Ni-based ODS alloys for Molten Salt Reactors

Although light water reactors (nuclear reactors cooled with water) have historically been the most popular type of reactor, the threat of a nuclear meltdown and hydrogen gas explosion is a continuous concern, especially in the wake of the Fukushima Daiichi nuclear power plant accident in 2011. One nuclear reactor design that is safer and more efficient than the light water reactors designs is the molten salt reactor (MSR) where molten salt is used as a coolant and in many designs, as a liquid fuel. There is no worry of a nuclear meltdown because the fuel is already in liquid form and with liquid fuel, the reactor can be operated at much higher temperatures up to around 750 C leading to a higher reactor efficiency. These molten salts make excellent coolants due to a higher volumetric heat capacity compared to pressurized water. Furthermore, since the liquid salt is used as a coolant instead of water, there is no risk hydrogen production that could lead to a hydrogen explosion. Whilst there are many advantages to these reactors they have major materials challenges. The molten salt is corrosive and will attack and essentially dissolve some materials, including many common grades of steel, it comes into contact with. This has limited the use of these reactors to test reactors, initially developed for use in nuclear planes! There is now much interest in using these reactors for power generation and several companies actively developing new designs and working to build concept plants.
If these reactors are to be used commercially then new grades of nickel alloys (which do not suffer such corrosive attack in contact with the salt) need to be developed. Previous grades of nickel alloy have suffered from embrittlement caused by the helium which is produced by nuclear reaction in the reactor. This work will design, develop and process new nickel alloys which contain nano-meter sized oxide based particles which effectively capture the helium, trap it and stop it causing premature failure. In addition these particles make the nickel stronger at high temperature allowing more efficient reactor operation. By developing this material we will accelerate the development and deployment of this safer and potentially cheaper reactor design.

Moten salt reactors are a nuclear fission reactor design which are a leading candidate for the next generation of nuclear reactors ( both so called GEN IV and small modular designs). Such reactors will have higher efficiency and be safer than current gas or water cooled systems. However they are currently restricted in operation by a lack of suitable materials for. The environment is highly corrosive and this combined with high levels of neutron damage means there is a need for new alloy concepts to be developed. Steels can not be used as it has been found that the chromium traditionally used for corrosion protection dissolves in the molten salt. Nickel alloys while more corrosion resistant suffer from two main drawbacks. A large amount of helium production during neutron irradiation and lack of strength at temperatures above 500 Celsius . To overcome these problems we will develop an oxide dispersion strengthened nickel alloy. This concept has been shown to improve helium management and strength in ferritic steels and we expect the same to be true in these nickel alloys.

This grant will accelerate the development of ODS nickel and further understand their ability to act under the highly corrosive environments expected in a molten salt reactor. The acceleration of deployment of new designs of nuclear reactors has the potential to provide base load power generation along side renewable options. This will reduce the reliance on fossil fuels and help combat climate change. MSRs are attractive as a so called small modular concept. This raises the possibility of them being sited in remote communities and other non-traditional nuclear sites, furthering the impact nuclear can have on climate change.
Within the UK, ODS nickel is of interest to Moltex who are a leading SME with a awarding winning molten salt reactor design. This work has the potential to increase the operational temperature and neutron spectrum of their reactor leading to increased efficiency. They have provided corrosion testing support to this project. ODS nickel alloys have previously been studied for use in the aerospace industry. We will use our strong links with Rolls Royce to keep make sure developments made in this project can be taken forward into other industries if applicable.
Oxford University Innovation, the University of Oxford's Technology Transfer Department, will work with us to exploit any intellectual property of commercial potential of our research. This will include both alloy design and processing methods. As well as any developments made in the high temperature testing and analysis techniques to quantify chemical changes. These methods are of interest to many of our existing partners including MicroMaterials, EdF and CCFE and we will communicate developments and possible opportunities with them throughout the project through yearly open meetings.