Hydride Formation in Neutron Irradiated Material under Reactor in Conditions

P. VIZCAÍNO; A.V. FLORES; J.R. SANTISTEBAN; M.A. VICENTE; A. TOLLEY; A. CONDÓ; J. ALMER; A. BARUJ; A.D. BANCHIK

Busan

Workshop; Third RCM on Spent Fuel Performance Assessment and Research (SPAR-III) ? IAEA; 2013

International Atomic Energy Agency

Hydride reorientation can occur as a result of the following sequence of events. During reactor operation, part of the elemental hydrogen created by oxidation of the cladding by water is absorbed by the zirconium-based alloy, and once the solubility limit of hydrogen in the cladding material matrix is reached, hydrogen precipitates in the form of hydride platelets predominantly aligned in the circumferential and axial directions. Additional circumferential-axial (or simply ?circumferential?) hydrides precipitate during reactor shutdown due to the decrease of the hydrogen solubility limit with temperature.   Following wet storage in pools at prevailing temperatures of ~30-40°C, spent fuel is moved to dry storage or transported to a centralized storage or reprocessing facility. Dry storage and/or transport operations may cause significant increases in cladding temperature: peak cladding temperatures of up to 400°C (dry storage) or up to 420°C (transport) are generally considered. The temperature increase from pool conditions to dry storage/transport conditions results in hydride dissolution and in a corresponding increase of the hydrogen in solid solution in the zirconium alloy matrix up to the hydrogen solubility limit. The temperature increase also leads to an increase of the rod internal pressure. Subsequent cooling during dry storage or re-wetting after transportation causes hydrogen in solid solution in the cladding materials to re-precipitate, but possibly aligned in the radial and axial directions (or simply ?radial?) due to the influence of the tensile hoop stress in the cladding, caused by the internal rod pressure that is no longer compensated by external means such as the coolant pressure in the reactor.