Molten salt reactors (MSRs) use molten fluoride salts as primary coolant, at low pressure. They may operate with epithermal or fast neutron spectrums, and with a variety of fuels. Much of the interest today in reviving the MSR concept relates to using thorium (to breed fissile uranium-233), where an initial source of fissile material such as plutonium-239 needs to be provided. MSRs offer enhanced safety, efficient fuel use and the potential to reduce long-lived radioactive waste. However, a central challenge for MSRs is ensuring that structural materials can withstand hot, corrosive salt and radiation for many years.
Thorizon addresses this challenge through its cartridge design. The fuel salt is contained in sealed cartridges that are replaced after five to ten years, limiting the exposure of key components to the salt and enabling their inspection and replacement during scheduled cartridge changes. The design provides a practical way to manage material degradation, but it must be supported by evidence. Regulators and operators need to know how materials behave under the temperatures, chemical conditions and radiation found inside the reactor.
The new programme, led by TNO, will generate the data and models needed to confirm design choices, determine cartridge lifetime and monitor materials during operation.
The partners have begun defining the research and testing plan. This will be followed by an extensive programme of materials characterisation, corrosion testing, modelling and validation. Initial work is under way at Thorizon’s facilities in Amsterdam and TNO’s laboratories in Petten, directly supporting Thorizon’s reactor design, material selection and licensing process.
Thorizon said the programme will directly support the licensing of its Pioneer demonstrator in Petten, the Netherland, and the commercial rollout of Thorizon One. Thorizon and TNO plan to collaborate with other organisations in the Dutch nuclear sector, including Delft University of Technology and NRG-Pallas. They also aim to involve international partners, such as the French Alternative Energies and Atomic Energy Commission (CEA) and the European Commission’s Joint Research Centre. These organisations could contribute expertise in materials, molten salt chemistry, irradiation, modelling, reactor engineering and licensing.
Thorizon CEO Kiki Lauwers said: “Our cartridge design makes material degradation a manageable engineering challenge. This programme will provide the independent evidence needed to validate that design and give regulators and operators confidence in material performance and cartridge lifetime. TNO is the right partner to build that qualification basis with us.”
“As a highly energy-dense, low-carbon source, nuclear energy has the potential to play an important role in a reliable energy system,” said Tjark Tjin-A-Tsoi, CEO of TNO. “New reactor technologies offer opportunities to further improve safety, sustainability and performance, while expanding the range of possible applications. These innovations can only move from concept to deployment on the basis of strong scientific evidence.”
Thorizon – a spin-off from NRG, which operates the High Flux Reactor in Petten – is developing a 250 MWt/100 MWe MSR, targeted at large industrial customers and utilities. The company plans to begin constructing its first reactor, Thorizon One, around 2030. Thorizon collaborates with industry leaders such as Orano, Tractebel and EDF, and its project has been selected by the European Commission and the French government under the France 2030 investment plan.
The Thorizon Pioneer is part of Thorizon’s roadmap to industrialise MSRs. The facility will be a smaller, non-commercial version of the Thorizon One reactor focused on validating the reactor core without electricity production. The Thorizon Pioneer will be the first nuclear molten salt installation operating in Europe, providing unique opportunities for research and development.
