Such a device would involve enclosing the reactor, its coolant, the turbine & pump in a single sealed container. Heat pipes could be inserted into blind tubes that enter the interior cavity without compromising the seal. If a heat pipe failed, bit deal. There would be dozens of others.

A properly designed reactor-generator could have a single moving part, the rotor on which the turbine, pump, and generator were all mounted. Even the control rods could be external to the seal, entering blind tubes invaginated from the surface of the sealed vessel.

The best fluid would probably be xenon, which has the right thermal properties to make a small turbine possible. It is utterly non-corrosive. It is also immune to chemical decomposition from the reactor's radiation.

David F Mayer