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| Fig. 1: The La Hague Facility (Source: Wikimedia Commons) |
While nuclear energy has been championed as one of the leading alternative energy sources in the 21st century in our fight against man-made climate change, the reprocessing and disposal of spent nuclear fuel has remained a challenge for much of the world. The primary source of fissile material for nuclear energy in the world is currently uranium, specifically U-235 for light water reactors. However, these fuels present a significant challenge after they have been used and depleted in nuclear reactors. Not only are they unable to continue to supply power, they also contain high amounts of radioactive material. For countries that uses a large amount of nuclear energy, this is a major problem as the spent fuel has to be either recycled or disposed. While in the U.S, the majority of the nuclear waste are disposed, many other parts of the world, such as Japan and France, chose to reprocess and recycle these materials. The La Hague nuclear reprocessing facility in France (Fig. 1) was built in order to address this problem.
Originally commissioned in 1966 for military nuclear applications for the production of plutonium for the French Nuclear Program, it was switched over to reprocess spent nuclear fuels in 1976 following the global oil crisis. [1] The oil crisis launched nuclear power into the forefront of alternative energy sources due to their perceived isolation from the geopolitics of OPEC. Incidentally, it had also created the sudden urgency for nuclear recycling. Because uranium was a non-renewable resource, it was thought that a heavy reliance on nuclear power could deplete Uranium reserves in a matter of decades. Thus the La Hague plant was conceived in order not only reduce the amount of nuclear waste, but to also conserve the amount of raw Uranium needed for nuclear power. The La Hague plant would reprocess and recycle by separating out plutonium and uranium from spent nuclear fuel rods in order to provide materials for a proposed fleet of fast breeder reactors using a mix of unenriched uranium and plutonium as fuel. [2] These reactors would yield an additional 50-100 times the original energy supplied by the amount of raw uranium that went through the light water reaction cycle. [3] Ultimately, the technology for fast breeder reactors never achieved commercial success due to difficulties with liquid metal cooling corrosion. Nontheless the La Hague project became the centerpiece of French nuclear reprocessing and recycling. [4] The facility processes not only French domestic nuclear waste, but it also processes much of the nuclear waste from the neighboring countries. The current two active plants at La Hague, UP2 and UP3, has a combined of 1700 THM per year (tons of heavy metal). [5]
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| Fig. 2: A process flow diagram showing the steps of the PUREX process. (Source: P. Wang) |
Nuclear recycling and reprocessing allows for the recovery of actinide elements from spent nuclear fuel. [6] This not only reduces the need to mine new rare actinide minerals which are not a renewable resources, and reduces the volume of waste that is must be disposed. In light-water reactors such as the Pressurized Water Reactors (PWRs) used in France, the original nuclear fuel was enriched to a higher than natural amount of U-235. The reaction process then gradually decreases the fraction of U-235 in the fuel rods until until the material is no longer suited for light-water reactors. At that point, the nuclear material is then transported to a reprocessing and recycling facility to be treated.
Out of all the material components of the fuel assembly, 94-96% of the mass can be recycled using La Hague's current process.
The PUREX process (Plutonium Uranium Refining by Extraction, shown in Fig. 2) is utilized by both of the UP2 and UP3 plants at the La Hague facility. This process recovers 99.5% of the uranium and plutonium in the spent fuel rod assembly. [4] The PUREX process at the La Hague plants follows the following processes. [7] First, the spend fuel rods are cooled for no less than 5 years. Then the fuel rod assembly is mechanically broken down into smaller pieces and dissolved in nitric acid. This allows actinide metals such as uranium, plutonium, as well as other fission byproducts to dissolve into the solution. Volatile gases are siphoned off and treated in order to remove radioactive fission byproducts.
The dissolved solution is then concentrated and undergoes a solvent extraction process. By controlling the pH levels as well as the valence states of the metals in solution, minor actinides (actinides other than uranium and plutonium) are first separated out from the solution. Then the Uranium and Plutonium are separated from each other by manipulating the plutonium valence state. The purified separated stream of aqueous uranium is dried through direct thermal denitration while the plutonium stream is then converted into solid state through oxalate precipitation and calcination.
The waste solution containing the minor actinides and other fission waste products undergoes evaporation and calcination before finally going into the waste disposal cycle. In the waste disposal cycle, the materials are separated in low-level waste and high-level waste. The low-level waste is compacted and stored in stainless steel containers. All high-level radioactive waste is vitrified into a glass matrix as to ensure their long term storage stability.
The La Hague reprocessing and recycling facility, like many other nuclear energy projects around the globe, has also been the subject of many criticisms throughout its operating life.
One of the first criticism comes from the danger of nuclear proliferation. The PUREX process extracts plutonium from spent enriched uranium reactors. This plutonium can be directly used in creating a plutonium based nuclear weapon. In fact, the original plan for La Hague was to create plutonium for France's nuclear arsenal. Not only does plutonium have more desirable cross section characteristics for nuclear weapons, it is also much easier to mask the production of plutonium under the guise of legitimate spent fuel reprocessing and recycling. This concern for nuclear proliferation was what stopped many of the nuclear recycling and reprocessing efforts in the United States.
Another concern is that the plant proposes environmental challenges. Due to plant operation, certain low-level radioactive liquids are discharge into the North Sea. However, the total radioactivity of the plant operation contributes to 5% of the total dose from all industrial discharge in the North Sea, with oil and gas operations, and phosphate mining contributing to 35% and 55% respectively. [4]
The La Hague has safely processed spent nuclear fuel from various nuclear power plants around the world in the past 40 years. It demonstrates that the reprocessing and recycling of spent nuclear fuel can be economically viable, and ecologically sound. As a new generation of fast breeder reactors are being investigated, La Hague is also investigating how to further reduce their actinide disposal by creating new types of fuels that can be used by Gen IV fast breeder reactors. [3]
© Peter Wang. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] Kaplan, "Status and Prospects for Spent Fuel Management in France," in Spent Fuel Management: Current Status and Prospects 1997, International Atomic Energy Agency, IAEA-TECDOC-1006, March 1998, p. 27.
[2] P. Fairley, "Nuclear Wasteland," IEEE Spectrum 44, No. 2, 38 (2007).
[3] "Treatment and Recycling of Spent Nuclear Fuel," Commissariat à l'Énergie Atomique, 2008.
[4] "Spent Fuel Reprocessing Options," International Atomic Energy Agency, IAEA-TECDOC-1587, August 2008.
[5] D. Greneche, "Reprocessing and Recycling of Used Nuclear Fuels."
[6] J. J. Laidler et al., "Development of Pyroprocessing Technology," Prog. Nucl Energy 31, 131 (1997).
[7] "Status Report on Structural Materials For Advanced Nuclear Systems," Nuclear Energy Agency, NEA No. 6409, 2013.
