An atom probe tomography study of the chemistry of radiation-induced dislocation loops in Zircaloy-2 exposed to boiling water reactor operation

J Eriksson,G Sundell,P Tejland,H.-O Andrén,M Thuvander

doi:10.1016/j.jnucmat.2021.152923

Abstract

This study is complementary to previous atom probe tomography (APT) studies of irradiation effects in the zirconium alloy Zircaloy-2. Using APT in voltage pulse mode, a difference in morphology was observed between clusters of Fe and Ni and clusters of Fe and Cr in Zircaloy-2 exposed to a high fast neutron fluence in a commercial boiling water reactor. The Fe–Ni clusters were disc-shaped with a diameter of 5–15 nm, whereas the Fe–Cr clusters were spheroidal with a diameter of approximately 5 nm. Both types of clusters appeared to be located at irradiation-induced <a>-type dislocation loops aligned in layers normal to the <c>-direction. The concentration of Fe was higher in the Fe–Cr clusters than in the Fe–Ni clusters. The dilute Fe–Ni clusters, which seem to be segregation of Fe and Ni inside the loops, had formed on all three families of first-order prismatic planes with some deviation from perfect <c>-axis alignment. The Fe–Cr clusters might be very small precipitates with a nucleation associated with the loops.

Highlights

Zirconium alloys are used in nuclear reactors as cladding tubes for the nuclear fuel
As the change in atomic positions of Zr is small between α-Zr and hydride phases [59,60], the microstructural features observed in our analysis can be assumed to be representative of the metal during reactor operation
In this study of a region rich in Ni and Fe in the metal close to the metal/oxide interface in Zircaloy-2 exposed to boiling water reactors (BWRs) operation, clusters of Fe and Ni and clusters of Fe and Cr aligned in layers parallel to the basal planes have been observed using atom probe tomography (APT) in voltage mode

Summary

Introduction

Zirconium alloys are used in nuclear reactors as cladding tubes for the nuclear fuel. In boiling water reactors (BWRs) the alloy Zircaloy-2 is commonly used. The neutron radiation during reactor operation induces radiation damage in the form of small dislocation loops in the hexagonal Zircaloy matrix, the smallest only a few nm in size [1]. In neutronirradiated Zr and Zr alloys, the Burgers vector of -loops has been observed to be 1/3 [1,2] and the Burgers vector of -component loops 1/6 [1,3]. The -loops are found on or close to the prismatic lattice planes, and they align in arrays forming layers that are parallel to the basal planes [1,2]. The -component loops are found on the basal planes [1,3]

Results

Discussion

Conclusion