Desorption of Implanted Deuterium in Heavy Ion-Irradiated Zry-2

To understand the degradation behavior of light water reactor (LWR) fuel-cladding tubes under neutron irradiation, a detailed mechanism of hydrogen pickup related to the point defect formation (i.e., a-component and c-component dislocation loops) and to the dissolution of precipitates must be elucidated. In this study, 3.2 MeV Ni3+ ion irradiation was conducted on Zircaloy-2 samples at room temperature. Thermal desorption spectroscopy is used to evaluate the deuterium desorption with and without Ni3+ ion irradiation. A conventional transmission electron microscope and a spherical aberration-corrected high-resolution analytical electron microscope are used to observe the microstructure. The experimental results indicate that radiation-induced dislocation loops and hydrides form in Zircaloy-2 and act as major trapping sites at lower (400–600 °C) and higher (700–900 °C)-temperature regions, respectively. These results show that the detailed microstructural changes related to the hydrogen pickup at the defect sinks formed by irradiation are necessary for the degradation of LWR fuel-cladding tubes during operation.

Investigation on Breakaway Oxidation Behavior of CZ Alloys

Breakaway oxidation is a potential fuel failure mechanism during a loss-of-coolant accident (LOCA), especially small-break LOCA. Two kinds of new advanced zirconium alloy, CZ1 and CZ2, were developed by China Nuclear Power Research and Technology Institute of China General Nuclear Power Group. The breakaway oxidation behavior of CZ1 and CZ2 was studied. The outer surface of all samples was examined visually and photographed. After 2730s oxidation in steam, the outer surface of CZ1 alloy sample and CZ2 alloy sample remained lustrous-black. The outer surface of CZ1 sample oxidized in steam at 1000 °C for 4181s was grey, but under the same experimental conditions the outer surface of CZ2 sample was still lustrous black. The hydrogen pickup content of different oxidation time was measured. The samples with grey appearance showed significant hydrogen pickup. The microstructure was observed by optical microscope. Evolution of oxide structure was described, and the mechanism was discussed.

Small-angle neutron scattering measurements of δ-phase deuteride (hydride) precipitates in Zircaloy 4

Small-angle neutron scattering (SANS) measurements have been performed under ambient conditions to characterize deuteride (hydride) particles in Zircaloy 4, a fuel cladding material used in pressurized light-water nuclear reactors. Hydrogen pickup by the cladding leads to a rim structure in which large circumferential hydride plate-like particles preferentially form on the cooler water-side region of the cladding. Deuterium substitution has been used to increase the coherent response and decrease the incoherent background of the SANS measurements. Four bulk deuterium concentrations were investigated, approximately 100, 400, 500 and 1000 parts per million by weight (w.p.p.m.) deuterium, as well as a zero-deuterium-concentration reference sample. The net SANS response from the deuteride phase was determined at all concentration values after subtraction of the reference SANS response, which effectively subtracted the strong scattering from second-phase particles in as-received Zircaloy. The net SANS response consisted of strong Porod scattering from deuteride particles over the entire measured Q range (0.005–0.4 Å−1). The net SANS response was anisotropic at concentrations greater than 100 w.p.p.m. and required elliptical averaging analysis. A significant sample orientation effect on the intensity of the SANS response was observed, due to preferential alignment of deuteride particles. The effect of ex situ applied stress at elevated temperature on deuteride phase dissolution and reprecipitation was investigated; a weak effect was observed with SANS that could not be confirmed by optical microscopy.