Delayed hydride cracking in Zircaloy-2 with and without liner at various temperatures investigated by high-resolution neutron radiography

Zirconium hydride phase mapping in Zircaloy-2 cladding after delayed hydride cracking

“…In addition, the hydrides of a slowcooled sample, acting as an unstrained reference, with an inner liner was measured. The results compliment recent neutron radiography of DHC cracks improving the spatial resolution of mapped hydrides and enabling phase identification [15].…”

“…The cladding material was hydrogenated in tube sections through gaseous charging using a Sievert's type apparatus and heat treated in order to homogenize the hydrogen distribution as described in the following references [12,15,30]. Specific hydrogen content was then measured through destructive testing, Hot Vacuum Extraction (HVE), using a LECO device at the Paul Scherrer Institut (PSI) resulting in average concentrations as seen in Table 2.…”

“…The samples were first fatigue pre-cracked at room temperature according to previously reported procedures [15,32]. Subsequent to the propagation of the sharp initiation crack, the samples were mechanically unloaded and heated above the respective temperature of terminal solid solubility of hydrogen for dissolution (TSSD) and held for 1 h prior to cooling at 30 • C/h until reaching the test temperature [15,[32][33][34]. Following the stabilization of the test temperature, the starting mechanical load l o was applied.…”

“…Thus, deeper understanding of the DHC phenomenon in a large range of temperatures is essential for safe storage [14]. This includes the fundamental understanding of hydrogen diffusion and hydride precipitation at various temperatures, whereas research on hydride precipitation and phase analysis has already been initiated [15][16][17][18]. However, due to the challenging test conditions and large amount of time required for low temperature tests, the DHC phenomena specifically at low temperatures have not been sufficiently studied up to now.…”

“…Recent literature has reported on various dependencies of DHC hydride precipitation showing the hydrogen concentration gradients around DHC cracks with neutron radiography measurements [15] as well as multi-physics modeling [26,27], giving hints to possible changes in phases or precipitation kinetics. As the temperature range which DHC can occur encompasses the precipitation temperatures for both δ and ɣ phases [28], a change in the mechanical properties between different hydride phases, like fracture toughness [22], could lead to a change in mechanical stability of the overall system depending on the temperature.…”