Since steep temperature gradients will be present in any such gas core reactor, several implications for neutronics must be considered. The open-cycle gas-core reactor (OCGCR) is typically a thermal/epithermal reactor. Most types of OCGCR require external moderation due to the steep temperature gradients inside the gaseous core. Neutrons born in the fuel region travel relatively unimpeded to the external moderator where some are thermalized and sent back into the gas core.
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All gas- core reactor rocket designs share several properties in their nuclear reactor cores, and most designs share the same materials. The closest terrestrial design concept is the gaseous fission reactor.
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There are two main variations of the gas core reactor rocket: open cycle designs, which do not contain the fuel within a vessel, and closed cycle designs, which contain the gas reaction core within a solid structure.
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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 (UF4) with some helium (4He) 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 what would be acceptable for a terrestrial system.
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A PARR-II consists of a core reactor, control rod, and nuclear reflectors, and it is enclosed in a water-tight cylindrical Al13 alloy vessel. The nuclear reactor core is an under-moderated array with 1H to 235U ratio of temperature of 20 °C and provides a strong Negative temperature coefficient and thermal volume coefficients of reactivity. The PAEC scientists and engineers also built and constructed the nuclear accelerator on 9 April 1989. The particle accelerator is heavily used to conduct research in nuclear technology.
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At high temperatures, heat is transferred predominantly by thermal radiation (rather than thermal conduction). However, the hydrogen gas used as propellant is almost completely transparent to this radiation. Therefore, in most gas core reactor rocket concepts, some sort of seeding of the propellant by opaque solid or liquid particles is considered necessary. Particles of carbon [soot] (which is highly opaque and remains solid up to 3915 K, its sublimation point) would seem to be a natural choice; however, carbon is chemically unstable in a hydrogen-rich environment at high temperatures and pressures.
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Diagram of a "nuclear lightbulb"–style closed cycle gas core reactor rocket. The closed cycle is advantageous because its design virtually eliminates loss of fuel, but the necessity of a physical wall between the fuel and the propellant leads to the obstacle of finding a material with extremely optimized characteristics. One must find a medium that is transparent to a wide range of gamma energies, but can withstand the radiation environment present in the reactor, specifically particle bombardment from the nearby fission reactions. This barrage of particles can lead to sputtering and eventual wall erosion.
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Liquid core nuclear engines are fueled by compounds of fissionable elements in liquid phase. A liquid-core engine is proposed to operate at temperatures above the melting point of solid nuclear fuel and cladding, with the maximum operating temperature of the engine instead being determined by the reactor pressure vessel and neutron reflector material. The higher operating temperatures would be expected to deliver specific impulse performance on the order of 1300 to 1500 seconds (12.8-14.8 kN·s/kg). A liquid-core reactor would be extremely difficult to build with current technology.
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A gas nuclear reactor (or gas fueled reactor or vapor core reactor) is a proposed kind of nuclear reactor 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 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.
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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.
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Gas core reactor rockets are a conceptual type of rocket that is propelled by the exhausted coolant of a gaseous fission reactor. The nuclear fission reactor core may be either a gas or plasma. They may be capable of creating specific impulses of 3,000–5,000 s (30 to 50 kN·s/kg, effective exhaust velocities 30 to 50 km/s) and thrust which is enough for relatively fast interplanetary travel. Heat transfer to the working fluid (propellant) is by thermal radiation, mostly in the ultraviolet, given off by the fission gas at a working temperature of around 25,000 °C.
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A nuclear thermal rocket can be categorized by the type of reactor, ranging from a relatively simple solid reactor up to the much more difficult to construct but theoretically more efficient gas core reactor. As with all thermal rocket designs, the specific impulse produced is proportional to the square root of the temperature to which the working fluid (reaction mass) is heated. To extract maximum efficiency, the temperature must be as high as possible. For a given design, the temperature that can be attained is typically determined by the materials chosen for reactor structures, the nuclear fuel, and the fuel cladding.
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The first electrical power was produced on December 18, 1957 as engineers synchronized the plant with the distribution grid of Duquesne Light Company. The first core used at Shippingport originated from a cancelled nuclear-powered aircraft carrier and used highly enriched uranium (93% U-235) as "seed" fuel surrounded by a "blanket" of natural U-238, in a so-called seed-and-blanket design; in the first reactor about half the power came from the seed.J. C. Clayton, "The Shippingport Pressurized Water Reactor and Light Water Breeder Reactor", Westinghouse Report WAPD-T-3007, 1993 The first Shippingport core reactor turned out to be capable of an output of 60 MWe one month after its launch.
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Nuclear gas core closed cycle rocket engine diagram, nuclear "light bulb" A nuclear lightbulb is a hypothetical type of spacecraft engine using a gaseous fission reactor to achieve nuclear propulsion. Specifically it would be a type of gas core reactor rocket that uses a quartz wall to separate nuclear fuel from coolant/propellant. It would be operated at temperatures of up to 22,000°C where the vast majority of the electromagnetic emissions would be in the hard ultraviolet range. Fused silica is almost completely transparent to this light, so it would be used to contain the uranium hexafluoride and allow the light to heat reaction mass in a rocket or to generate electricity using a heat engine or photovoltaics.
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Nuclear gas-core-reactor rockets can provide much higher specific impulse than solid core nuclear rockets because their temperature limitations are in the nozzle and core wall structural temperatures, which are distanced from the hottest regions of the gas core. Consequently, nuclear gas core reactors can provide much higher temperatures to the propellant. Solid core nuclear thermal rockets can develop higher specific impulse than conventional chemical rockets due to the low molecular weight of a hydrogen propellant, but their operating temperatures are limited by the maximum temperature of the solid core because the reactor's temperatures cannot rise above its components' lowest melting temperature. Due to the much higher temperatures achievable by the gaseous core design, it can deliver higher specific impulse and thrust than most other conventional nuclear designs.
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With the threat of GLaDOS quenched, Wheatley prepares to send Chell to the surface, but he becomes power-hungry due to GLaDOS' core programming; he places GLaDOS' personality into a module powered by a potato battery and sends her and Chell into the depths of Aperture Science. As Chell and GLaDOS fall, GLaDOS reveals that Wheatley was actually meant to be a "tumor", with the purpose of generating an endless stream of bad ideas in order to control her. While Chell and GLaDOS work their way up from deep underground, Wheatley begins fumblingly experimenting with his control of the facility, causing several key systems to fail. By the time Chell and GLaDOS arrive, the core reactor in the facility is set to overload, and the only way to stop it is for GLaDOS to retake her main unit back from Wheatley.
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