Pb-Te thermoelectrics can achieve an efficiency of 20% with Thot = 875K and Tcold=300K. Thermal neutron fission cross sections are have a strong negative relationship to temperature. Graphite, silicon carbide, and beryllium all remain great thermal conductors and neutron moderators after irradiation at 875-1000K. Based on this it should be possible to make a fission power plant with no moving parts whatsoever. Thereby the entire plant would meet all four of the IAEA's criteria for passive safety: https://en.wikipedia.org/wiki/Passive_nuclear_safety. Resolves YES if such a plant exists before 2050. Minimum 1KWe (so micro-reactors on space probes count).