Hot End Thermal Management System for Nuclear Electric Propulsion

Nuclear electric propulsion systems provide a variety of benefits including increased science payload, reduced flight times and longer mission lifetimes. These advantages enable a wide range of missions such as manned missions to Mars, unmanned missions to the outer planets and deep-space. The thermal management system linking the reactor to the hot end of the power conversion system must be efficient, lightweight and reliable. These requirements become more challenging as the total power scales to the megawatt level. The Phase I program included successful demonstration of high-power heat pipes and the development of a reactor design. In this Phase II SBIR program, Advanced Cooling Technologies will lead the development and maturation of a highly reliable, efficient, and lightweight heat pipe-based thermal management system for the hot end of the power generation system for nuclear electric propulsion. High-power heat pipes will be used be used to transport thermal energy, at the megawatt scale, to the hot end of the power conversion unit. The proposed system is passive and highly reliable with built-in redundancy. Nuclear electric propulsion systems allow for increased science payload, reduced flight times and longer mission lifetimes. The thermal management system linking the reactor to the hot end of the power conversion system must be efficient, lightweight and reliable while operating at the MW scale. The Phase I program demonstrated high-power heat pipes carrying 3kW over a meter, a full-scale 10MW reactor design, and a heat pipe based thermal management system capable of high heat flux (>0.3MW/m2) and minimal temperature drop (<50K).   In this SBIR program, Advanced Cooling Technologies in collaboration with USNC-Tech will develop a reliable, efficient and lightweight thermal management system for the hot end of the power generation system for nuclear electric propulsion. High-power alkali metal heat pipes will passively transport thermal energy from the nuclear reactor to a bank of modular heat exchangers. The heat exchangers extract thermal energy for the power conversion system. The heat pipe based thermal management system is fully passive and reliable with built-in redundancy. The overall technical objective of the SBIR program is to develop a reliable, lightweight thermal management system for the hot end of a nuclear electric propulsion system. In the Phase I program, small-scale high-power heat pipe prototypes were successfully demonstrated and a full-scale heat pipe based nuclear electric propulsion system was designed. The goal of the Phase II program is to significantly scale up the size and power of the heat pipes and to optimize the design of the thermal management system.   In the Phase II, ACT will advanced the ability to fabricate long annular wicks for high power heat pipes, demonstrate improved small-scale high-power thermal performance with improved wicks, and build one small-scale refractory metal high-power heat pipe. This will be followed by analyzing and optimizing the design of the primary heat exchanger and the startup loop heat exchanger used for enabling the startup of long alkali metal heat pipes. A small-scale prototype of heat pipes and the primary heat exchanger will be developed. The interface between heat pipes and the reactor core will be studied theoretically and experimentally. Finally, ACT will design, fabricate, and demonstrate a 5m long high-power sodium heat pipe.

The thermal management technology proposed here is relevant to several areas of NASA’s Technology Roadmap, including “Power for In-Space Propulsion”, “Fission Space Power and Energy Storage” and “Heat Transport for Thermal Control Systems”. The system will benefit many space-based fission power systems such as nuclear electric propulsion and power generation on the lunar and Martian surface. The proposed system is capable of transporting a significant amount of thermal energy from a nuclear reactor to a power conversion system. In addition to space-based applications, the thermal management system is relevant to small modular and micro nuclear reactors. Small reactors have several advantages including reduced capital investment, reduced construction time and scalability.

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