A gas nuclear reactor
(or gas fueled reactor
) limits the only temperature limiting materials in a reactor to the reactor walls. 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. It may also be possible to confine gaseous fission fuel magnetically, electrostatically or electrodynamically in the reactor so that it would 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 simple direct electrostatic conversion of the charged particles.
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 4
He and/or 3
He 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.
Reasoning for He-3 addition
He 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."
The fuel, evaporated by its self-heat to gas, is flowed around by liquid hydrogen, whereby the gas core is prevented by magnetic fields similarly as with the fusion reactor from the Auseinanderfliessen. With such an arrangement, which should be operated for reasons of the radioactive contamination of the environment only in space, very high flow-out rates can be obtained.
A container, on whose exterior a coil tapes is, is filled with gaseous uranium hexafluoride
, whose uranium is enriched. The arrangement is filled to scarce to critical measures. In a place the uranium hexafluoride is so strongly compressed by (for example by a bang cap) produced a pressure wave that a nuclear chain reaction comes. Thereby develops here an enormous heat, which leads to the expansion of the uranium hexafluoride. Since this cannot escape, it comes in other places to compressions, at which a nuclear chain reaction comes again. The result is a plasma wave moving by the container. This is surrounded by magnetic fields, which induce a tension in the coil rolled up on the container. The efficiency of this arrangement amounts to approx. 20 per cent.
With the process an enormous heat develops, why the container with the uranium hexafluoride and the coil must be flowed around by a cooling agent. With the cooling agent heated up still another conventional thermal generation of current with an efficiency can be accomplished by 35%, similarly as in today's nuclear power stations, so that with this arrangement an efficiency of 55% would be possible.
However there are enormous problems with corrosions during this arrangement, there uranium hexafluoride is chemically very reactive and it gives also enormous safety problems.
Until today still no reactor was built according to this pattern.
- 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 at archive.org