Molten salt reactors (MSRs) may play a key role in future nuclear energy systems by offering major advantages in safety and efficiency. Advanced research, technology development and licensing in several countries can potentially make near-term deployment of this innovative technology possible.
The IAEA, which supports the development and deployment of nuclear power technology, will host a webinar on 27 August on Molten Salt Reactors: A Game Changer in the Nuclear Industry. MSRs and their unique advantages in addressing the challenges of the clean energy transition will also be discussed at the annual IAEA Scientific Forum on 22-23 September, during the 64th IAEA General Conference.
MSRs operate on the same basic principle as current nuclear power reactors-controlled fission to produce steam that powers electricity-generating turbines. But they have a fundamental difference: molten salts play a key role in the reactor core, including as a coolant instead of water as used by most currently operating reactors. And instead of fuel rods, most MSR designs involve nuclear fuel dissolved in the coolant.
These features provide benefits including significantly enhanced efficiency, load following, and the ability to operate at high temperatures, which makes them suitable for non-electric applications requiring high heat input.
"Bolstered efficiency and passive safety characteristics are crucial for ensuring the sustainability of nuclear power, and MSRs fit the bill in both areas," said Gerardo Martinez-Guridi, an IAEA nuclear engineer. "Many MSRs using liquid fuel can automatically shut down if their temperature becomes too high, as they are designed to rapidly reduce power in case they begin generating too much heat. This feature makes MSRs ideal for meeting dynamic electricity demand by allowing for quick output adjustments." Some MSRs may also be used to burn spent nuclear fuel (SNF) from current power reactors, reducing the amount of radioactive waste that must be stored, he added.
The MSR concept is not new. Oak Ridge National Laboratory (ORNL) in the United States operated an experimental 7.34 MW (th) MSR from 1965 to 1969, in a trial known as the Molten-Salt Reactor Experiment (MSRE). This demonstrated the feasibility of liquid-fuelled reactors cooled by molten salts and helped identify and later resolve issues such as the need for liquid-liquid chemical extraction methods for molten salt fuel processing.
While work on MSRs has continued in several countries over the last few decades, commercial deployments have remained out of reach. This has been due to a range of issues including regulatory challenges such as the lack of MSR licensing standards as well as supply chain difficulties in sourcing specialized components.
Now, several MSR designs are nearing deployment readiness. These include the ThorCon reactor, a scaled-up version of the MSRE under development in the US, and China's thorium-based MSRs. The latter utilize fuel which is a mix of thorium and uranium, with the purpose of breeding fissile uranium-233 from the thorium in the reactor core. This transmuted uranium-233 is then burned up as fuel.
Denmark is developing two concepts of MSRs, including a small and modular MSR, the Compact Molten Salt Reactor, which is going through the licensing process. And in Canada, the Stable Salt Reactor Wasteburner (SSR-W300) is under design review. The SSR-W300, fuelled with reactor grade plutonium recycled from SNF stocks, has the potential to greatly reduce the burden associated with storing SNF, some of which remains radioactive for thousands of years.
IAEA support
The IAEA supports the development of MSRs through a variety of knowledge exchange initiatives, including a virtual consultancy meeting held last month attended by 21 experts from 13 countries. They worked on drafting an IAEA publication on the status of MSR technology including R&D activities and deployment challenges as well as a taxonomy for classifying the main types of MSRs. The publication is expected out in 2021. There are currently 10 MSR designs in the small modular reactor (SMR) category included in an IAEA publication to be published in September as a supplement to the IAEA's Advanced Reactors Information System (ARIS) database.
The upcoming webinar on MSRs, part of the Webinar Series on Nuclear Technology Breakthroughs for the 21st Century, will feature speakers from organizations in France and the United States involved in developing the technology.
"US MSR development activities include a broad range of cooperative private industry and government activities ranging from basic science, technology development and regulatory framework definition," said David Holcomb, distinguished member of the technical staff at ORNL, who participated in the consultancy meeting and will speak at the webinar. "These activities include developing modelling tools for radionuclide tracking at MSR plants and measuring the thermophysical and thermochemical properties of fuel salts."
The US Nuclear Regulatory Commission is seeking to develop an effective licensing process for MSRs, and multiple US-based, private sector MSR developers have indicated their intention to deploy MSRs within the next decade, he added.
In France, studies are under way to confirm the feasibility of a fast neutron MRS concept, with potential deployment in the next 10 to 20 years, said Elsa Merle, a professor at France's Grenoble Institute of Technology who also took part in the consultancy meeting and will speak at the webinar.
"Utilizing a liquid fuel/coolant mixture in MSRs helps support the intrinsic stability of the reactor core, which allows for easy operation at reduced power while ensuring that safety is maintained," Merle said. "Such reactors may support electricity grid balancing, which is essential to support the rising share of renewable energies."
MSRs are one of six reactor technologies selected by the Generation IV Forum (GIF), an initiative involving 13 countries focused on next generation nuclear power technologies, for further R&D. At an annual meeting in July, the IAEA and GIF called for greater efforts to support the early deployment of innovative reactor systems to address climate change.
MSRs and other advanced and innovative reactors will be featured topics at next month's Scientific Forum, which will focus on how nuclear power's science-based solutions can help drive the transition to clean energy systems.
