The Future Should Be Through The Viewport On An Asteroid

The Future Should Be Through The Viewport On An Asteroid
Asteroid P/2010 A2 | Credit: NASA, ESA, and D. Jewitt (UCLA)

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Saturday, March 21, 2015

Space Exploitation: Powering Space VI - Integral Fast Reactor (IFR)

IFR Concept
Argonne National Laboratory-West

The expanded era of space exploitation will require large amounts of energy, especially in the form of electrical power. Determining, considering and evaluating the various options available for power in space is essential, especially for large-scale space-based endeavor. While many nuclear power options are restricted to the later era of space exploitation, especially due to size and mass restrictions, some nuclear alternatives may be small enough for implementation in the early era of space exploitation. One curious form is the Integral Fast Reactor (IFR), a type of sodium-cooled fast breeder reactor. While the reactor design itself may not be ideal for space exploitation, many of the design details and concepts within may prove quite valuable for space-based endeavor, especially the focus on recycling spent nuclear fuel.

Table: 900 MWth IFR Core Design Parameters
D. C. Wade and Y. I. Chang

IFR is a type of advanced liquid-metal reactor that relies on fast neutrons within its power generation cycle. The IFR has four specific technical features, which are liquid sodium cooling, a pool-type reactor configuration, metallic fuel, and an integral fuel cycle. The fuel cycle relies on pyrometallurgical processing, as well as an injection-cast fuel fabrication, with the fuel cycle facility able to collocate with the reactor. IFR has a focus on the reprocessing of nuclear fuel, which it achieves through the pyrometallurgical processing.

IFR Pyrometallurgical Processes for Core and Blanket
D.C. Wade and Y.I. Chang | Argonne National Laboratory
Pyroprocessing is a fanciful technical term for subjecting materials to high temperatures, in order to achieve a chemical or physical change; Cement manufacturing, for example, is a type of pyroprocessing. Pyrometallurgy is a type of extractive metallurgy, in which heat is used to enact physical and/or chemical transformations in ore, or any other underlying material, in order to extract desirable metals. In context, injection casting is the formation of fuel slugs via advanced pyroprocessing of nuclear material, which in turn inserted and seal welded into sodium-bonded cladding. Proponents and researchers of IFR argue that its pyroprocessing system is very useful for reprocessing, because it can separate actinide elements which occur alongside plutonium product stream outputs. The particularly hard neutron cross-section for IFR is also considered very effective for burning actinides.

A part of the pyrometallurgical process is electrorefining, which is the electrodeposition of metals from their ores, through processing said ore in solution, which itself is known as leaching. Electrofining is alternatively known as electrowinning or electroextraction. In IFR, electrorefining is an intensive process, and is a key component of the IFR fuel recycling cycle. The spent core or blanket fuel rods are sliced into segments, with their cladding intact, with thermal-bond sodium and alkali fission products recovered from the segments. A batch of the fuel segments are placed into perforated steel baskets, which are then taking to an electrofiner, which engages electrorefining. The fuel segments are subjected to a high temperature salt-based solution, with Uranium and Plutonium deposited in metallic forms onto cathodes during this process. The cathode from the surrounding fuel blanket is subjected to halide slagging, in order to separate plutonium rich fuel feed, in order to refabricate this fuel for the primary fuel driver. This fuel is set into fuel slug form using injection casting.

EBR-II Primary Tank
Federal Government of the United States

The IFR is based on the Experimental Breeder Reactor (EBR) II, which is a prototype sodium-cooled reactor with a power rating of 62.5 Thermal Megawatts. The EBR-II is a curious nuclear historical artifact, as it was tested under very intensive conditions of catastrophic failure. In April of 1986, the reactor was operated at full power, with emergency shutdown system disabled, and the main primary cooling pumps were shut down to stress-test the system. The reactor dropped to near-zero operability within approximately 300 seconds, with no damage to the reactor. Another test was conducted, with secondary cooling systems halted, while the reactor was a full power. Although there was a temperature increase, the expansion of the fuel and coolant led to a reactor shutdown instead of a meltdown, which indicated that the system was able to make use of inherent safety features, such as thermal expansion, rather than explicit safety constraints.

PRISM Reactor
U.S. Nuclear Regulatory Commission

There has been attempts to commercialize IFR technology. One such attempt has been made by GE Hitachi Nuclear Energy (GEH), in the form of the Power Reactor Innovative Small Module (PRISM). The PRISM is nearly identical in many ways to the EBR-II, although the reactor is intended to be modular in design, with a power output of 311 Thermal Megawatts. The reactor has an additional safety feature, in the form of Reactor Vessel Air Cooling System (RVACS), which is a passive air cooling system intended to remove decay heat.

BN-800 Reactor
Source (Russia)

A variant of IFR is the Sodium-Cooled Fast Reactor (SFR), which has been combined in terms of design principle with the Liquid Metal Fast Breeder Reactor (LMFBR). An example of a commercially operational SFR is the BN-800 reactor, which is a sodium-cooled fast breeder reactor. It is located at the Beloyarsk Nuclear Power Station in Zarechny Sverdlovsk Oblast, Russia. It is a plutonium cycle breeder, and burns mixed uranium-plutonium fuel, with an intent to generate 880 MW worth of power. Similar to the IFR, the BN-800 is a pool-type reactor, which the reactor, coolant pumps, intermediate heat exchangers and associated infrastructure and piping located in a pool of liquid sodium. The BN-800 Reactor began initial operation in mid 2014, and has starting ramping up as of the end of 2014. China has expressed interest in the BN-800 design, and evidently signed an agreement with Russia to purchase the design once the BN-800 proved its effectiveness, although this was considered to be somewhat tentative as of 2012.

IFR Fuel Cycle
Source

Although solar cells are most definitely the immediate future of space exploration, as well as the very near future of space exploitation, a reactor design intended specifically for recycling nuclear may be valuable, especially in the middle to late portion of space exploitation, when nuclear power will be rather prevalent in the outer solar system. While heat dissipation is a significant issue with any form of nuclear power in space, the notion of recycling nuclear waste for power generation is not only useful - it is also sensible and efficient, as it reduces net nuclear waste. For space exploitation and advanced space exploration, such reactors might be very useful for automated facilities and manufacturing centers, especially those which might have few human staff members.

For it is through innovationcost-reductions and radical technologies that humanity will achieve the dream of a space-based civilization, initially as a mining endeavor in the Near-Earth environment, and then onward to settlement and colonization of the entire Solar system.