National Research Nuclear University “MEPhI”:

M. G. Isaenkova, Professor, Doctor of Physical and Mathematical Sciences, e-mail: MGIsaenkova@mephi.ru
M. I. Petrov, Engineer, e-mail: mipetrov.99@yandex.ru
I. V. Kozlov, Engineer, e-mail: ilya_mephist@mail.ru
A. V. Bogomolova, Engineer, e-mail: bogomolova@m-a-l.ru

The paper investigates the behavior of the hydride phase in hydrogenated tubes made of Russian zirconium E635 and E110opt alloys. The orientation and fraction of mesoscale hydrides in the alloy matrix have been described by analyzing optical metallographic images using the developed software. Metallographic images were used to assess the predominant orientation of hydrides in the axial section of the tube, as well as the surface density of the hydride phase with an increase in the concentration of hydrogen in tubes made of different alloys. It has been shown that increasing the hydrogen concentration to 600–700 wppm increases the number of radially oriented hydrides, which is associated with the development of compressive radial stress during the formation of tangentially oriented hydrides at the initial stage. Increasing the hydrogen concentration in E110opt alloy cladding tubes to 600–700 wppm leads to a change in the orientation of the α-zirconium basal axes, which results in an increase in the integral textural fR-parameter and a decrease in the f_T- and f_L-parameters. This change is due to the development of radial compressive stress and is only possible due to the activation of twinning in the grains, the basal axes of which are deflected from the compressive stress at an angle of up to 90 degrees. The results of synchrotron Debye rings and X-ray reflection diffraction analysis revealed patterns of structure and texture formation of zirconium matrix and hydrides with increasing hydrogen concentration in E110opt and E635 tube materials. Twinning by the {1012}<1011> and {1011}<1012> systems has been detected in the alloy E110opt. It reorients the basal axes at angles of 85^o and 57.2^o in the direction of compressive stress applied in the radial direction. According to the crystal lattice geometry of the α-phase, this reorientation occurs in the direction deviated from the radial direction by 30 degrees. It has been established that in E635 alloy hydrides with {001}<110> orientation are predominantly formed, but hydrides with additional {110}<011> and {110}<112> orientations are also present in smaller amounts. In the E110opt alloy there are hydrides of {001}<110> and {110}<011> orientations as well as <112> in approximately equal proportions. The presence of hydrides with a <112> partially axial textural component is due to activation in the α-phase of twinning along the {1012} and {1011} planes, in which hydrides are formed according to the established orientation relationship (0001)_{α – Zr} || {111}_{α – ZrH1.66}.

The work was carried out with the financial support of the Russian Federation represented by the Ministry of Science and Higher Education of the Russian Federation (Agreement No. 075-15-2021-1352).
The authors are grateful for the provision of samples for research to the Joint-Stock Company “Advanced Research Institute of Inorganic Materials named after Academician A. A. Bochvar” and his employees Plyasov A. A. and Saburov N. S., as well as the employees of the National Research Nuclear University MEPhI Fesenko V. A. and Mikhalev N. A.

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