First Results of Characterization of 9Cr-3 WVTiTaN Low Activation Ferritic/Martensitic Steel

Ferritic/martensitic steels with 9-12 wt%Cr are favored candidates for fuel cladding tube and in-core applications for construction of supercritical water cooled reactor. 9Cr-3WVTiTaN reduced activation ferritic/martensitic steel, designated as China Nuclear Steel-I (CNS-I), is patterned after T91 steel. The idea of low activation material and microalloy technology were introduced into the design of the steel. A characterization program is being performed to determine the relevant mechanical and physical metallurgical properties in order to qualify it for fuel cladding and in-core applications in supercritical water cooled reactor. The hardening, tempering and transformation behavior of CNS-I steel was investigated. The steel has advantages in tensile properties at elevated temperature relative to zircaloy that has been widespread applied as cladding material in conventional light water reactors. CNS-I steel exhibits comparable tensile properties and impact toughness to T91 steel which exhibites availability in the present fission reactors and fast breeder reactor but includes undesired elements such as molybdenum and niobium for reduced activation.