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<p>The lower head of reactor pressure vessel (RPV) will be subjected to high-temperature creep under extreme accident conditions due to the implementation of in-vessel retention (IVR) mitigation measures. In this scenario, the change in internal pressure has a significant impact on the creep behavior of the RPV. Therefore, the paper investigates the creep performance of RPV material 16MND5 steel at 600 and 700 °C under variable load. The effects of load variations on creep rate and lifetime at elevated temperatures are analyzed, and the influence of microstructural evolution on creep behavior is observed. Additionally, the creep life under variable load is predicted based on the linear damage rule (LDR) based on time fraction, the nonlinear damage rule considering the strain history, and the nonlinear damage rule considering the load sequence effect. The results indicate that the creep life and defect quantity of the material are closely related to the overall stress level during variable load creep tests, while changes in the initial stress level have a greater impact on the damage and creep life of the material. The strain variations after load changes include both elastic strain and anelastic strain. Load variations influence dislocation behavior and grain boundary sliding, thereby affecting the creep damage mechanism. The LDR based on the time fraction provide the most ideal prediction results. This study elucidates the creep damage mechanism of 16MND5 steel under variable load conditions and provides a theoretical reference at the material level for the safety maintenance of RPVs under IVR scenarios.</p>

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Influence of variable load history on creep deformation mechanism and life prediction of 16MND5 steel

  • 期刊论文

  • 发表日期：

    2026年7月29日

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  • Qian Xu,
  • Jinchen Cai,
  • Chengwei Zang,
  • Jianfeng Mao,
  • Dasheng Wang,
  • Dongyue Cheng,
  • Mingya Chen

摘要

The lower head of reactor pressure vessel (RPV) will be subjected to high-temperature creep under extreme accident conditions due to the implementation of in-vessel retention (IVR) mitigation measures. In this scenario, the change in internal pressure has a significant impact on the creep behavior of the RPV. Therefore, the paper investigates the creep performance of RPV material 16MND5 steel at 600 and 700 °C under variable load. The effects of load variations on creep rate and lifetime at elevated temperatures are analyzed, and the influence of microstructural evolution on creep behavior is observed. Additionally, the creep life under variable load is predicted based on the linear damage rule (LDR) based on time fraction, the nonlinear damage rule considering the strain history, and the nonlinear damage rule considering the load sequence effect. The results indicate that the creep life and defect quantity of the material are closely related to the overall stress level during variable load creep tests, while changes in the initial stress level have a greater impact on the damage and creep life of the material. The strain variations after load changes include both elastic strain and anelastic strain. Load variations influence dislocation behavior and grain boundary sliding, thereby affecting the creep damage mechanism. The LDR based on the time fraction provide the most ideal prediction results. This study elucidates the creep damage mechanism of 16MND5 steel under variable load conditions and provides a theoretical reference at the material level for the safety maintenance of RPVs under IVR scenarios.