Hydride Reorientation Behavior of Zircaloy-4 Fuel Cladding
博士 === 臺灣大學 === 材料科學與工程學研究所 === 96 === The effect of radial hydrides on the mechanical properties of stress-relief annealed Zircaloy-4 cladding was studied. Specimens were firstly hydrided to different target hydrogen levels from 100 to 600 wt.ppm and then thermally cycled in an autoclave under a c...
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| Format: | Others |
| Language: | en_US |
| Published: |
2007
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| Online Access: | http://ndltd.ncl.edu.tw/handle/25793166698704743656 |
| Summary: | 博士 === 臺灣大學 === 材料科學與工程學研究所 === 96 === The effect of radial hydrides on the mechanical properties of stress-relief annealed Zircaloy-4 cladding was studied. Specimens were firstly hydrided to different target hydrogen levels from 100 to 600 wt.ppm and then thermally cycled in an autoclave under a constant hoop stress to form radial hydrides by a hydride reorientation process. The amount of radial hydrides was proportional to the number of thermal cycles. Uniaxial tension and slotted arc tension tests were conducted at room temperature to evaluate the mechanical properties of these hydrided specimens along the axial and hoop directions. The effect of radial hydrides on the axial properties of the cladding was insignificant even with the case that most hydride platelets in the 320-ppm H specimen were radially oriented. On the other hand, the cladding ductility measurements decreased as its radial hydride content increased when the specimen was tested in plane strain tension. The fracture behavior of Zircaloy-4 cladding with a mixture of radial and circumferential hydrides was discussed. A reference hydrogen concentration for radial hydrides in the cladding was defined for assessing the fuel cladding integrity based on a criterion of the tensile strength 600 MPa. The reference hydrogen concentration increased with the specimen (bulk) hydrogen concentration to a maximum of ~90 wt.ppm at the bulk concentration ~ 300 wt.ppm H and then decreased towards higher concentrations.
The formation of radial hydrides in Zircaloy-4 cladding was also studied. The thermal cycling was observed to have more significant effect on hydride reorientation than the isothermal treatment. Based on the experimental data, a thermodynamic model was proposed to elucidate the stress reorientation behavior of hydrides in Zircaloy cladding. According to the model, the bounds of stress and temperature to stress reorientation of hydride precipitates were developed. The threshold stress for hydrides to reorientation was a function of solution temperature and specimen hydrogen concentration.
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