United States Nuclear Regulatory Commission - Protecting People and the Environment

Frequently Asked Questions About Mixed Oxide Fuel

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See also the Backgrounder on Mixed Oxide Fuel for more information

Index to All Frequently Asked Questions Pages

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What is mixed oxide (MOX) fuel?

The mixed oxide fuel proposed by Shaw AREVA MOX Services (formerly Duke COGEMA Stone & Webster (DCS)) is a blend of plutonium dioxide and depleted uranium dioxide that will be used as fuel in commercial nuclear power plants. Depleted uranium is a byproduct of the uranium enrichment process. Plutonium dioxide will be extracted from retired nuclear weapons and other sources of surplus plutonium. The purpose of manufacturing MOX fuel is to meet the goals of the U.S. Department of Energy's Surplus Plutonium Disposition Program. Under this program, DOE will reduce the inventory of fissile material from nuclear weapons by converting approximately 34 metric tons of surplus weapons grade plutonium into MOX fuel for use in commercial nuclear power plants. The process of converting the fissile material into MOX fuel renders the plutonium less attractive for use in nuclear weapons. In some countries, MOX fuel is manufactured by recycling plutonium from spent nuclear fuel. That is not the case in the proposed MOX program in the U.S.

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Why was Savannah River Site chosen as the location for the MOX fuel fabrication facility?

The Savannah River Site was selected by the Department of Energy. As part of the selection process, the DOE prepared an Environmental Impact Statement (EIS) and solicited public input through meetings and comments on the EIS.

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Is MOX fuel currently produced in the U.S. or elsewhere?

MOX fuel is not currently being produced in the U.S., but several European countries have been producing MOX fuel for more than 20 years. Their supply of plutonium is from spent nuclear fuel rather than nuclear weapons. Under agreements between Russia and the U.S., Russia also plans to build and operate a MOX fuel fabrication facility in Russia to reduce its surplus plutonium stockpile.

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What is NRC's regulatory responsibility for MOX?

Congress assigned responsibility for licensing the proposed DOE MOX fuel fabrication facility to NRC. Two NRC offices have regulatory responsibility for MOX. The Office of Nuclear Material Safety and Safeguards will be responsible for licensing the proposed MOX fuel fabrication facility, which is intended to make fuel assemblies for commercial power plants. NRC's Office of Nuclear Reactor Regulation (NRR) will be responsible for licensing the use of the MOX fuel in commercial power plants.

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How does the uranium fuel cycle produce depleted uranium?

The uranium nuclear fuel cycle consists of several processes involving uranium in different chemical and physical forms. Natural uranium contains 0.7 percent of the uranium-235 (U235) isotope. At uranium enrichment facilities, the gas centrifuge enrichment process uses the flow of gas through spinning cylinders (i.e., centrifuges) to produce uranium that is enriched to a higher concentration of U235. The enrichment process also produces uranium depleted in U235 as a by-product. Depleted uranium typically has about 0.3 percent U235. This depleted uranium, combined with the plutonium from retired U.S. nuclear devices and other surplus plutonium, forms MOX fuel.

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How is MOX fabricated?

Plutonium dioxide is mixed with depleted uranium dioxide to form mixed oxide powder. This powder is pressed and bonded into pellets through a heating process called sintering. The pellets are then loaded into corrosion-resistant thin metal tubes called fuel rods. The rods are bundled into fuel assemblies that are shipped to power plants licensed to use MOX fuel. MOX fuel assemblies will be shipped to the reactors in transportation containers that have undergone a thorough safety evaluation and are licensed by the NRC for this purpose.

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Would MOX fuel be used in reactors in the same way that uranium fuel is now used?

NRC believes that MOX fuel could be used in a reactor if it performs in a way very similar to current fuel. Although the reactors were not specifically designed to use weapons-grade plutonium, they were designed to use the reactor-grade plutonium that is generated in the uranium fuel during normal operation. There is substantial world-wide experience with the use and behavior of reactor-grade plutonium, because all operating reactors contain plutonium created during the fission process.

If approved by NRC, the reactor licensee would test the MOX fuel by first operating with a few "lead test assemblies" in the reactor for at least two operating cycles. MOX fuel is tested in the reactor to verify the ability of the models to predict fuel performance and the applicability of the European database to the U.S. MOX fuel.

After approval by the NRC, the reactor licensee would insert a maximum of 40 percent of the reactor core with MOX fuel.

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What is the difference between weapons-grade plutonium and reactor-grade plutonium?

The main difference between weapons-grade plutonium and reactor-grade plutonium is the percentage of the different isotopes of plutonium. Weapons-grade plutonium contains a higher percentage of the isotope plutonium-239 than reactor-grade, while reactor-grade plutonium has more plutonium-240 than weapons-grade. Weapons-grade plutonium is more fissionable but reactor-grade is more radioactive. However, both require safe handling and that will be the focus of NRC's review.

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Would MOX fuel be reprocessed?

The United States does not currently reprocess commercial nuclear fuel (a small quantity of used fuel was reprocessed at the West Valley site in the 1960s). Reprocessing of used fuel involves the chemical treatment of the fuel to separate unused uranium and plutonium from radioactive fission products. Theoretically, uranium could be recycled through an enrichment facility and some recovered plutonium could be used in new fuel assemblies. Under the agreement with the Russians, the U.S. Government has stated that it will not reprocess the used MOX fuel.

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How would used MOX fuel be stored?

Interim Storage. NRC expects no significant difference in the way used MOX fuel and used uranium fuel is stored. After fuel has been in a reactor for two operating cycles, the fuel is stored in fuel pools or storage casks located at each reactor site. In the United States, used fuel will remain in interim storage until a high-level waste storage facility is available. For more information, see Storage of Spent Nuclear Fuel.

High-Level Waste Disposal. If a Federal high-level waste storage facility is licensed, used fuel assemblies, including MOX fuel assemblies (if available), would be packaged directly into special containers designed for the high-level waste storage facility. The containers would be shipped by truck or rail to the high-level waste storage facility, using NRC-approved shipping packages. High-level waste includes used reactor fuel and liquid wastes resulting from milling. Used fuel from nuclear power plants is one of the primary sources of high-level waste. For more information, see High-Level Waste Disposal, the Yucca Mountain Review Plan, and the Review of DOE's High-Level Waste Repository Site Recommendation.

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Will the Price-Anderson Act apply to the MOX facility? Who will be liable if an accident occurs and who will be liable for future clean-up costs?

The Price-Anderson Act will apply to the MOX fuel fabrication facility. Pursuant to provisions of the Price-Anderson Act, NRC staff understands that DOE intends to indemnify MOX Services for any damages due to accidents, clean-up costs, or other similar expenses which involve the risk of public liability connected with the MOX project at the Savannah River Site. Using MOX fuel in a reactor would not violate the Price-Anderson Act.

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As the NRC is responsible only for commercial uses of nuclear material, at what point does the plutonium from weapons become commercial?

DOE would retain jurisdiction over the plutonium during the pit disassembly and conversion process, where the weapons-grade plutonium would be purified and converted into plutonium oxide powder. When the plutonium oxide powder is transferred to the proposed MOX fuel fabrication facility to be fabricated into fuel, MOX Services would take possession, subject to NRC regulations, but the material would still be owned by the DOE. The reactor licensee assumes ownership of the material when the fresh fuel assembly is placed in the reactor.

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With regard to protecting the public health and safety, is the DOE responsible to the NRC?

The NRC has responsibility for civilian use of nuclear material. In cases where nuclear material is used for military purposes, the NRC has no authority over the DOE beyond the specific activities listed for regulation by the NRC under the Energy Reorganization Act (Section 202). However, Congress has assigned the NRC regulatory authority over activities at a MOX fuel fabrication facility, if it is built and operated. DOE would own the facility. MOX Services would construct and operate the facility for the DOE and would be subject to NRC regulatory authority. Safe and secure handling of licensed material would be the responsibility of MOX Services.

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Who has the ultimate authority over the proposed MOX facility?

The responsibility for ensuring that the facility is designed, constructed, and operated safely resides with the facility operator: MOX Services. NRC's role is to provide sufficient oversight and regulation to ensure that public health and safety, the common defense and security, and the environment remain protected. DOE also oversees the MOX facility because MOX Services is a contractor for the Department.

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Page Last Reviewed/Updated Wednesday, February 08, 2017