actually delivered some power to the grid but was cut off power and sealed because of ‘economical troubles’ - they had some trouble with the pebbles falling apart and could'not find a company to post-process the burned off pebbles.
The concept is pure genius - because it’s a very straight forward construction and uses an abundant source.
I think the South Africans are following that idea and the US had (or have) an approach with a brick shaped fuel element reactor.