Abstract
Specimens of Zr1Nb and Zry-4W were pre-oxidized first for 360 days in steam at 425 °C and were then exposed for 3 min to 1200 °C in steam, simulating loss of coolant conditions. In this way, the oxide thickness was more than doubled. The I-V characteristics, measured up to 90 V at temperatures up to 180 °C, revealed the formation of double layers, consisting of dark monoclinic oxide with 1.3 eV activation energy near the metal, and of a whitish surface phase with only 0.5 eV, for both samples. The I-V characteristics of Zr1Nb showed normal behavior, whereas Zry-4W changed from an unusual sub-linear form at low temperatures and voltages to normal space-charge limited currents at higher temperatures and voltages. Observation of the injection and extraction currents in the Zry-4W sample showed abnormally high negative zero voltages produced by extraction after former injection.
Highlights
In a LOCA-type accident in atomic reactors, the cladding of the fuel cells is exposed to high temperature shock for several minutes, and it is vital to know possible changes in the material properties influencing the safety conduct
The aim of this work is to investigate the oxide layers formed by the thermal shock, and to compare their properties with the original pre-oxidized layers
In order to simulate LOCA conditions, samples of Zr1Nb and of Zry-4W pre-oxidized in steam at 425 °C for 360 days were exposed to 1200 °C in steam for 3 minutes
Summary
In a LOCA-type accident in atomic reactors, the cladding of the fuel cells is exposed to high temperature shock for several minutes, and it is vital to know possible changes in the material properties influencing the safety conduct. The aim of this work is to investigate the oxide layers formed by the thermal shock, and to compare their properties with the original pre-oxidized layers. In order to simulate LOCA conditions, samples of Zr1Nb and of Zry-4W pre-oxidized in steam at 425 °C for 360 days were exposed to 1200 °C in steam for 3 minutes. The oxide layer thickness increased from 33.3 mm to 78.8 mm for Zr1Nb, and from 35.3 mm to 78.7 mm for Zry-4W. The grown oxide is of different color, and at the interface a very thin layer of metallic tin could be observed. Oxygen diffused into the underlying zirconium with 30 % at the interface, and structural changes could be asserted down to 100 mm, Table 1
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