Abbreviations

CTT Continuous cooling transformation

CEN-SCK Centre d’Etude de l’energie Nucleaire — Studiecentrum voor Kernenergie

4.08.1 Introduction

Recent progress in oxide dispersion strengthened (ODS) steels produced by mechanical alloying (MA) techniques allows them to be used as fuel cladding in sodium-cooled fast reactors (SFR). The thermally stable oxide particles dispersed in the ferritic matrix improve the radiation resistance and creep resistance at high temperature. As a result, ODS steels have a strong potential for high burnup (long-life) and high — temperature applications typical for SFR fuels. The attractiveness of ODS steels is due not only to the nanosize oxide particles composed of Y—Ti—O atoms but also to their controlled micron-size grain mor­phology. We review existing knowledge on the crys­talline structure and lattice coherency of these nanosize particles with their surrounding matrix, since these factors dominate the dispersion and strength-determining mechanism through dislocation interaction. The development of manufacturing pro­cesses is a principal issue for hardened ODS steels to realize long, thin-walled ODS steel cladding on pro­duction scales. There was the long-standing problem in low hoop strength due to the extremely elongated fine grains parallel to the rolling direction. To soften hard­ened cold-rolled products and modify their grain morphology, martensitic 9Cr-ODS steels and ferritic 12Cr-ODS steels have been developed. Current prog­ress in the development of these ODS steel claddings, including their relevant mechanical properties, for example, tensile and creep rupture strengths in the hoop directions, and irradiation performance, is reviewed. The development of Al-added high Cr — ODS steel cladding is also addressed, with a focus on superior resistance to oxidation and corrosion in a lead — bismuth eutectic (LBE), and supercritical pressurized water (SCPW) in the international Generation IV advanced nuclear power system. Nanocluster ODS steels,1 for example, 14YWT, etc., for fusion blanket structure materials, are not addressed in this chapter.