Lunar Solid State Reactor

After rethinking NASA's lunar reactor design, I came up with an alternative. NASA utilized at least 20% enriched fuel. In my previous space reactor designs, I always opted for depleted Uranium as fuel. Starting with 20% enrichment simplifies many things. Instead of utilizing the heat of the reactor to drive mechanical engines to generate electricity, I opted for thermophotovoltaic electric conversion, which has no moving parts and offers excellent solid-state efficiency.

The enriched Uranium would be placed in a Tungsten shell at the center of the reactor, serving as a nuclear light bulb. The immense heat of the fission will make the Tungsten shell glow, emitting near-infrared photons that are converted into electricity by advanced GaInAs (Gallium Indium Arsenide) solar cells surrounding the central core. There will be a vacuum void separating the cells from the core to eliminate conductive and convective thermal coupling. The solar arrays will be cooled by heavy water (D₂O) from their backside. The heated heavy water will evaporate and rise up to the condensation chamber where it will condense via Aluminum heat exchangers and drop back as liquid into the cooling reservoir. As a result, there will be no mechanical pumps used for cooling.

Heavy water will have a second purpose in the system: it will act as the moderator. Because heavy water has a near-zero neutron absorption rate, it will efficiently moderate the fast neutron flux emitted by the glowing core and reflect them back without absorbing them. This will keep the core's neutron economy above the critical point to self-sustain fission. The heavy water will be initially stored in an insulated compartment below the reactor during transportation from Earth to the Moon. Once the reactor's system checks give a "Go" signal, it will be introduced into the cooling section behind the solar cells, establishing the moderator link to initiate fission.

The system is entirely self-stabilizing. If the fission in the core increases, the increased radiant heat will instantly vaporize more heavy water molecules behind the solar cells, reducing the local liquid moderator density. This negative void coefficient will naturally slow the fission rate and self-stabilize the system. The fission reaction can be shut off just as easily by draining the heavy water back into its reservoir at the bottom.

Finally, a truly solid-state nuclear reactor with a compact footprint and exceptional weight savings can be achieved with this design. Because the system contains no high-frequency mechanical engines, it eliminates the destructive structural vibrations that plague dynamic reactors. This makes it an ideal, plug-and-play power block for highly sensitive scientific landers and heavy autonomous rovers, as it will not interfere with high-precision sensors or scientific instrumentation. Furthermore, because the core remains deeply subcritical and completely inert during transit, it offers an unprecedented safety profile for launch from Earth—only waking up once safely positioned on the lunar surface and given the "Go" signal to initialize the fluid loop.