Gaseous fission reactor
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A limitation for conventional nuclear fission reactors is that if the nuclear fuel temperature were to rise too high in temperature, the Nuclear reactor core would melt. However, if the reactor core was gaseous, the only temperature limiting materials would be the reactor walls. It may also be possible to confine gaseous fission fuel magnetically in the reactor so that it does not touch and melt the reactor walls. A potential benefit of the gaseous reactor core concept is that instead of relying on the traditional rankine or brayton conversion cycles, it may be possible to extract electricity magnetohydrodynamically, or with direct conversion of the charged particles.
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[edit] Theory of operation
The vapor core reactor (VCR), also called a gas core reactor (GCR), has been studied for some time. It would have a gas or vapor core composed of UF4 with some 4He and/or 3He added to increase the electrical conductivity, the vapor core may also have tiny UF4 droplets in it. It has both terrestrial and space based applications. Since the space concept doesn’t necessarily have to be economical in the traditional sense, it allows the enrichment to exceed that which would be acceptable for a terrestrial system. It also allows for a higher ratio of UF4 to helium, which in the terrestrial version would be kept just high enough to ensure criticality in order to increase the efficiency of direct conversion. The terrestrial version is designed for a vapor core inlet temperature of about 1500 K and exit temperature of 2500 K and a UF4 to helium ratio of around 20% to 60%. It is thought that the outlet temperature could be raised to that of the 8000 K to 15000 K range where the exhaust would be a fission-generated non-equilibrium electron gas, which would be of much more importance for a rocket design. A terrestrial version of the VCR’s flow schematic can be found in reference 2 and in the summary of non-classical nuclear systems in the second external link. The space based concept would be cut off at the end of the MHD channel.
[edit] Reasoning for He-3 addition
3He may be used in increase the ability of the design to extract energy and be controlled. A few sentences from Anghaie et al. sheds light on the reasoning:
- "The power density in the MHD duct is proportional to the product of electrical conductivity, velocity squared and magnetic field squared σv²B². Therefore, the enthalpy extraction is very sensitive to the MHD input-output fluid conditions. The vapor core reactor provides a hotter-than-most fluid with potential for adequate thermal equilibrium conductivity and duct velocities. Considering the product v² x B², it is apparent that a light working fluid should dominate the thermal properties and the UF4 fraction should be small. Additional electrical conductivity enhancement might be needed from thermal ionization of suitable seed materials, and from non-equilibrium ionization by fission fragments and other ionizing radiation produced by the fissioning process."[1]
[edit] See also
[edit] References
- ^ Anghaie, S., Pickard, P., Lewis, D. (unknown date). Gas Core & Vapor Core Reactors- Concept Summary
- Brown, L.C. (2001). Direct Energy Conversion Fission Reactor: Annual Report For The Period August 15, 2000 Through September 30, 2001
- Knight, T. (unknown date) Shield Design for a Space Based Vapor Core Reactor [online] available: http://www3.inspi.ufl.edu/icapp/program/abstracts/1174.html
