Effect of Temperature and Hydrogen Concentration on the Threshold Stress Intensity Factor of Radial Delayed Hydride Cracking in Fuel Cladding
Effect of Temperature and Hydrogen Concentration on the Threshold Stress Intensity Factor of Radial Delayed Hydride Cracking in Fuel Cladding
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DOI：
10.1016/j.jnucmat.2022.153737
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发表时间：
2022-04
影响因子：
3.1
通讯作者：
A. Colldeweih;J. Bertsch
中科院分区：
文献类型：
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作者：
A. Colldeweih;J. Bertsch
三点弯曲试验提供了测量薄壁燃料包壳中轴向裂纹在径向外向内扩展的能力。通过三点弯曲，在不同温度下对含有155和305wppm氢的未辐照的zircaloy-2覆层进行机械加载，足以引发延迟氢化物开裂(DHC)，从而卸载速度足够快，以阻止进一步扩展。通过断口形貌测量裂纹前沿尺寸，并将最终载荷施加到有限元模型中。在给定平均裂纹长度和最终载荷的情况下，有限元能够反算应力强度因子。在210C-330C的温度范围内，大约6兆帕√m被计算为DHC的最小门槛应力强度因子。这一趋势表明，具有最低门槛应力强度因子的DHC的理想温度可能取决于氢浓度，并且随着试验温度的升高，门槛应力强度因子迅速增加。实验还表明，蠕变对最佳DHC的门槛应力强度因子的影响在低氢浓度下比在高氢浓度下要小。在低氢浓度下，最终固溶析出温度(TSSP)足够低，因此蠕变诱导裂纹尖端圆化的作用不如氢动力学那么显著。
Three-point bending tests provide the ability to measure the propagation of axially oriented cracks in thin-walled fuel cladding in a radial outside-in direction. Via three-point bending, unirradiated Zircaloy-2 cladding containing 155 and 305 wppm hydrogen was mechanically loaded at different temperatures, sufficient to initiate delayed hydride cracking (DHC) whereupon the unloading rate was fast enough to arrest further propagation. The crack front dimensions were measured through fractography and implemented with the final load into a finite element model (FEM). Given the average crack length and final load, the FEM was able to back-calculate the stress intensity factor. Over a temperature range of 210–330 °C, around 6 MPa√m was calculated as the minimum threshold stress intensity factor for DHC. The trend shows that the ideal temperature for DHC with lowest threshold stress intensity factors may depend on the hydrogen concentration, and that the threshold stress intensity factors quickly increase with higher test temperatures. It has also been shown that creep affects the threshold stress intensity factor for optimal DHC less for lower hydrogen concentrations than for higher hydrogen concentrations. At low hydrogen concentration, the temperature of terminal solid solubility for precipitation (TSSP) is low enough so that creep-induced crack tip rounding plays a less significant role compared to the hydrogen kinetics.