2005 - Space Nuclear Power - Reactor Coolant & Power Conversion

This Naval Reactors letter NR:RE:KHDonald I#05-01228 dated April 20, 2005 details the approval of a reactor coolant and power conversion system for Project Prometheus, a space nuclear power initiative for NASA.

Selected Concept

NR approved the selection of a gas-cooled reactor with a directly coupled Brayton cycle engine for further development. The Naval Reactors Prime Contractor Team (NRPCT) identified this configuration as providing the optimal balance of performance, scalability, testability, and deliverability.

Letter Identifies the Key Advantages of the Gas-Brayton System:

Simplicity: It is the least complex concept with the fewest components to engineer.

Safety and Maintenance: Inert gas is easier to handle than reactive liquid metal coolants, reducing life-limiting corrosion risks.

Operational Benefits: The system uses single-phase coolant, eliminating the need for remote thawing in space, and allows for a wider selection of materials to potentially reduce reliance on refractory metals.

Testing: Lower component temperatures may facilitate ground-based testing and mission extendibility.

Dissenting View and NR Conclusion

A minority within the NRPCT favored a heat pipe-cooled reactor, arguing it would provide greater redundancy through multiple, independent loops. However, the majority and NR expressed concerns regarding the potential for common-mode failures in heat pipes, noting that their performance and failure mechanisms remain insufficiently characterized. Furthermore, the complexity of developing heat pipe technology was deemed likely to exceed NASA's project schedule.