From Batch to Continuous: The MSR Fuel Processing Paradigm Shift
Molten salt reactor fuel processing diverges fundamentally from conventional solid-fuel reprocessing because the fuel salt is liquid — enabling continuous or semi-continuous processing directly coupled to reactor operation. This is a paradigm shift from the batch-mode PUREX aqueous reprocessing used in light water reactor (LWR) fleets, and it is the central engineering opportunity — and challenge — driving the current wave of patent activity.
The technology spans four interconnected domains: fuel salt formulation and preparation; online composition monitoring and adjustment; salt clean-up and pyrochemical reprocessing; and spent fuel conversion into MSR fuel feed. Foundational experimental work at Oak Ridge National Laboratory (ORNL) established continuous reprocessing of fluoride molten salts as early as 1965–1966. Contemporary filings now extend this concept to chloride fast-spectrum systems, thorium-uranium breeders, and integrated waste-burning configurations.
MSR fuel processing encompasses the preparation, online management, reprocessing, and recycling of liquid halide fuel salts that serve simultaneously as fuel carrier and heat transfer medium in Generation IV nuclear systems. Because the fuel is liquid, processing can occur continuously during reactor operation — eliminating the cooling, fabrication, and transport delays inherent in solid fuel cycles.
This report surveys the patent and literature landscape covering core processing mechanisms, fuel salt formulations, online composition control, and waste management strategies. The dataset represents a snapshot of innovation signals and should not be interpreted as a comprehensive view of the full industry.
Molten salt reactor fuel processing enables continuous or semi-continuous reprocessing directly coupled to reactor operation, a fundamental departure from the batch-mode PUREX aqueous reprocessing used in light water reactor fleets.
Six Decades of Innovation: From ORNL to Commercial Filings
The MSR fuel processing patent record stretches from a 1966 US Atomic Energy Commission filing to a 2025 European patent — a span that reflects two distinct eras: an ORNL-driven foundational period and a private-sector commercialization surge beginning around 2014.
The foundational era (pre-2000) produced just two patents in this dataset: a 1966 US Atomic Energy Commission filing establishing continuous fluoride salt reprocessing, and a 1970 Australian patent addressing fuel cycle economics for single-fluid molten salt breeder reactors. Both reflect the ORNL Molten Salt Breeder Reactor program.
The re-emergence period (2006–2015) was primarily academic. The thorium MSR re-evaluation by Laboratoire de Physique Subatomique et de Cosmologie (LPSC) in 2006 identified reprocessing complexity as a key challenge. By 2012, CRIEPI’s review of pyroprocessing fuel cycle technology and Nuclear Research Institute Rez’s work on pyrochemical reprocessing and fluoride volatility methods signaled growing institutional readiness for closed fuel cycles. CRIEPI’s analysis established engineering-scale feasibility at 40 tonHM/y throughput — a figure that remains a benchmark for process design.
The private-sector entry and patenting surge (2014–2021) marks the decisive shift. Terrestrial Energy filed its first Integral Molten Salt Reactor patents in Israel in 2014, followed by EP and HU registrations in 2018. TerraPower filed chloride fuel salt claims in EP in 2021. Copenhagen Atomics secured EP protection for laser-based real-time salt composition diagnostics in 2020. The heaviest filing cluster in this dataset falls between 2018 and 2024.
“The most recent patent in this dataset — Metatomic’s EP 2025 filing — describes an end-to-end chloride fuel-salt preparation process from spent LWR fuel, representing a shift from laboratory-scale demonstrations to licensable manufacturing process claims.”
The commercialization-oriented cohort (2022–2025) introduces the most operationally specific filings: Ian Richard Scott’s 2022 GB patent on electroreduction of spent UO₂ into halide fuel, TerraPower’s 2024 EP extension of chloride fuel salt manufacturing claims, and Metatomic’s 2025 EP patent detailing an eight-step granulation-chlorination process line. These filings mark the transition from concept to licensable process IP.
Map the full MSR fuel processing patent landscape with PatSnap Eureka’s AI-powered search and analysis tools.
Explore MSR Patents in PatSnap Eureka →Four Technology Clusters Defining the Field
MSR fuel processing innovation clusters around four interconnected technical domains. The balance of patent and literature activity across these clusters reveals where IP is concentrated, where academic openness persists, and where processing complexity remains unsolved.
Cluster 1: Fuel Salt Formulation — Fluoride and Chloride Systems
This is the most densely represented cluster in the dataset. Two principal salt families emerge: fluoride salts (FLiBe-based LiF-BeF₂ matrices with ThF₄, UF₄, or PuF₃) suited to thermal-spectrum reactors, and chloride salts (NaCl-UCl₃ or NaCl-KCl-MgCl₂ matrices with actinide trichlorides) suited to fast-spectrum reactors. TerraPower holds the broadest IP position on chloride salt formulations, covering binary, ternary, and quaternary uranium chlorides, UClₓFᵧ mixed halides, and bromide salts, with explicit claims on anti-proliferation composition design across EP (2021, 2024) and BR (2023) filings. Academic literature from Shanghai Institute of Applied Physics (Chinese Academy of Sciences) and University of Liverpool further characterizes NaCl-UCl₃ system breeding performance and salt clean-up sensitivity for fast-spectrum operation.
TerraPower LLC holds the broadest chloride fuel salt formulation IP in the MSR sector, covering binary, ternary, and quaternary uranium chlorides, UClₓFᵧ mixed halides, and bromide salts across EP (2021, 2024) and BR (2023) filings, with explicit anti-proliferation composition design claims.
Cluster 2: Online Salt Monitoring, Composition Control, and Reactivity Management
A critical processing challenge unique to liquid-fueled MSRs is continuous compositional drift due to fission product buildup, actinide transmutation, and oxidation state changes. Two patent-protected approaches address this. Copenhagen Atomics’ EP 2020 patent covers Laser-Induced Breakdown Spectroscopy (LIBS) for real-time diagnostics: a laser beam directed onto the melt or a sample generates plasma, and the emission spectrum is analyzed to determine salt composition and guide reprocessing interventions. Scott’s EP 2018 patent covers sacrificial metal redox control: a sacrificial metal continuously contacting the molten salt maintains the actinide trihalide-to-tetrahalide ratio, preventing both actinide metal precipitation and over-reduction. TerraPower’s EP 2019 patent covers volumetric fuel salt exchange, fluidically exchanging volumes of fuel salt with fertile material/carrier salt mixtures to maintain reactivity within nominal range. Together, these three mechanisms — spectroscopic, electrochemical, and volumetric — define the current IP frontier for closed-loop composition control.
Cluster 3: Pyrochemical Reprocessing and Demand-Driven Salt Clean-Up
Pyrochemical methods — operating in molten salt media at high temperatures — are the leading candidates for online or offline MSR fuel reprocessing, avoiding the aqueous waste streams of PUREX. According to IAEA assessments of advanced fuel cycle technologies, pyrochemical separation offers inherent proliferation resistance advantages over aqueous routes. Nuclear Research Institute Rez described the fluoride volatility method combined with electrochemical separation for both MSR fuel reprocessing and spent LWR fuel preparation. CRIEPI’s 2012 review established engineering-scale feasibility at 40 tonHM/y throughput for closing the actinide cycle.
University of Liverpool’s iMAGINE program produced the most active academic research thread on this topic: a “demand-driven” or “reverse reprocessing” strategy that prioritizes which specific fission product elements to remove based on neutron economy impact, rather than performing full chemical separation. The 2018 priority list publication and the 2022 HELIOS-based dynamic salt clean-up study mark increasing computational maturity for this approach. STFC Daresbury Laboratory further identified key poisoning elements for separation in an integrated MSFR clean-up system in 2022.
University of Liverpool’s iMAGINE framework defines “reverse reprocessing” — removing only the fission product elements that most negatively impact neutron economy, in priority order, rather than performing full chemical separation. This approach reduces processing complexity and proliferation vectors, and represents the most active academic research thread in the dataset with publications from 2018, 2020, 2021, and 2022.
Cluster 4: Spent LWR Fuel Conversion into MSR Fuel Feed
Converting legacy LWR spent fuel into MSR halide fuel is an emerging processing pathway that would simultaneously address spent fuel inventories and provide fissile feed without dedicated enrichment. Two patent-protected routes now exist. Scott’s 2022 GB patent electrochemically reduces spent UO₂ in a halide salt electrolyte above the melting point of uranium metal, forming a U/higher-actinide alloy that agglomerates for subsequent chlorination or fluorination — the key innovation being operation above the uranium melting point to enable agglomeration. Metatomic’s 2025 EP patent is the most operationally detailed process patent in the dataset, sequencing eight steps: (1) fuel pellet removal from assemblies, (2) granulation, (3) chlorination to produce actinide chloride salt, (4) enrichment adjustment, (5) re-chlorination to yield molten chloride fuel, (6) quality certification, (7) pumping/cooling, and (8) milling to specification. Korea Atomic Energy Research Institute (KAERI) demonstrated selective dissolution of transuranic and rare earth elements from UO₂ matrices in LiCl-KCl-UCl₃ molten salt without structural damage to the bulk fuel, published in 2021.
Metatomic Inc.’s EP 2025 patent describes an eight-step process — pellet removal, granulation, chlorination, enrichment adjustment, re-chlorination, quality certification, pumping/cooling, and milling — for converting spent LWR fuel into certified molten chloride MSR fuel, representing the most operationally specific fuel preparation process patent in the field.
Assignee and Jurisdiction Landscape: EP Dominates, North America Leads Commercially
Among active patents in this dataset with clear assignees, the filing landscape is concentrated among a small number of private ventures, with the European Patent Office serving as the near-universal filing jurisdiction for commercially active players.
Terrestrial Energy (Canada) leads by filing breadth with 5 active patents spanning Israel (3 filings: 2014, 2021, 2020), EP (2018), and HU (2018), covering the Integral Molten Salt Reactor core and fuel salt containment concept. TerraPower (USA) holds 3 active patents covering the broadest chloride fuel salt formulation IP. Ian Richard Scott (UK independent inventor) holds 2 active patents covering two distinct processing steps — chemical optimization (EP, 2018) and spent fuel conversion (GB, 2022) — an unusual position for an individual inventor in a capital-intensive field.
Jurisdiction concentration is striking: EP is the near-universal filing jurisdiction for commercially active assignees in this dataset, appearing in filings by TerraPower, Terrestrial Energy, Scott, Seaborg, Copenhagen Atomics, and Metatomic. This reflects the importance of European markets, licensing partners, and the ongoing EU-funded research programs including SAMOFAR and EVOL. According to EPO filing trends in advanced nuclear technology, the European patent system provides broad geographic coverage through a single prosecution, making it the natural first-choice jurisdiction for international MSR ventures.
Academic literature originates from a geographically broader base: UK (University of Liverpool dominant — at least 5 publications; STFC Daresbury; Cambridge), China (Shanghai Institute of Applied Physics, Chinese Academy of Sciences), Korea (KAERI), continental Europe (RWTH Aachen, Paul Scherrer Institut, LPSC Grenoble), and Russia (MEPhI). This broad academic base contrasts with a commercially filing landscape concentrated among North American and European private ventures. As noted by OECD NEA in its assessments of Generation IV fuel cycle readiness, the gap between academic output and commercial IP protection represents both a risk and an opportunity for the sector.
Run freedom-to-operate analysis on TerraPower’s chloride salt claims and identify white space for your MSR program.
Analyse Patents with PatSnap Eureka →Emerging Directions, Strategic Implications, and IP White Space
The most recent filings and publications (2022–2025) in this dataset signal five forward-looking directions that define where the technology and IP landscape is heading — and where accessible filing opportunities remain.
The Chloride Fast-Spectrum Shift
The balance of recent filings (TerraPower chloride salts, Metatomic chloride preparation, Scott chloride conversion) and literature (Shanghai CAS chloride breeding analyses, University of Liverpool chloride clean-up studies) indicates a center-of-gravity shift toward chloride fast reactors, driven by higher actinide solubility and superior breeding performance compared to fluoride thermal systems. Paul Scherrer Institut investigated breed-and-burn fuel cycles in chloride-fueled MSRs without actinide separation in 2019. Chinese Academy of Sciences analyzed thorium-uranium breeding in optimized molten chloride fast reactors using LEU, plutonium, or TRU as startup fissile materials in 2020.
Spent LWR Fuel as a Commercial Feedstock
Two active patents now cover the LWR-spent-fuel-to-MSR-fuel conversion pathway: Scott (GB, 2022) and Metatomic (EP, 2025). This framing — positioning MSR fuel processing as a solution to the existing approximately 400,000-tonne global spent fuel stockpile — is likely to attract regulatory and commercial interest. It reframes MSR fuel processing not as a cost center but as a waste management service with commercial value. Competitors should accelerate IP positioning in this sub-domain given the small number of currently active patents.
Real-Time LIBS Diagnostics for Automated Operations
Copenhagen Atomics’ 2020 patent on laser-based melt composition analysis points toward automated, sensor-driven reprocessing decisions — a necessary capability for unattended or minimally-staffed MSR operations envisioned in small modular configurations. The LIBS approach generates plasma from the melt surface and analyzes the emission spectrum to determine salt composition in real time, enabling closed-loop control of reprocessing interventions without human operator decisions.
IP White Space: Mid-Process Steps Are Largely Unprotected
The patent landscape shows strong coverage at the endpoints — fuel salt formulation (TerraPower) and full process lines (Metatomic) — but limited granted IP on intermediate sub-processes. Specifically, the following areas represent accessible filing opportunities based on the dataset: selective lanthanide/actinide separation within molten chloride media; decontamination of carrier salt for recycle; and off-gas management of volatile fission products including krypton, xenon, and caesium. The UK and EU academic ecosystem (Liverpool, STFC Daresbury, Paul Scherrer Institut) is generating foundational research on demand-driven clean-up without commensurate patent output, creating licensing and partnership opportunities for commercial players seeking validated clean-up process science without the cost of primary research.
IP white space in MSR fuel processing exists in mid-process steps including selective lanthanide/actinide separation within molten chloride media, carrier salt decontamination for recycle, and off-gas management of volatile fission products (krypton, xenon, caesium) — areas with active academic research but limited granted patent protection as of 2025.
Application Domains Beyond Power Generation
The liquid fuel form enables processing applications not available to solid-fuel reactors. University of Tennessee proposed a “sourdough” refueling strategy (2021) whereby excess fuel salt grown during operation seeds new reactor cores, with enrichment level of the refuel salt governing growth rate. University of Liverpool demonstrated weapon-grade plutonium burning in a molten chloride fast reactor as more efficient than alternative reactor types, with integrated process design to reduce security concerns. An Indonesian conceptual design study demonstrated Mo-99 medical isotope production from an Innovative Compact Molten Salt Reactor using NaF-ThF₄-UF₄ fuel — the liquid fuel form enabling continuous extraction of fission products as a co-product stream. RWTH Aachen University showed that MSRs can substantially shorten partitioning and transmutation timescales by eliminating cooling and fabrication delays inherent in solid fuel cycles.