Re-Use of Used MOX LWR Fuel

The proposed multi-recycling scheme enabled to recycle all fuel types would likely significantly reduce the uncertainty associated with the partial-recycling strategy, including addressing net plutonium production, onsite interim storage, waste volumes, fuel supply security, and positive social impact.
Sven Bader: Orano Federal Services LLC
Cécile Evans, Philippe Valbuena: Orano SA, Etablissement MELOX

June 14, 2023
ANS Annual Meeting


Orano's La Hague Reprocessing Plant in France has processed over 40,000 metric tons (MT) of used nuclear fuel (UNF) since 1976, of which over 10,000 MT was UNF for foreign clients. Over this time Orano has continuously enlarged its industrial scope and capacities through innovation and research & development (R&D).

Recent R&D has led to multiple potential approaches to the re-use of used MOX LWR fuel to address the questions of:
  1. what to do with used MOX fuel in the absence of recycling and subsequent use in advanced (fast) reactors;

  2. what to do with the growing quantities of used MOX fuel accumulating at LWR sites;

  3. how can advanced reactors potentially benefit from recycled used MOX fuel;

  4. how can the plutonium vector continue to be degraded in MOX fuel and limit the overall accumulation of plutonium?

Two R&D approaches are presented here for the re-use of used MOX fuel with one approach now being implemented at the Borssele Nuclear Power Station (NPS) in the Netherlands and the other approach being examined for potential use in some small modular reactors (SMRs) deployed overseas.


In the first approach to the recycling of used MOX fuel, the Borssele NPS (a 500 MWe PWR [1]) first receives an advance ("loan") of plutonium from Orano for fabrication into MOX fuel for this reactor. Under this approach, the plutonium recovered from the recycling of the fuel from the final operating cycle of the reactor is the payment of the "loan" back to Orano and the shutdown Borssele NPS will not have any UNF as it all will have been recycled (including the used MOX fuel) and is only left with having to store vitrified fission products in universal canisters (UC-V) and compressed wastes in similar universal canisters (UC-C) as show in Figure 1. In this approach, fresh MOX fuel (which was first loaded in 2014) is added to the reactor along with enriched UO2 fuel produced from natural uranium (ENU) and re-enriched reprocessed uranium (ERepU). At the end of each operating cycle, some used ENU, ERepU, and MOX fuels are removed from the reactor and sent to La Hague for reprocessing.

The reprocessing of these different fuels at La Hague require careful assessment to respect the safety parameters of the plant. Nonetheless, these fuels can all be reprocessed at La Hague essentially through a dilution process of the used MOX fuel with used ENU. This is necessary to ensure the degraded Pu-isotope vector from the used MOX fuel (buildup of even Pu isotopes) is mixed with the better Pu-isotope vector from the used ENU.

Fig. 1. Resulting Wastes from Reprocessing in Universal Canisters Requiring Storage.

In the second approach, not yet implemented at a nuclear plant but being investigated as a potential recycling approach for SMRs deployed outside of the U.S., involves redesigning a fuel assembly to mix ENU rods with MOX rods. As shown in Figure 2, a MOX-2 fuel assembly contains a pattern (still to be optimized) of fresh ENU rods mixed with fresh MOX rods. Once this MOX-2 fuel assembly has completed its irradiation cycles in the core of a nuclear reactor, this used MOX-2 fuel will be sent to La Hague for reprocessing. The mixing of ENU and MOX rods allows for this fuel assembly to be recycled with minimum dilution by other used ENU fuel assemblies, as an acceptable Pu-vector can be produced from the recycling of the used ENU rods with heir good Pu-vector and the used MOX rods with their degraded Pu-vector (buildup of even Pu isotopes).

A scheme similar to the one applied by the Borssele NPS can be applied where Orano lends the first core load of plutonium, recycles all the UNF, and at the end of the operation of the reactor receives the final Pu from the final core to balance the initial loan. Figure 3 provides an overview of how this recycling scheme could function with the "loan" for the first cycle and the repayment of the "loan" with the final core off-load (noting: "Orano" in this figure represents the recycling at La Hague and "Client" represents the SMR or LWR).

Fig. 2. Contrasting Traditional ENU and MOX Fuel Assembly Designs with the MOX-2 Design Mixing ENU and MOX Rods.

Fig. 3. Proposed MOX-2 Recycling Scheme.


To date, approximately 400 MT of used fuel has been recycled from the Borssele NPS. The reactor runs with a core consisting of ENU, ERepU, and MOX fuels, which will be recycled at the La Hague plant at the end of their period of performance in the core. The COVRA HABOG waste facility (see Figure 4) has been designed and built in 2003 to hold all the high level waste produced (stored in a total of 900 UC-Vs and UC-Cs) from the recycling of the fuel used over the lifetime of the Borssele NPS. This facility is about the size of a small stadium, will contain waste forms suitable for disposal in a repository, and will not contain material requiring IAEA safeguards, thereby simplifying the safety basis of the repository (e.g., no concern for a criticality event).

In addition to the Borssele NPS approach to recycling, Orano is also investigating the benefits of the MOX-2 recycling scheme. This scheme allows for no net fissile plutonium creation as the plutonium would be destroyed at the same rate it is created. Furthermore, the MOX fuel can be used as an alternative to the currently difficult to procure high assay low enriched uranium (HALEU).

There are drawbacks associated with the use and reuse of MOX fuel and they include, but are not limited to: having to design and license the reactor to utilize MOX fuel; in the U.S., MOX requires Category I physical protection features (HALEU is Category II and LEU is Category III per 10 CFR 73); need to design for receipt of equipment containing fresh MOX fuel (MX6 transport cask); enriched boron (instead of natural boron) may be needed for shutdown reactivity margin; more control rods may be necessary (depending on MOX loading); MOX needs longer cooling times in used fuel pools prior to shipment; and used MOX will need to be shipped in specifically designed transportation casks (TN17MAX).

Fig. 4. COVRA HABOG Facility for HLW Storage for Borssele NPS (time lapse from today upper left to +100 years bottom right).


In the end, the benefits of adopting these potential recycling schemes include: reducing or eliminating the net creation of plutonium produced in used fuels while also degrading the plutonium isotope vector (buildup of even isotopes of plutonium); no used fuel left at reactor site (e.g., no issues with chloride induced stress corrosion cracking of welded canisters with SNF); production of a standardized waste form suitable for disposal (simplifying handling and design of disposal facility); reducing uncertainties and risks associated with interim storage and disposal of SNF/HLW (e.g., no criticality concerns); reduces waste volumes requiring disposal; improves security of fuel supply by providing an alternative source of fuel; saves natural uranium and the need for enrichment; and positive social impact.

Finally, what about the costs of these schemes? The Borssele NPS has found the costs are comparable to the once through fuel cycle, while reducing the uncertainty and risk for an as-yet designated or designed disposal facility. This result is consistent with the findings of a 2013 OECD NEA report [2], which compared the direct disposal and one-time recycling with MOX schemes and found the costs of recycling is offset by the savings in NU and disposal costs. As shown in Figure 5 (Figure 3.23 from [2]), the direct disposal route cumulative costs are similar to those associated with the partial recycling in LWR strategy. Hence, the proposed multi-recycling scheme enabled to recycle all fuel types would likely significantly reduce the uncertainty associated with the partial-recycling strategy.

In summary, Orano continues to perform R&D that improves UNF management, while challenging the existing paradigms of UNF management and associated hesitancy towards recycling.

Fig. 5. Fuel Cycle Cost Breakdown for Different Strategies (Assumed Capacity of 25 TWh/yr and 0% Discount Rate) [2].


  1. IAEA (2022), Country Nuclear Power Profiles, The Netherlands (see 2.7.3. Reprocessing)

  2. NEA (2013), The Economics of the Back End of the Nuclear Fuel Cycle, OECD Publishing, Paris.


Presentation: Re-Use of Used MOX LWR Fuel (ANS Meeting, 2023-0613)

Orano: The world leader in recycling used nuclear fuels (process videos and animations)

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