Effect of ion and neutron irradiation on oxide of PHWR fuel tube material

The effect of heavy ion irradiation on the stability of oxide phase of autoclaved Zircaloy 4 fuel tube material, has been studied using Glancing angle X-ray diffraction (GIXRD) technique after 306 KeV Ar⁺⁹ ions irradiation at a dose of 3 × 10¹⁹ Ar⁺⁹/m². To estimate the extent of damage, a simulation was carried out using "Stopping and Range of Ions in Matter (SRIM-2008)" computer program based on the Monte Carlo method. For the first time, the oxide formed in ₀n¹ irradiated fuel tube after 7600 MWD/T burn up in Pressurized Heavy Water Reactor (PHWR) has been characterized using GIXRD technique. The advantage of this technique is that the stress-induced phase transformation, which normally occurs during metallographic sample preparation for optical and electron microscopy, is eliminated. The un-irradiated autoclaved oxide in the steam environment (415 °C and 500 °C), both uniform as well as nodular oxide has been characterized using GIXRD, X-ray photo-electron spectroscopy (XPS), scanning electron microscopy (SEM) attached with Energy Dispersive spectroscopy (EDS). Cross-sectional transmission electron microscopy has been carried out in uniform oxide before and after heavy ion irradiation. It is observed that heavy ion and neutron irradiation induce monoclinic to tetragonal phase transformation in the oxide. Presence of significant fraction of tetragonal ZrO₂ phase as well as sub-oxide Zr₃O has been identified in the oxide layer near oxide-coolant interface in ₀n¹ irradiated in-pile sample whereas in unirradiated autoclaved oxide these phases are present in a small fraction near the oxide-metal interface. XPS analysis indicates the difference in the chemical state of alloying element in the oxide when autoclaving is carried out at different temperatures.