A gas nuclear reactor (or gas fueled reactor or vapor core reactor) is a proposed kind of
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...
in which the
nuclear fuel would be in a gaseous state rather than liquid or solid. In this type of reactor, the only temperature-limiting materials would be the reactor walls. Conventional reactors have stricter limitations because the
core
Core or cores may refer to:
Science and technology
* Core (anatomy), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the centra ...
would melt if the fuel temperature were to rise too high. It may also be possible to confine gaseous fission fuel magnetically, electrostatically or electrodynamically 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
uranium tetrafluoride
Uranium tetrafluoride is the inorganic compound with the formula UF4. It is a green solid with an insignificant vapor pressure and low solubility in water. Uranium in its tetravalent ( uranous) state is important in various technological process ...
(UF
4) with some
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
(
4He) added to increase the electrical conductivity, the vapor core may also have tiny UF
4 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 what would be acceptable for a terrestrial system. It also allows for a higher ratio of UF
4 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 1,500 K and exit temperature of 2,500 K and a UF
4 to helium ratio of around 20% to 60%. It is thought that the outlet temperature could be raised to that of the 8,000 K to 15,000 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-4 addition
4He 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
Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...
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 × B², it is apparent that a light working fluid should dominate the thermal properties and the UF
4 fraction should be small. Additional electrical conductivity enhancement might be needed from
thermal ionization
Thermal ionization, also known as surface ionization or contact ionization, is a physical process whereby the atoms are desorbed from a hot surface, and in the process are ionized.
Thermal ionization is used to make simple ion sources, for mass ...
of suitable seed materials, and from non-equilibrium
ionization
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...
by fission fragments and other
ionizing radiation produced by the fissioning process."
[Anghaie, S., Pickard, P., Lewis, D. (unknown date). Gas Core & Vapor Core Reactors—Concept Summary]
Spacecraft
The spacecraft variant of the gaseous fission reactor is called the
gas core reactor rocket. There are two approaches: the open and closed cycle. In the open cycle, the propellant, most likely hydrogen, is fed to the reactor, heated up by the nuclear reaction in the reactor, and exits out the other end. Unfortunately, the propellant will be contaminated by fuel and fission products, and although the problem can be mitigated by engineering the hydrodynamics within the reactor, it renders the rocket design completely unsuitable for use in atmosphere.
One might attempt to circumvent the problem by confining the fission fuel magnetically, in a manner similar to the fusion fuel in a
tokamak
A tokamak (; russian: токамáк; otk, 𐱃𐰸𐰢𐰴, Toḳamaḳ) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being ...
. Unfortunately it is not likely that this arrangement will actually work to contain the fuel, since the ratio of ionization to particle momentum is not favourable. Whereas a tokamak would generally work to contain singly ionized deuterium or tritium with a mass of two or three
daltons, the uranium vapour would be at most triply ionized with a mass of 235
dalton (unit)
The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass widely used in physics and chemistry. It is defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at ...
. Since the force imparted by a magnetic field is proportional to the charge on the particle, and the acceleration is proportional to the force divided by the mass of the particle, the magnets required to contain uranium gas would be impractically large; most such designs have focused on fuel cycles that do not depend upon retaining the fuel in the reactor.
In the closed cycle, the reaction is entirely shielded from the propellant. The reaction is contained in a quartz vessel and the propellant merely flows outside of it, being heated in an indirect fashion. The closed cycle avoids contamination because the propellant can't enter the reactor itself, but the solution carries a significant penalty to the rocket's
Isp
An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise private ...
.
Energy production
For energy production purposes, one might use a container located inside a solenoid. The container is filled with gaseous
uranium hexafluoride
Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...
, where the uranium is enriched, to a level just short of criticality. Afterward, the uranium hexafluoride is compressed by external means, thus initiating a nuclear chain reaction and a great amount of heat, which in turn causes an expansion of the uranium hexafluoride. Since the UF
6 is contained within the vessel, it can't escape and thus compresses elsewhere. The result is a plasma wave moving in the container, and the solenoid converts some of its energy into electricity at an efficiency level of about 20%. In addition, the container must be cooled, and one can extract energy from the coolant by passing it through a heat exchanger and turbine system as in an ordinary thermal power plant.
However, there are enormous problems with corrosion during this arrangement, as the uranium hexafluoride is chemically very reactive.
See also
*
Gas core reactor rocket
*
Spacecraft propulsion
References
*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
nlineavailable a
archive.org
External links
* {{Cite web , url=http://gif.inel.gov/roadmap/pdfs/non-classical_reactor_systems.pdf , title=Summary of non-classical nuclear systems , access-date=October 28, 2005 , archive-url=https://www.webharvest.gov/peth04/20041015125929/http://gif.inel.gov/roadmap/pdfs/non-classical_reactor_systems.pdf , archive-date=October 15, 2004 , url-status=dead
Nuclear power reactor types
Nuclear reactors
Nuclear technology