Molten salts are broadly used in industry, even though its corrosion is an important consideration that often limits the full potential of a technology.

In renewable Energy sector, in solar energy applications, particularly concentrated solar power (CSP) systems, molten salts are used as heat transfer fluids and thermal energy storage materials. Understanding and mitigating corrosion is crucial to ensure the longevity and efficiency of these systems, as corrosion can lead to system failures, leaks, and increased maintenance costs.

In Chemical Industry, molten salts are often used in various high-temperature processes, such as in the production of metals and other industrial chemicals. Corrosion resistance is vital for equipment durability and safety in these environments, where aggressive chemical reactions can occur. Proper management of corrosion can enhance productivity and reduce operational costs.

In Nuclear Industry, in nuclear reactors, particularly in advanced designs such as molten salt reactors (MSRs), molten salts can serve as both a coolant and fuel medium. The corrosion behavior of materials in contact with molten salts at high temperatures is critical for the safety, efficiency, and reliability of nuclear systems. Understanding corrosion mechanisms can lead to the development of more robust materials that improve the lifespan and performance of reactors.

Overall, addressing molten salt corrosion is essential for the stability, safety, and economic viability of technologies and systems across these industries. Research and development in this area aim to improve materials used in these applications to resist corrosion, thereby enabling safer and more efficient operations.

Research at CIC energiGUNE

At CIC energiGUNE, the research group Interfacial Phenomena and Porous Media has a rich experience in molten salts corrosion, particularly in the realm of Concentrated Solar Power (CSP) technologies studying corrosion of nitrate and carbonate molten salts and corresponding anti-corrosion measures. Currently, among others, CIC energiGUNE collaborates with Fraunhofer Institute for Solar Energy Systems (ISE) testing at large-scale such corrosion mitigation strategies as Graphitization, Laser texturing and Nanomaterials-based coatings and with the University of the Basque country on the corrosion of molten chlorides.

^{Scanning electron microscope images of Stainless steel 310 after corrosion test with molten carbonate salt: left, non-protected case and right, protected with graphitization method developed at CIC energiGUNE}

Recently global and European interest in Molten Salt Nuclear Reactors (MSRs) is evident due to several important advantages of this technology:

• Enhanced Safety: MSRs operate at atmospheric pressure, which significantly reduces the risk of catastrophic failures associated with high-pressure systems. Additionally, their design allows for passive safety features, such as the ability to drain the molten salt into safe storage tanks in case of overheating or other emergencies.
• Efficient Fuel Utilization: MSRs can utilize a variety of fuels, including uranium, thorium, and even spent nuclear fuel. This flexibility allows for more efficient fuel use and the potential for a closed fuel cycle, reducing nuclear waste and making use of materials that would otherwise be considered waste.
• High Operating Temperatures: The ability of molten salts to operate at high temperatures enables higher thermal efficiencies for electricity generation compared to traditional reactors. Higher efficiencies mean more energy can be extracted from the same amount of fuel, enhancing the overall energy output.
• Liquid Fuel Advantages: MSRs use liquid molten salt as both a coolant and fuel carrier, which enhances heat transfer and allows for effective fission reactions. This liquid state also facilitates continuous online refueling and the removal of fission products, leading to better fuel management.
• Low Carbon Emissions: As a form of nuclear energy, MSRs produce minimal greenhouse gas emissions during operation, making them a cleaner alternative to fossil fuels. They can play a significant role in reducing emissions and addressing climate change.
• Waste Management: MSRs can help manage nuclear waste better than traditional reactors. By using fuels like thorium and being designed to significantly reduce the lifespan and toxicity of nuclear waste, MSRs can contribute to more sustainable waste management solutions.
• Compatibility with Renewable Energy: MSRs can complement renewable energy sources by providing a stable baseload supply of electricity. This can help balance the intermittent nature of renewables like solar and wind, leading to more reliable energy systems.
• Research and Development Potential: There is significant ongoing research into the development and optimization of MSRs, which can drive technological advancements and innovations in nuclear power. This research can lead to safer, more efficient, and more versatile reactor designs.

Corrosion is critically important for molten salt nuclear reactors (MSRs) for several reasons:

1. Material Integrity: MSRs operate at high temperatures and involve aggressive chemical environments. The materials used in reactor components, such as piping, pumps, and reactor vessels, must resist corrosion to maintain structural integrity over long operating periods. The failure of these materials due to corrosion could lead to catastrophic breakdowns or leaks.
2. Safety Concerns: Corrosion can lead to the release of radioactive materials into the environment. Ensuring that the materials used in MSRs are resistant to corrosion is vital for the safe containment of radioactive substances and the protection of both the environment and human health.
3. Operational Efficiency: Corrosion can reduce the efficiency of heat transfer and fluid flow within the reactor. If corrosion leads to the degradation of heat exchange surfaces or blockages in piping, it can result in reduced reactor performance and increased operational costs.
4. Longevity and Maintenance: MSRs are designed for long operational lifespans. Understanding and mitigating corrosion is essential for reducing maintenance needs and extending the life of reactor components. Frequent maintenance can lead to operational downtime, affecting the economic viability of the reactor.
5. Choice of Materials: The development of advanced materials that can withstand the specific corrosive environments found in MSRs is crucial. Research into corrosion mechanisms helps guide the selection and engineering of suitable materials, ensuring that they can endure the harsh conditions over extended periods.
6. Regulatory Compliance: Nuclear reactors are subject to stringent regulatory standards to ensure safety and reliability. Effective management of corrosion is necessary to meet these regulations and maintain public trust in nuclear energy.

^{Corrosion investigations of CIC energiGUNE at different scales}

In view of the mentioned above interest and challenges, CIC energiGUNE currently apply its broad experience in molten salts corrosion in the field of MSRs collaborating with industrial and academic partners. We are open to broadening such collaboration performing corrosion tests at different scales and environments (static-dynamic, isothermal – temperature cycling, free corrosion – controlled environment), as well as applying the state-of-the-art material characterization techniques to develop new or improve existing anti-corrosion methods. If you are interested in collaborating with us, do not hesitate to contact us.