Event Timeslots (1)

Day 1 – June 20
Molten salt reactors (MSRs) are a leading generation IV fission reactor design, on account of their heightened operating efficiency and improved safety in comparison to light water reactors (LWRs). Critical to the implementation of this technology is the development of structural materials capable of withstanding the high temperature, severely corrosive, and highly irradiating environment inside a MSR.

The commercially available Hastelloy family of Ni superalloys have already, historically, been proven as promising candidate materials for use in MSRs; they possess superior high temperature mechanical properties. In particular, variants of Hastelloy N (Ni-7Cr-16Mo) are shown to exhibit minimal corrosive attack in hot fluoride salts. However, Ni alloys are vulnerable to irradiation embrittlement, most significantly, that induced by helium segregation. Helium is an unavoidable product of reactor operation, produced through transmutation reactions, and thus there is a drive to develop a Hastelloy variant which is resistant to the embrittling effects of He.

Nano-sized oxide-based particles have been shown to act as effective He traps in oxide-dispersion-strengthened (ODS) steels, preventing premature component failure caused by He embrittlement. Consequently, the possibility of combining the irradiation benefits of ODS particles with the corrosion and mechanical properties of Hastelloy is a promising avenue in MSR material research.

A joint venture by the University of Oxford, North Carolina State University, the University of California-Berkeley, the University of Idaho and Idaho National Laboratory (INL), is aiming to design, test and characterise candidate ODS nickel alloys for potential use in MSRs. Candidate alloys have been fabricated used powder metallurgy, combining Hastelloy with yttria powder, before being subjected to mechanical testing and multi-level characterisation. This talk will present results from initial investigations, with a particular focus on the use of atom probe tomography, to demonstrate the extent to which yttria incorporation has been successful; a critical factor in determining the success of these alloys in trapping He, and thus preventing irradiation-induced embrittlement.