Innovative High Temperature Heat Pipes for Spacecraft Nuclear Fission Systems

NASA Glenn is examining small fission reactors for future space transportation and surface power applications. The reactors would have an 8 to 15 year design life that could be available for a 2020 launch to support future NASA science missions. Both 1 kWe thermoelectric and 3 kWe Stirling systems have been examined. The proposed design will use alkali metal heat pipes to transfer heat from the reactor to the Stirling or Thermoelectrics (TEs) convertors. This SBIR project by ACT will develop alkali metal heat pipes for space nuclear fission reactors. Three types of alkali metal heat pipes will be investigated over the course of the 6 month Phase I program; arterial heat pipes, grooved heat pipes and self-venting arterial heat pipes that use a screen wick artery with vent holes. Grooved and self-venting heat pipes will be fabricated and tested to determine which design would be best suited for the space fission reactor application.

The immediate NASA application is for space fission nuclear reactors that utilize Stirling converters or thermoelectric for power conversion. An example is the 1kWe Fission Power System with a 15 year design life that could be available for a 2020 launch. The reliable, low-mass, alkali-metal heat pipes developed in this program would be capable of transporting the reactor heat to the Stirling or thermoelectric convertors for power generation. The Stirling system and other space nuclear reactors also require radiator panels to reject waste heat. The grooved and self-venting arterial heat pipes developed on this program will also be suitable to the lower temperature radiator heat pipes.

There is a commercial application for high temperature VCHP heat exchangers in fuel cell reformers. In a fuel cell reformer, steam, air and diesel fuel react in a High Temperature Shift (HTS) and a Low Temperature Shift (LTS) reactor to produce as much hydrogen as possible. Feed streams to and from the reactors must be maintained under tight temperature control, typically within ¿30¿C despite a turndown ratio of 5:1 in reactant flow rate. Isothermal Furnace Liners (IFLs) use an alkali metal heat pipe to provide nearly isothermal temperature uniformity over the entire length and circumference of the tube furnace wall. A Pressure Controlled Heat Pipe (PCHP) can provide extremely precise temperature control. ACT will use the results of the current program to extend the PCHP technology to high temperature IFLs. These PCHPs can be used by organizations such as national labs to aid in thermophysical properties characterization and temperature calibration of primary temperature reference standards.

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