Effect of the inner liner on the hydrogen distribution of zircaloy-2 nuclear fuel claddings

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

“…The slowcooled sample has been used as a reference sample in order to understand the precipitation of hydrides in the liner without external variables such as a stress field or an oncoming crack. These results specifically expand upon the neutron radiography studies on liner cladding under similar slow-cooling conditions where hydrogen concentrations were quantified in the liner and substrate showing the magnitude of hydrogen diffusion and precipitation within the liner [12,13]. The primary reason, as stated in the previous references, for the strong hydrogen precipitation within the liner is due to chemical potential differences in the liner and substrate.…”

“…While both sample crack velocities were extremely slow at 100 • C, the material with an inner liner cracked at about one third of the velocity as the cladding without an inner liner. The decreased velocity is likely explained by the reduced hydrogen concentration in the substrate as a result of significant hydrogen diffusion towards, and precipitation within, the liner material during cooling to the test temperature [13]. It can otherwise be understood as a reduced hydrogen source for DHC as the crack propagates within the hydrogen-depleted substrate.…”

“…Additionally, the tip of the DHC crack in material with an inner liner contains more γ-hydride phase than DHC crack tips in material without an inner liner. As it well known that the hydrogen source for DHC within the substrate is low (due to the absorption into the liner) [13,33], the hydrides which do precipitate at the DHC crack can be postulated to be at minimum hydrogen-zirconium stoichiometry levels, resulting in higher amounts of the γ-hydride phase. Table 5 presents the γ/δ-hydride ratios of the various ROIs defined in Figs.…”

“…Such inner layer has been defined in the nuclear industry as an inner 'liner' and is joined through metallurgical methods to the primary structure of the fuel cladding, which is defined as the 'substrate' [11]. In the context of hydrogen uptake, the effects of a liner on hydrogen diffusion and precipitation kinetics has also been explored [12,13] showing that the hydrogen is strongly attracted to the liner-substrate interface. The hydrogen subsequently precipitates at high concentrations within the liner material.…”

The INCHAMEL facility – a new device for in-situ neutron investigations under defined temperatures with applicable mechanical load

“…The non-destructive character of neutron imaging and the high penetration depth of neutrons in many technical relevant materials allow in-situ measurements using special sample environments [1,2,3,4]. To assess the material's state of nuclear fuel assemblies after their dry storage over several decades, the need of in-situ neutron radiography experiments of the hydrogen re-distribution under mechanical load at defined temperature arises [3].…”