ONLY ONE BIG PROBLEM... They will still be HIGH PRESSURE VESSEL REACTORS, not MSR or IMSR which operate at 1 - 1.5 bar!
IMSR and MSR reactors can’t “melt down” the fuel is in the the liquid salt mix. If the salt mix gets too hot it looses reactivity and the reaction slows down then cools down then heats up again... They are SELF REGULATING which a high pressure reactors ARE NOT!
You’re conveniently ignoring the problem with MSR reactors - if you ever have to shut them down, you throw the whole thing away.