Comprehensive studies for the qualification of an industrial process for PuCl3 synthesis – NIOUSALT

The purity of the salt at each stage of preparation—chlorination, mixing, and final liquid-phase purification—as well as the compatibility of structural materials with the various reaction media, are critical factors that must be defined for process qualification. By leveraging Orano’s expertise alongside that of two leading laboratories, UCCS (Chemistry) and UMET (Materials), the chair is conducting the necessary experiments to identify and parameterize a PuCl3 synthesis route. This route must be compatible with Orano’s existing industrial fuel reprocessing process at La Hague and scalable to industrial levels. The chosen approach is the synthesis of PuCl3 via a gas-solid reaction, using a chemical form that aligns with current production methods. Since plutonium handling is restricted to authorized personnel in dedicated facilities, experimental data are obtained using non-radioactive surrogates such as cerium or neodymium. The work program is structured around six workpackages, progressing from bench-scale synthesis to semi-pilot scale. It includes the study of materials and interfacial interactions.

A chlorination bench has been designed and installed at UCCS. A series of solid-gas reaction syntheses successfully produced cerium chloride with very high conversion yields (>95%). A parametric study was conducted to assess the impact of heating rate, operating temperature, holding time, gas flow rate, and hydrogen/HCl content on the final powder composition. This campaign shed light on the reaction mechanisms underlying CeCl3 formation and guided the parameterization of full-scale trials at Orano’s Center for Innovation in Extractive Metallurgy. Purification of CeCl3 in molten chloride salts, as well as other innovative synthesis routes for CeCl3 and UCl3, are currently under investigation. In parallel, a state-of-the-art review of materials enabled the selection of several candidates. Their microstructure (hardness, grain size, phase) was analyzed to qualify the microstructure prior to high-temperature molten salt immersion tests. A dedicated setup for corrosion testing in controlled-chemistry, high-temperature molten chloride salts has been designed, fabricated, and validated at UMET. For cost reasons, the NaCl-LaCl3 salt system will first be used to validate the experimental protocol and identify initial damage mechanisms before transferring the tests to the NaCl-CeCl3 system. To deepen the understanding of interfacial reaction mechanisms, structural determination of potential phases has been initiated in systems combining salt elements and metallic elements from alloys. The selected crystal growth methods include Chemical Vapor Transport (CVT) and Molten Salt Synthesis (MSS) in order to mimic the operating conditions of synthesis and purification reactors and to simulate the metal alloy/gas vector and metal alloy/molten bath interfaces, respectively.

Various impurities—including oxides, oxychlorides, and reaction intermediates—have been identified during solid-gas chlorination. The next phase of testing aims to define operating conditions that either prevent their formation or, where necessary, chlorinate them for removal. The parametric study of the solid-gas reaction will be extended to other precursors of interest to Orano.
Since the produced salt is intended for use in mixtures with other components, an in-depth study of purification in molten salt baths will also be conducted. Special attention will be given to understanding scale effects and corrosion mechanisms, leveraging synergies with future test campaigns planned at Orano’s Center for Innovation in Extractive Metallurgy. To this end, samples, dust, and visual inspections of equipment will be analyzed after the next campaign.
This program will be accompanied by enhanced collaboration within the chair, focusing on the study of material reactivity at interfaces through (i) the assessment of material performance under high-temperature exposure to chlorinated gas atmospheres and (ii) the structural determination of phases likely to form through reactions between metal alloys and carrier gases and/or the molten bath.

To date, the chair’s research has been presented in two national conferences (R3C 2024, CENTRA 2025) and one international conference (NUFUEL 2025). Additionally, a technical brief detailing an original method for UCl3 synthesis has been prepared, with the aim of initiating a patentability study.

The ambition of the NIOUSALT Industrial Chair is to take part of the French national challenge for a more sustainable, safer and more economical nuclear power, as targeted in the objectives of the France 2030 program and in the sustainable development objectives adopted by the United Nations.

The NIOUSALT Industrial Chair is built on a strong and long-standing partnership between the French laboratory UCCS (Unit for Catalysis and Solid Chemistry UMR 8181) and the French company ORANO. In partnership with Lille University and Polytech'Lille, based in Villeneuve d'Ascq (north of France), the chair aims to develop a new research collaboration on Molten Salt Reactors (MSR) for the nuclear industry.

The chair is supported and coordinated by Professor Murielle Rivenet who leads the CIMEND team (Chemistry, Materials and Processes for Sustainable Nuclear) of the UCCS laboratory whose research focuses on lanthanides and actinides chemistry for the nuclear fuel cycle with the aim to recover valuable materials or to re-use by-products.

The scientific program of NIOUSALT aims to parameterize the full-scale synthesis of a fuel modelling PuCl3 by using a route which is compatible with the current recycling processes of used nuclear fuel. One of the main deliverables of the project is to provide the optimal synthesis conditions allowing, by 2030, to develop a pilot salt production facility able to produce the quantities of PuCl3 which will be necessary to operate the MSR demonstrators using molten chloride salts.

The program is built on 6 workpackages (WP) considering the experimental syntheses at different scales from laboratory to semi-pilot, each being managed by a leader. It will involve the recruitment of 4 trainees, 4 doctoral students, 4 engineers and 1 graduate assistant and includes the creation of a Specialized Master.

The chair has set up a governance based on 4 regular committees to manage: i) monitoring of scientific advances with COTECH (4/year), ii) monitoring of orientations within the framework of a COS (2/year), iii) reports, monitoring of deliverables and indicators, operational decisions, dissemination and exploitation of results with the CODIR (1/month) and iv) general management in the presence of the directors, partners and funders with the COPIL (1/year).

Aiming to address major awaited results on the synthesis of PuCl3 surrogates, to train students, to publish and patent the scientific results and to contribute to the development of a semi-pilot, the NIOUSALT Industrial Chair acts a very structuring and strategic project for the partners and for the nuclear industry.