Hydride Reorientation Behavior of Zircaloy-4 Fuel Cladding
Date Issued
2007
Date
2007
Author(s)
Chu, Hou-Chin
DOI
en-US
Abstract
本研究探討氫化鋯方位重排行為及其對護套材料機械性質的影響。未照射鋯合金護套樣品均勻氫化至100至600 wt.ppm等預定濃度後，於自動 畬t壓系統中以熱循環熱處理，藉施加於護套上之環向應力，誘引氫化鋯析出面沿護套半徑向方位析出。氫化鋯方位重排程度隨熱循環熱處理次數增加而增加，最大轉向程度則與樣品原先氫含量有關。方位重排後，樣品製作成單軸向拉伸試片和槽化弧狀拉伸試片，以評估不同比例徑向氫化鋯對護套軸向及環向機械性質的影響。研究結果顯示，即使320 ppmH樣品內氫化鋯完全轉成徑向，徑向氫化鋯對護套管軸向機械性質影響不明顯。然而，護套環向機械強度與延性均隨樣品中徑向氫化鋯比例增加而減少，但相同條件所得測試結果出現較大的差異，此現象與徑向氫化鋯型態及分佈有關。根據實驗結果，評估護套合金維持完整性所允許樣品最大徑向氫化鋯濃度，即參考濃度。由於不同含氫量樣品氫化鋯排情形不同，樣品之徑向氫化鋯參考濃度隨樣品本身含氫量有先升後降趨勢。根據上述方位重排實驗結果建立徑向氫化鋯析出之熱力學模式，並據此推演護套材料發生氫化鋯方位重排所需之應力及溫度條件。
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.
Subjects
鋯四護套合金
徑向氫化鋯
應力方位重排
機械性質
熱力學模式
Zircaloy-4 cladding
radial hydride
stress reorientation
mechanical property
thermodynamic model
Type
thesis