High-reliability safety assessment for nuclear pressure vessels by preventing both brittle crack initiation and arrest

To ensure the structural integrity of thick-walled pressure vessels during extended service life, a “double integrity” assessment strategy can be implemented to achieve a High-Reliability Structural-Safety Assessment (HSA). This approach involves not only the prevention of brittle crack initiation but also the inhibition of crack propagation. The ability of a material to resist further crack extension is generally referred to as crack arrest toughness. Investigating crack arrest toughness is essential for reliable safety evaluations during long-term operation. This study provides a comprehensive analysis of the crack arrest toughness of 18MnD5, a commonly used nuclear-grade material in pressure vessels. The research examines the influence of microstructural characteristics and crack propagation mechanisms on crack arrest behavior. Experimental tests were developed in accordance with ASTM E1221-23 to generate crack arrest toughness curves for high-reliability microalloyed low-alloy (HRML) steel under varying loading conditions. Microscopy techniques were employed to analyze the impact of microstructural changes on the material’s crack arrest performance. Furthermore, numerical simulations were conducted to model crack initiation and arrest in thick-walled pressure vessels under typical reactor operating and accident scenarios. The findings indicate that crack arrest toughness is significantly affected by microstructural features, including grain boundary characteristics, phase distribution, and carbon segregation. Specific microstructural attributes were found to promote localized plastic deformation, thereby diminishing the material’s capacity to effectively arrest cracks.