Effect of Zr on the microstructure of corrosion resistant ODS steels

Radiation-resistant steels are essential for the development of next-generation fission and future fusion energy systems. The incorporation of nano-particles in metallic matrices by powder metallurgy processing is widely employed for the development of radiation-resistant steels, and continues to be the subject of intense research worldwide. The two most critical properties of these materials for application in these future reactor designs are the maintenance of high strength at temperatures above the softening point of conventional steels and the reduction in sensitivity to radiation-induced He embrittlement. Oxide dispersion strengthened (ODS) steels show considerable promise in both properties. The distribution, chemistry and shape of the oxide nanoparticles, and their influence on the matrix chemistry and irradiation response, play a crucial role in many of the improved properties. However, there is considerable disagreement in the literature on the nature of these nanoparticles as a function of alloy chemistry and manufacturing process, and the precise mechanisms by which they respond to irradiation damage. There is also a requirement to develop new ODS steels with improved corrosion resistance specifically for fuel cladding materials for closed fuel cycles. Recently, high Cr ODS steels with Al additions have been developed for use in highly corrosive environments, but their high-temperature strength is poor. First principles calculations by one of the partners indicate that adding Zr to these alloys may refine and increase the number density of oxide particles by forming Y-Zr-O phases. We predict that this would improve the high temperature strength while maintaining the improved corrosion resistance and irradiation performance. It is this prediction that we wish to test in this new project.

This is a joint project between a major Indian nuclear research laboratory and the Materials Department in Oxford University. Our aim is have a significant impact on the development of ODS alloys for high temperature advanced nuclear fission reactors. India has its own ambitious national Fast Breeder Reactor programme through which developments in the project can be exploited, and the Oxford team have strong connections to the European joint research programme on Generation IV nuclear fission. International research on the Generation IV systems is coordinated by GIF, and within Europe, the Technology Platform on Sustainable Nuclear Energy (SNETP) defines the common European vision on both the role of nuclear energy and R&D needs for the safe, sustainable, and efficient use of nuclear fission technology. The European Sustainable Nuclear Industrial Initiative (ESNII), launched in November 2010, focuses on advanced fast reactors.

The Oxford-Bristol Nuclear Research Centre (NRC) (http://www.nrcuk.net), was launched in November 2011 and grew from the increasing number of informal collaborations between the two universities and their existing strategic alliances with nuclear companies including EDF-Energy and Rolls-Royce and the firm plans for new nuclear build in the South of England. Grovenor is the director of the NRC in Oxford. The NRC is a member of NUGENIA, which provides a route to lead or participate in coordinated R&D projects in support of current (i.e. second) and third generation nuclear systems. With the outputs with this new project Oxford will be in a strong position to contribute to future NUGENIA-supported research.

The fundamental research and development to underpin the activities for Generation IV fission, particularly ESNII, is now concentrated within the EERA Joint Programme on Nuclear Materials (JPNM) and is presently supported within Euratom, via the FP7 MATTER project. Its purpose is to improve the European Union's energy research capabilities, and particularly to accelerate the development of energy technologies to the point where they can be taken up in industry-driven research. The activities of EERA seek to streamline and coordinate national and European energy R&D programmes through the pooling and integration of activities, resources and funding. The EERA JPNM was launched in June 2011, since when Prof. Marrow from Oxford Materials has been the UK member of its Steering Committee. One major R&D challenge to be addressed is the availability of appropriate structural materials that are able to withstand the severe conditions of high temperature and thermal gradients, high irradiation doses, long lifetime and corrosive environments. We are thus well placed to integrate our research on ODS materials into these international activities.