由於燃料丸端面製造缺陷問題，導致燃料丸於運轉期間對護套造成較高之應力集中且產生局部低溫現象，使氫原子隨溫度梯度往低溫區擴散並於護套外側析出脆性之氫化鋯，致使初始裂縫於護套外側形成。在持續受到溫度與壓力的作用下，氫化鋯將產生方位重排的現象，在氫化鋯持續析出的成長階段，氫化鋯會逐漸排向不利於母材之機械性質方向，而裂縫尖端前之氫化鋯會排向有利於裂縫成長的徑向方位，使裂縫持續由外往內成長，成為不預期的破損機制。
本研究利用ANSYS有限元素分析軟體將燃料丸與護套間機械交互作用之問題導入模擬分析中，在燃料丸有缺角的情況下，建立含有初始裂縫之護套模型與具脆性之氫化鋯模型於裂縫尖端前，並設定適當之邊界條件，分析氫化鋯對護套裂縫之影響。其分析內容包含：氫化鋯與裂縫之間的水平距離、垂直距離、氫化鋯面積大小、有無環向氫化鋯分布及燃料丸的缺角變化。觀察各項分析之應力強度因子(KI)及J積分之分析結果，並探討氫化鋯對護套裂縫之影響。本研究中還有探討氫化鋯之不同裂開型態對護套裂縫造成之影響，並觀察應變能密度分布之結果，探討其對護套裂縫成長之影響，使護套之裂化機制更具完整性。

The pellet fabrication defect “Missing Pellet Surface (MPS) ” became an important failure mechanism in the past decade, and the unexpected high stress induced on cladding inner surface was identified as “non-classical PCI”. The failure root cause analysis of some leaking rods indicated that hydrides may play an important role of the outside-in cracking. The MPS will cause the temperature gradient on the cladding and it will induce the hydrogen re-distribution, and the precipitated hydride could initiate cladding crack and rod failure.
Our study proposed a methodology to investigate the effect of hydride on the crack propagation in fuel cladding. The analysis was modeled based on an outside-in crack with radial hydrides located near its crack tip. The finite element method was used in the calculation. In this study we applied stress intensity factor KI and J integral to evaluate the crack stability. The parameters employed in the analysis included the location of radial hydride, hydride dimensions, degree of MPS, and the presence of circumferential hydride. In this study we also discussed the hydride split in different kind of ways and applied the strain energy density theory to evaluate the crack stability.
This study is helpful to understand the hydride effect of Pellet-Cladding Mechanical Interaction (PCMI) and contains a reliable cladding integrity evaluation for the effects of zirconium hydride on cladding crack.

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