Molten Salt Reactors (MSR)
Molten Salt Reactors (MSRs) are a class of nuclear fission reactors where molten salts serve as the reactor fuel, coolant, and / or moderator. Research on MSRs began early in the development of nuclear energy. These reactors can operate at lower pressures (ambient) and higher temperatures compared to conventional water-cooled reactors.
MSRs cover a wide range of designs, with numerous options being explored, making it challenging to provide a concise overview. Several MSR concepts are currently in development, many featuring small, modular designs at various stages of technological readiness.
Presentation of the Molten Salt Reactor System
Many design variants have been proposed, and the classification of the different MSR variants can be complex. However, there are three main categories based on the role of the molten salts in the reactor:
- Molten salt fuel - pumped
- Molten salt fuel – natural circulation
- Molten salt coolant only
MSRs are a can operate with fast, thermal, or epithermal neutron spectra.
Modern interest in MSRs includes both thermal and fast liquid salt fueled reactor concepts as a long-term alternative to provide large-scale primary energy. Solid-fueled, molten-salt cooled reactors have also been under development for the past couple of decades. Both thermal- and fast- spectrum MSRs are under development by multiple prospective vendors with thermal-spectrum test and commercial reactors anticipated to be deployed this decade and the first fast-spectrum test reactor also anticipated to be deployed this decade.
Some designs feature coupled, on-site fuel salt processing. Fuel salt processing may enable breeding additional fissile material from fertile components of the fuel salt. R&D progresses toward resolving feasibility issues and assessing the safety and performance of the design concepts. Key feasibility issues focus on developing a tailored safety approach and the development of long-life structural and moderator materials. Much work is needed on onsite fuel salt processing and, in general, on molten salt technology and related equipment.
Benefits and Applications of MSR (Opportunities)
Higher Temperatures, Lower Pressures
- High-Temperature Operation: MSRs operate at higher temperatures (typically above 600°C) compared to traditional water-cooled reactors. This results in higher thermal efficiency electricity generation and more efficient coupling to non-electrical applications.
- Versatile Heat Applications: The high-temperature heat produced by MSRs could be used for various industrial applications beyond electricity generation, such as hydrogen production, water desalination, and process heat for chemical industries.
- Low Pressure Operation: MSRs operate at atmospheric or low pressures, significantly reducing the risk of pressure-related accidents and explosions compared to high-pressure water reactors.
- Passive safety features: Many MSR-fueled designs incorporate passive safety features, such as passive cooling and the potential for defueling in response to accidents which enhance the reactor's safety profile without requiring active intervention.
More Efficient Fuel Utilization
- Higher Burnup Rates: Molten salt fuels are less limited than conventional solid fuels by burnup constraints, enabling higher fuel utilization and reducing the frequency of refueling.
- Flexible Fuel Cycle: Molten salt fueled reactors can incorporate uranium, plutonium or a mixture of both as fissile inventories. This flexibility allows for the use of plutonium inventories when they exist. Thorium fuel cycles have also been proposed for MSRs, which would require an initial fissile inventory of either U or Pu.
- Lower Waste Volume: The efficient use of fuel and higher burnup rates in MSRs can lead to a reduction in the volume of nuclear waste produced.
- Potential for closing the fuel cycle, in MSR-fueled designs, if processing and continuous recycling of the fuel is implemented
Main Challenges for the Deployment of MSR
Materials Challenges
MSRs operate at high temperatures and with molten salts for which corrosion can an issue. Finding materials that can withstand this harsh chemical environment, resist corrosion, endure high temperatures, and tolerate neutron fluxes over long periods remains a significant challenge.
Addressing these materials challenges requires extensive research and development. This includes testing and qualifying new alloys, composites, and coatings that can meet the demanding conditions of MSR operation.
Monitoring and Chemistry Control of Molten Salts, with potential Online Purification
Fuel Salt Processing: The online processing of liquid fuel salts to extract fission products and manage the chemistry of the salt mixture is one of the most promising aspects of MSRs. However, this area needs further investigation and demonstration to ensure reliability and efficiency.
Safety Demonstration and Regulation
Novel Designs and Fuel Cycles: MSRs employ innovative designs and fuel cycles, necessitating thorough safety demonstrations and regulatory approval. Developing safety cases and regulatory frameworks for MSRs is a key condition for its success.
Scale-up and Commercialisation
Scaling Up Technology: Transitioning from experimental or small-scale models to full-scale commercial reactors involves significant challenges in scaling up the technology and demonstrating its economic viability at a commercial level.
How is GIF working to solve those
GIF has established, since 2010, a provisional MSR System Steering Committee (MSR pSSC). The MSR pSSC is an initial framework to allow cooperation between GIF member countries interested in advancing MSR R&D and to identify areas of future collaboration. Participating countries and their years of joining are summarized in the page of the MSR pSSC that you can access by following the link below.
MSR Projects History - Past projects
From the 1950s through the 1970s, a significant MSR development programme was conducted in the United States. Two test reactors were successfully operated: the Aircraft Reactor Experiment (ARE) and the Molten Salt Reactor Experiment (MSRE). A preliminary design of a 1,000 MWe reactor, the Molten Salt Breeder Reactor (MSBR) based on the thorium-uranium-233 fuel cycle, was completed, and a design was partially developed for a demonstration reactor. These programmes laid the foundation for thermal neutron MSR technology.
While the concept of a fluoride salt-cooled high-temperature reactor (FHR) originated in the 1970s with the advent of TRISO fuel, significant development of FHR, which only use molten salts as their coolant, resumed twenty years ago. Other countries, including the UK and the Soviet Union, also initiated MSR-related research programmes during this period.
Project/Program | Country | Power Rating | Timeframe | Notes |
|---|---|---|---|---|
| Aircraft Reactor Experiment | US | 2.5 MWe | 1950s | Demonstrated by HTRE (High Temperature Reactor Experiments) |
| Molten-Salt Reactor Experiment (MSRE) | Oak Ridge National Laboratory, US | 7.4 MWth | 1960s | Critical in 1965, operated for 4 years |
| Molten Salt Fast Reactor (MSFR) | Atomic Energy Research Establishment, UK | 1500 MWe 3000 MWth | 1964-1973 | Cooperation with Oak Ridge, US |
| Molten Salt Breeder Reactor (MSBR) | Oak Ridge National Laboratory, US | 10 MWth | 1970–1976 | Fuel: LiF/BeF2/ThF4/UF4 with graphite moderator |
| Molten-salt reactor Research Program | Kurchatov Institute, Soviet Union | N/A | 1970s | Concluded that no physical nor technological obstacles prevented the practical implementation of MSR. |
| Denatured molten salt reactor | Oak Ridge National Laboratory, US | 8 MWth | 1980s | Never Built |
GIF MSR Related Publications
GIF has produced several reports and conducted analysis on MSR Systems produced by cross cutting methodological working groups (Risk and Safety WG, Proliferation Resistance & Physical Protection Working Group). GIF's annual reports, technology roadmap and R&D Outlooks provide more information on the progress made by GIF's MSR provisional System Steering Committee and Project Management Boards.
