Ni-based ODS alloys for Molten Salt Reactors

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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.