The us navy has been building SMRs for decades. Their reactors don't need to generally be refueled either since they use higher grade fuels and burn them in place for 30+ years. So, there are differences but mostly these aren't cutting edge designs, they are 50 year old concepts that have been studied and understood to death.

Yes there are differences, but the fact that the NRC can't certify a reactor class that the navy builds (without interference from the NRC) is itself a problem.