Estudio teórico / numérico de la difusión de hidrógeno en aleaciones base Zr-Nb

BELTRAMO, GUILLERMO N.; RAMUNNI, VIVIANA P.; PASIANOT, ROBERTO C.

Anales AFA

Asociación Física Argentina

Lugar: Tandil; Año: 2021 vol. 0 p. 1 - 11

0327-358X

Within the framework of the delayed hydride cracking phenomena reported for the pressure tubes of CANDU-type nuclear reactors, we study the influence of the Zr-β (∼ 20%Nb - ∼ 80%Zr) continuous phaseon the hydrogen diffusion coefficient, D H , through the Zr-α - Zr-β biphasic alloy. We propose an improved phenomenological model for D H with respect to those founded in the literature. Furthermore, we studythe influence of the Nb content on D H for the cubic phase Zr-β, employing the transition state theory furnished with ab-initio parameters provided by the SIESTA code. In particular, we consider 9 orderedalloys with different Nb content and compute effective activation energies as determined by Arrhenius fits for each alloy. We find that activation energies vary in a non-monotonic way as Nb content increases,reaching a maximum value at about Zr-50%Nb. Finally, we observe that the predicted and measured larger diffusivity along the tube axis vs the radial direction, is consistent with the material texture. Moreover,we conclude that the loss of continuity of the Zr-β sheets present in the tube microstructure, is consistent with the decrease of D H in time at a given temperature.