Small-Angle Neutron Scattering Measurements of the δ Deuteride Phase in Zircaloy 4

摘要

Hydrogen pickup by Zr-based LWR fuel cladding during service leads to the formation of circumferential hydride platelet particles embedded within the Zr matrix. The precipitation of the hydride phase occurs preferentially on the water-side due to the temperature gradient within the clad wall. The non-uniform hydride morphology is known as a rim structure. Significant tensile hoop stresses within the clad wall develop during the fuel lifetime due to fission gas release and pellet-clad mechanical interaction. One potential post-service cladding failure mechanism is delayed hydride cracking (DHC) initiated by hydride reorientation under this tensile hoop stress. As a consequence, hydride reorientation and DHC have been extensively studied over the last few decades to understand the interdependencies of tensile stress, temperature, hydride morphology, and hydrogen concentration. Much of the most recent work in this area has taken advantage of 3rd generation synchrotron X-ay sources to perform in situ measurements of hydride phase stability [see for example Reference 1]. Neutron scattering based techniques offer unique advantages in the study of hydrogen in metals (typically with deuterium substituted for hydrogen) but are under utilized in the study of hydrides in Zr. We present small-angle neutron scattering (SANS) measurements of the deuteride phase in Zircaloy 4 (Zy4) here.