Full-scale nuclear test

The nuclear demonstration test will occur in late summer or early fall of 2017. The test will be conducted at the Device Assembly Facility at the Nevada National Security Site (NNSS). It will be comprised of a ~32 kilogram enriched uranium reactor core (about the size of a circular oatmeal box) made from uranium metal going critical, and generating heat that will be transported by sodium heat pipes to Stirling engines that will produce electricity.

The test will include connecting heat pipes and Stirling engines enclosed in a vacuum chamber siting on the top of a critical experiment stand.The critical experiment stand has a lower plate than can be raised and lowered. On this plate will be stacked rings of Beryllium Oxide (BeO) that form the neutron reflector in the reactor concept. A critical mass is achieved by raising the BeO reflector to generate fission in the reactor core. Once fission has begun, the BeO reflector will be slowly raised to increase the temperature in the system to 800 degrees Centigrade. The heat pipes will deliver heat from the core to the Stirling engines and allow the system to make ~250 watts of electricity. For the purpose of testing only, two of the eight Stirling engines will make electricity,the others will only discard heat.

The data gained will inform the engineers regarding startup and shutdown of the reactor, how the reactor performs at steady state, how the reactor load follows when Stirling engines are turned on and off and how the system behaves when all cooling is removed. This data will be essential to moving forward with a final design concept.

Potential for missions to Mars

Once the nuclear demonstration testing has been completed, the path to putting a nuclear reactor on a NASA mission to deep space or the Mars surface is still several years away. A finalized design must be completed along with rigorous testing of the system for reliability and safety.

The most recent NASA studies have focused on the use of KiloPower for potential Mars human exploration. NASA has examined the need for power on Mars and determined that approximately 40 kilowatts would be needed. Five 10-kilowatt KiloPower reactors (four main reactors plus one spare) could solve this power requirement.

The 40 kilowatts would initially be used to make oxygen and possibly propellant needed by the Mars Ascent Vehicle to send astronauts back into Martian orbit. After making oxygen or fuel, the power would then be available to run the Martian habitat or provided power to Martian rovers all needed by the astronauts during their stay on Mars. Nuclear power has the advantage of being able to run full time day or night, as well as being able to operate closer to the Martian poles where it is believed water exists in substantial quantities.

Lessons learned

Lessons learned from the kiloPower development program are being leveraged to develop a Mega Watt class of reactors termed MegaPower reactors. These concepts all contain intrinsic safety features similar to those in kiloPower, including reactor self-regulation, low reactor core power density and the use of heat pipes for reactor core heat removal. The use of these higher power reactors is for terrestrial applications, such as power in remote locations, or to power larger human planetary colonies. The MegaPower reactor concept produces approximately two megawatts of electric power. The reactor would be attached to an open air Brayton cycle power conversion system. A Brayton power cycle uses air as the working fluid and as the means of ultimate heat removal.

MegaPower design and development process will rely on advanced manufacturing technology to fabricate the reactor core, reactor fuels and other structural elements. Research has also devised methods for fabricating and characterizing high temperature moderators that could enhance fuel utilization and thus reduce fuel enrichment levels.

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Nuclear Reactors to Power Space Exploration - R & D Magazine