MultI-recycling strategies of LWR SNF focusing on MOlten SAlt technology
Horizon Europe
Approval no 101061142
Start: 2022
End: 2026

The MIMOSA project is a European HORIZON-Euratom project started in 2022 and selected on call for projects NRT-01-03 Multi-recycling of spent fuel from Light Water Reactors (LWR). It is coordinated by ORANO with partners such as the SUBATECH laboratory under the triple supervision of the Institut Mines-Télécom through its school, IMT Atlantique, Nantes University and the CNRS with the National Institute of Nuclear Physics and Particle Physics (IN2P3) as the main institute. The project will last 4 years and the EU funding is about 6.9 Millions of euros. The MIMOSA project will devise and demonstrate an integrated multi-recycling strategy of plutonium and uranium combining multi- recycling options in LWRs with recycling Pu and other transuranics today considered as waste in Chloride Molten Salt Reactors.

Project background

In a time of heightened environmental concerns and resource scarcity, the closure of the fuel cycle, which reduces the radioactive waste disposal footprint and the need for natural resources, reinforces a sustainable nuclear energy strategy. This involves reprocessing of spent nuclear fuels (SNFs) and the extraction of elements that can be (re)used. While the EU has the highest share of SNFs reprocessing worldwide, driven by the closed fuel cycle policy in France, most of the spent uranium oxide (UOX) fuels are declared waste today.

The multi-recycling of plutonium is the prime path to achieving nuclear energy’s full potential and multi-recycling in light-water reactors (LWRs) is already under investigation in France. Multi-recycling in light-water reactors (LWRs) is a tangible solution, but it presents some limitations related to the degradation of the plutonium (Pu) isotopic composition and the generation of minor actinides (MAs). Significant improvement in converting Pu isotopes and MA into fission products with shorter half-lives can be achieved with the introduction of advanced fast reactor systems, among which the molten salt reactor using Chloride salt (Cl MSRs) is a particularly promising option.

Project objective and relevance

MIMOSA aims to develop an accessible, cost/risk optimised multi-recycling strategy of Light Water Reactors (LWR) spent fuels, based primarily on multi-recycling of Pu and Reprocessed Uranium in LWRs combined with the Chloride Molten Salt Reactors, and using already available infrastructure in the EU such as the French reprocessing plant, not only for its existing LWR fuel treatment capabilities, but also for its Pu partitioning and waste conditioning capabilities, its compatibility with chloride salts, and in the future, for its potential additional capabilities in MA separation and salt management.

This strategy will also be compared with other multi-recycling scenarios. MIMOSA focus more specifically on the demonstration of several key aspects of technical feasibility and performance of Cl MSRs, that will contribute to accelerating the deployment of this advanced technology, on Pu and Minor Actinide conversion respectively and on production of valuable isotopes for other applications.


In the proposed model, Cl MSRs will be used to fission Pu with low fissile content and MA from multi-recycled fuel originating from LWR and/or LWR+FR fleets. The associated fuel salt will be fabricated and recycled in a reprocessing plant like Orano’s La Hague plant, used in addition to its existing LWR fuel treatment capabilities (including used MOX fuel), for its Pu partitioning and waste conditioning capabilities and its compatibility with chloride salts. The functionality may be completed in the future with a MA or Pu+MA advanced separation step, see Figure 1.



Fig 1 : MIMOSA overall concept


Today, the maturity of Chloride Molten Salt Reactors is low. For this reason, the MIMOSA consortium will also seek to demonstrate several key aspects of technical feasibility and performance :

  • Development of synthesis routes of the chloride fuel salt for use at the industrial scale
  • Selection and qualification of optimized fuel salt composition with respect to thermo-physical properties
  • Qualification of innovative materials, new corrosion monitoring and mitigation methods, control of accidental situation
  • Pyro-chemical processes to recycle Pu and AM
  • New methods for fission product management: removal, disposal, extraction and purification when valuable
  • Qualification of codes coupling neutronics and thermo-hydraulics

Role of the school and IMT partner schools

Subatech is involved in the Work Package 3 dedicated to simulations of chloride molten salt composition evolution in the reactor to support fuel cycle calculations, safety evaluation and the analysis of valuable isotopes. WP3 will assess the behaviour of Cl MSRs with regards to molten salt composition evolution, neutronic and thermohydraulics.

Behaviour and expected outcomes based on this behaviour : performance of MSRs in terms of Pu and minor actinide conversion (WP1), spent fuel salt to be managed (WP5), production of valuable isotopes (WP6), impact on reactor safety, radioprotection and key aspects of operation.

The expected outcomes are the following :

  • Isotopic vectors of spent fuel salt,
  • Neutronic properties of Cl salts in comparison with Fluoride salts,
  • Decay heat and radiation fields produced by spent fuel salt
  • Comparison of three different simulation approaches to assessing the impact of varying delayed neutron fraction and the presence of non-critical regions to reactor safety.

Subatech is task leader of the task T3.1 on Isotopic evolution of the fuel salt for reference MSR designs (Partners: CNRS, IMT Atlantique, Grenoble INP, Orano, Thorizon, EDF).

French and foreign academic and industrial participants/partners

  • ORANO SUPPORT, France (Coordinator)
  • THORIZON HOLDING BV,  Netherlands
  • LISTO BVBA, Belgium
  • ARTTIC, France
  • ELECTRICITE DE France, France

Third party Institutes



The CNRS coordinates the project for the 3 involved CNRS/IN2P3 laboratories: LPSC, IJCLAB, SUBATECH (Triple supervisors: CNRS-IN2P3, IMT Atlantique, University of Nantes) with for SUBATECH an associate professor of IMT Atlantique in charge locally of the MIMOSA project and of Task leader (T3.1).

Expected results

Subatech is task leader of the task T3.1 on Isotopic evolution of the fuel salt for reference MSR designs (Partners: CNRS, IMT Atlantique, Grenoble INP, Orano, Thorizon, EDF).

Delivrable over the 30th month project for Subatech

D3.1: Isotopic composition evolutions, decay heat and dose rate evaluations

Financing requirements


Call : NRT-01-03: Multi-recycling of spent nuclear fuel from light water reactors (LWR)

Project : 101061142

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Logo Europe  This project has received funding from the Horizon Europe Framework Programme (2021-2027) under grant agreement no. 101120779

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