Noriyuki Y. Iwata

High Burnup Fuel Cladding Materials R&D for Advanced Nuclear Systems: Nano-sized oxide dispersion strengthening steels

Cladding materials development is crucial to realize highly efficient and high-burnup operation over 100GWd/t of so called Generation IV nuclear energy systems, such as supercritical-water-cooled reactor (SCWR) and lead-cooled fast reactor (LFR). Oxide dispersion strengthening (ODS) ferritic/martensitic steels, which contain 9–12%Cr, show rather high resistance to neutron irradiation embrittlement and high strength at elevated temperatures. However, their corrosion resistance is not good enough in SCW and in lead at high temperatures. In order to improve corrosion resistance of the ODS steels in such environment, high-Cr ODS steels have been developed at Kyoto University. An increase in Cr content resulted in a drastic improvement of corrosion resistance in SCW and in lead, while it was expected to cause an enhancement of aging embrittlement as well as irradiation embrittlement. Anisotropy in tensile properties is another issue. In order to overwhelm these issues, surveillance tests of the material performance have been performed for high Cr-ODS steels produced by new processing technologies. It is demonstrated that high-Cr ODS steels have a high potential as fuel cladding materials for SCWR and LFR with high efficiency and high burnup.

Microstructure and Tensile Properties of ODS Ferritic Steels Produced by Mechanical Alloying in Argon and Hydrogen Gas Environments

Two types of oxide dispersion strengthened (ODS) ferritic steels have been produced by mechanical alloying (MA) either in argon or in hydrogen atmosphere, and vacuum hot pressing (VHP). A drastic reduction in the oxygen and nitrogen contents after VHP was strongly affected by hydrogen gas used as the MA atmosphere. MA in hydrogen was found to be effective for refining the steel matrix and enhancing the tensile ductility of the ODS ferritic steels.