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Comparison of Direct and Indirect Gas Reactor Brayton Systems for Nuclear Electric Space Propulsion.

DE2005850545

Publication Date	2005
Personal Author	Postlethwait, M.; DiLorenzo, P.; Belanger, S.; Ashcroft, J.
Page Count	16
Abstract	Gas reactor systems are being considered as candidates for use in generating power for the Prometheus-1 spacecraft, along with other NASA missions as part of the Prometheus program. Gas reactors offer a benign coolant, which increases core and structural materials options. However, the gas coolant has inferior thermal transport properties, relative to other coolant candidates such as liquid metals. This leads to concerns for providing effective heat transfer and for minimizing pressure drop within the reactor core. In direct gas Brayton systems, i.e. those with one or more Brayton turbines in the reactor cooling loop, the ability to provide effective core cooling and low pressure drop is further constrained by the need for a low pressure, high molecular weight gas, typically a mixture of helium and xenon. Use of separate primary and secondary gas loops, one for the reactor and one or more for the Brayton system(s) separated by heat exchanger(s), allows for independent optimization of the pressure and gas composition of each loop. The reactor loop can use higher pressure pure helium, which provides improved heat transfer and heat transport properties, while the Brayton loop can utilize lower pressure He-Xe. However, this approach requires a separate primary gas circulator and also requires gas to gas heat exchangers. This paper focuses on the trade-offs between the direct gas reactor Brayton system and the indirect gas Brayton system. It discusses heat exchanger arrangement and materials options and projects heat exchanger mass based on heat transfer area and structural design needs. Analysis indicates that these heat exchangers add considerable mass, but result in reactor cooling and system resiliency improvements.
Keywords	Brayton cycle power systems Nuclear electric power generation Space propulsion reactors Spacecraft power supplies Power generation Comparative evaluation Heat exchangers Heat transfer Structural analysis
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Lockheed Martin Corp., Bethesda, MD.; Department of Energy, Washington, DC.
Supplemental Notes	Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200608

Comparison of Direct and Indirect Gas Reactor Brayton Systems for Nuclear Electric Space Propulsion.

Comparison of Direct and Indirect Gas Reactor Brayton Systems for Nuclear Electric Space Propulsion.
DE2005850545

Publication Date	2005
Personal Author	Postlethwait, M.; DiLorenzo, P.; Belanger, S.; Ashcroft, J.
Page Count	16
Abstract	Gas reactor systems are being considered as candidates for use in generating power for the Prometheus-1 spacecraft, along with other NASA missions as part of the Prometheus program. Gas reactors offer a benign coolant, which increases core and structural materials options. However, the gas coolant has inferior thermal transport properties, relative to other coolant candidates such as liquid metals. This leads to concerns for providing effective heat transfer and for minimizing pressure drop within the reactor core. In direct gas Brayton systems, i.e. those with one or more Brayton turbines in the reactor cooling loop, the ability to provide effective core cooling and low pressure drop is further constrained by the need for a low pressure, high molecular weight gas, typically a mixture of helium and xenon. Use of separate primary and secondary gas loops, one for the reactor and one or more for the Brayton system(s) separated by heat exchanger(s), allows for independent optimization of the pressure and gas composition of each loop. The reactor loop can use higher pressure pure helium, which provides improved heat transfer and heat transport properties, while the Brayton loop can utilize lower pressure He-Xe. However, this approach requires a separate primary gas circulator and also requires gas to gas heat exchangers. This paper focuses on the trade-offs between the direct gas reactor Brayton system and the indirect gas Brayton system. It discusses heat exchanger arrangement and materials options and projects heat exchanger mass based on heat transfer area and structural design needs. Analysis indicates that these heat exchangers add considerable mass, but result in reactor cooling and system resiliency improvements.
Keywords	Brayton cycle power systems Nuclear electric power generation Space propulsion reactors Spacecraft power supplies Power generation Comparative evaluation Heat exchangers Heat transfer Structural analysis
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Lockheed Martin Corp., Bethesda, MD.; Department of Energy, Washington, DC.
Supplemental Notes	Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200608