Axial creep behavior of FeCrAl nuclear cladding tubes at a temperature of 600 °C

Abstract

The impacts of axial creep behavior and alloy composition on the design of safe and effective FeCrAl nuclear fuel cladding tubes remain inadequately investigated. The present work addresses these issues by evaluating the axial creep behavior of FeCrAl nuclear fuel cladding tubes in air at a temperature of 600 °C. While the creep test results represent an expected steady state creep behavior under low applied stress, the tubes are mainly in a tertiary creep state at high stress levels. Therefore, the creep test results in the steady state creep stage are fit using a power-law creep constitutive model and the Kachanov-Rabotnov model is applied for the tertiary creep stage. Comparisons between the creep test results obtained for alloys with a variety of compositions and detailed microstructural analysis of the FeCrAl nuclear fuel cladding tube specimens demonstrate that composite Laves phase particles containing Mo, Nb, and Ta are key factors generally in improving the creep properties of Fe-based alloy cladding tube specimens because the composite particles effectively restrict the motion of dislocations. However, the existence of relatively coarse secondary phase particles contributes to the formation of voids via two distinct mechanisms. Therefore, the secondary phases generated during tube fabrication must be of uniform particle sizes and be uniformly dispersed within the alloy matrix to improve creep properties while minimizing void formation.