Hydrogen embrittlement in Zr alloy fuel cladding is a primary safety concern
for water based nuclear reactors. Here we investigated the stabilisation of
planar defects within the forming hydrides by Sn, the primary alloying element
of Zircaloy-4 used in the cladding. In order to explain formation of hydrides
and planar defects observed in our experiments, we performed atomic-scale ab
initio calculations focusing on the solute interactions with generalized
stacking faults in hcp α-Zr and fcc zirconium hydrides. Our calculations
showed that an increase in Sn concentration leads to a stabilisation of
stacking faults in both α-Zr and hydride phases. However, the solution
enthalpy of Sn is lower in the α-Zr as compared to the other hydride
phases indicative of two competing processes of Sn depletion/enrichment at the
Zr hydride/matrix interface. This is corroborated by experimental findings,
where Sn is repelled by hydrides and is mostly found trapped at interfaces and
planar defects indicative of stacking faults inside the hydride phases. Our
systematic investigation enables us to understand the presence and distribution
of solutes in the hydride phases, which provides a deeper insight into the
microstructural evolution of such alloy's properties during its service
lifetime.Comment: 17 pages, 8 figure