Study on Failure Assessment Curves for Safe End of Nuclear Pressure Vessels
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摘要: 建立了典型核电压力容器安全端结构的三维有限元分析模型,对假想存在于焊缝中不同尺寸的内表面周向裂纹进行有限元断裂力学分析,按英国中央电力局的内部规程——含缺陷结构完整性评定(R6)选择3(R6中失效评定图有3种,即选择1、2、3)的方法构建与安全端复杂结构、焊接坡口几何、异种金属接头区复杂材料及裂纹尺寸相关的准确的失效评定曲线(FAC)。研究发现,随裂纹深度和长度的增加,失效评定曲线下移,逐渐靠近R6选择1曲线,最大尺寸裂纹的FAC下移到了选择1曲线之下。说明对于核电安全端中的小尺寸裂纹,用选择1的通用FAC评定将得到过于保守的结果;而对于大尺寸裂纹将可能得到非保守的结果。因此安全端准确的缺陷评定应选择与裂纹尺寸相关的准确的FAC。文中对裂纹尺寸影响FAC的机理也进行了分析。Abstract: In this paper,three-dimensional finite element analysis models are built for the welded safe end of typical nuclear pressure vessels.Through finite element analysis（FEA） of fracture mechanics for the circumferential part-through surface cracks with different sizes in the weld metal,the accurate failure assessment curves（FAC） are constructed according to R6 option 3.The FACs are related to the complex structure of the safe end,the geometry of welding groove,the complex materials at weld joint region of the dissimilar metal and the crack sizes.The FEA results show that with the increase of depth and length of the cracks,the FACs gradually shift down and are close to the R6 option 1 curve,and the FAC of the largest size crack shift down below the option 1 curve.It is concluded that the option 1 curve is overly conservative for shallow and short cracks and non conservative for deep and long cracks.It is suggested that the accurate FACs which are related to crack sizes should be selected for the defect assessment of the safe end.The mechanism that how the crack sizes affect the FACs is also analyzed in this paper.
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Key words:
- Failure assessment curve /
- Safe end /
- Crack size /
- Finite element /
- Nuclear power
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