Everything You Always Wanted To Know About MOX Fuels
- By Duncan Williams -
Last week a nuclear reactor in Genkai, Japan, became the first Japanese nuclear reactor to use a type of nuclear fuel known as mixed-oxide (MOX) fuel. Although uncommon in Japan and America, MOX fuel is currently used in at least 30 reactors throughout Europe, and is proving to be a rapidly growing niche in the nuclear industry. Conventional nuclear fuel includes a single oxide of enriched uranium-235. But MOX fuels contain a mixture of more than one oxide, such as an oxide of uranium-238 and an oxide of plutonium. Uranium-238 is also known as depleted uranium, and must undergo a costly enrichment process in order to become uranium-235. Uranium-238 is not radioactive, and is often used as shielding against radioactivity due to its high density. Depleted uranium is much cheaper than uranium-235 partly because 99% of all naturally occurring uranium exist in the form of uranium-238.
Although depleted uranium is much less expensive than enriched uranium, depleted uranium is not fissile – meaning it is too stable to sustain a long-term fission reaction in a nuclear reactor. Plutonium, on the other hand, is a fissile element and capable of sustaining long-term nuclear fission. Only a small amount of plutonium is needed to make MOX fuel – the typical ration is 5% -10% plutonium with the remainder consisting of uranium-238. The plutonium used in MOX fuel can come from either reprocessing spent nuclear fuel (from nuclear reactors) or from reprocessing dismantled nuclear weapons.
The U.S. Department of Energy (DOE) sees much promise in the technology of turning nuclear warheads into nuclear fuel. So much, in fact, that it authorized the construction of a $4.86 billion MOX Fuel Fabrication Facility in 1999 near Aiken, South Carolina. Known as the Savannah River Site, weapons-grade plutonium will be processed into nuclear fuel which can then be used in conventional nuclear reactors all across America.
A recently published patent application suggests that MOX fuels, such as those produced at the Savannah River Site, can be used in existing conventional nuclear reactors with little to no modifications to the reactor design. U.S. Patent Publication No. 20080181350, owned by Nuclear Fuel Industries, Ltd., indicates that MOX fuel has insubstantial negative effects on the operation of a conventional nuclear reactor if less than half the enriched uranium-235 fuel is substituted with MOX fuel. This publication also suggests that MOX fuel can be formed having different densities, so that the more dense nuclear fuel can be placed in the center of the reactor core to ensure proper long-term operation.
The Savannah River Site will base its process of manufacturing MOX fuels on the process Areva currently uses in its MOX fuel facilities in France. But instead of extracting plutonium from dismantled nuclear weapons, Areva’s facilities in France extract plutonium from spent nuclear fuel from nuclear reactors. The Department of Energy has indicated there are no plans to reprocess used nuclear fuel in order to extract plutonium for MOX fuel. This is significant because Areva’s process is France is directed towards extracting “reactor-grade” plutonium, while the Savannah River Site’s process will focus on extracting “weapons-grade” plutonium. Not only is weapons-grade plutonium of a higher purity than reactor-grade plutonium, but the plutonium coming from spent nuclear fuel includes many other impurities from fission products as a result of being irradiated for years inside a nuclear reactor. Thus, the method used by Areva’s facilities in France may need some adjustments when manufacturing MOX fuel at the Savannah River Site.
Shaw Areva MOX Services, LLC, is the prime contractor responsible for the design, construction, and operation of the Savannah River Site. As can be seen in the diagram from Shaw Areva MOX Services’s web site, the overall process that will be used at the Savannah River Site consists of two stages: the aqueous polishing stage and the MOX process stage. In the aqueous polishing stage, impurities are removed from the plutonium in order to produce polished plutonium dioxide. The MOX process blends the uranium dioxide and the plutonium dioxide together into a pellet form, which is then stacked inside hollow metal rods known as a fuel assembly.
The process described in the diagram seems to mimic a process known as Plutonium Uranium Refining by Extraction, or PUREX, which is widely used today to extract plutonium from spent nuclear fuel. The first step in this process is to dissolve the spent nuclear fuel in nitric oxide. Once the spent nuclear fuel is in a liquid state, tributyl phosphate is added which then isolates the plutonium from other impurities such as gallium and americium. These impurities are removed leaving only polished (or pure) plutonium. This process is described in more detail in U.S. Patent Publication No. 20090184298, published on July 23, 2009.
But these processes relate to processing plutonium from spent nuclear fuel, and does not account for the fact that the plutonium at the Savannah River Site will be extracted from a nuclear weapon. Since construction at the Savannah River Site will not be completed until 2016, there is still time to develop technology for converting weapons-grade plutonium into MOX fuel.
For example, U.S. Patent No. 7,070,717, owned by Belgonucleaire (a Belgium corporation), describes a process for creating MOX fuel from plutonium taken specifically from nuclear weapons. This patent, issued on July 4, 2006, indicates that using a wet process to remove impurities, similar to the process to be used at the Savannah River Site, is disadvantageous because it creates a large amount of liquid waste. Instead, the patent describes a dry method of removing impurities from the plutonium, and minimizes the resulting liquid waste. The element gallium is used in deconstructing plutonium weapons, and exists in small concentrations in the plutonium dioxide after the weapon has been dismantled. The method described here removes the gallium, as well as other impurities, without the creation of any additional liquid waste.
It seems that converting weapons-grade plutonium into MOX fuels would simultaneously reduce stockpiles of nuclear weapons while providing needed electricity to America’s power grid. However, several MOX fuel fabrication facilities in other countries have failed miserably.
For example, the Sellafield MOX Plant in England, completed in 1997, was designed to produce 120 tons of MOX fuel yearly. But due to technical difficulties it only produced 5 tons of MOX fuel in its first 5 years of operation. Last year, Britain’s Energy Minister Malcom Wiks admitted that the Sellafield MOX plant was one of the most catastrophic failures in British industrial history. The Sellafield plant is currently being decommissioned.
Similarly, Belgium MOX fuel producer Belgonucleaire SA had to decommission its MOX fuel plant in 2006 based on changing market conditions. Reasons for the closure cited by Belgonucleaire include the Belgium government deciding against using any further MOX fuels in its reactors, and Germany enacting a ban on MOX fuels in its reactors in 2005. These factors, in addition to an increasingly competitive marketplace in the MOX fuel industry, forced Belgonucleaire to decommission its plant.
Not only will the Savannah River Site be the first MOX fuel fabrication facility in America, it will be the only facility in the world that converts nuclear warheads into nuclear fuel for reactors. This would be a significant milestone not only in American history, but in global history. However, Shaw Areva MOX Services must ensure its technology will allow it to avoid the missteps of the failed MOX fuel facilities in other countries.
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About Duncan Williams
Duncan Williams graduated from the University of Florida in 1994 with a B.S. in Physics, and a minor in mathematics. Upon graduation, he was commissioned in the U.S. Navy where he completed training in the Navy’s Nuclear Propulsion program. He then served onboard an 
aircraft carrier, the USS Theodore Roosevelt, as a reactor control division officer. Onboard, he was responsible for the operation and maintenance of the electrical and mechanical components that make up the reactor control systems. This includes the control rod drive mechanisms, the reactor safety and emergency systems, the reactor coolant pump systems, and the ion exchangers. He also developed and implemented ship-wide reactor safety drills in order to educate sailors in reactor safety.
Duncan then transferred to the U.S. Naval Academy, where he served as a senior instructor teaching Thermodynamics to senior cadets. While serving as an instructor at the Naval Academy, Duncan attended night law school at the George Washington University Law School. After receiving his J.D. in 2004, he resigned his commission and began working as an intellectual property associate with Kenyon & Kenyon LLP. While at Kenyon & Kenyon, he drafted numerous patents relating to medical devices, electronic devices, telecommunications, as well as other technologies. He also has experience in all stages of patent litigation, and has represented numerous Fortune 500 companies in protecting their intellectual property rights. Duncan is currently an intellectual property associate at Blank Rome LLP.
If you have questions, comments, or know of a patent that you think Duncan should review E-mail Duncan Williams>> duncan@nuclearstreet.com