Aging Issues and Mitigation Strategies of Disposable and Pre-embedded Metal Storage Tanks in Nuclear Power Plants

The pre-embedded metal storage tanks in nuclear power plants are widely used in nuclear power plants to provide water sources for safe injection into the reactor under accident conditions or to supply desalinated water, sealing water, treated water, or lubricating oil to the nuclear island, conventional island, and BOP equipment, as well as for collecting radioactive waste liquids and gases. Leakage incidents caused by aging issues of pre-embedded metal storage tanks in nuclear power plants have occurred at home and abroad, impacting the safe and stable operation of the power plant. The pre-embedded metal storage tanks in nuclear power plants are typically large in volume, with some located in basements or partially buried in concrete, making management challenging and replacement difficult or impossible during the service life. The types, uses, storage media, and operating environments of the pre-embedded metal storage tanks in nuclear power plants are diverse, with variations in aging effects and mechanisms. Due to the simplicity and predictability of uniform corrosion mechanisms, significant researches were conducted internationally on component design, aging prevention, and lifetime prediction, leading to the establishment of relevant standards. Corrosion and cracking issues caused by local harsh environments typically manifest as rapid defect expansion rates and difficulties in inspection. Therefore, such aging issues are often critical factors affecting the service life of the pre-embedded metal storage tanks, yet a systematic aging management approach is currently lacking for the pre-embedded metal storage tanks in nuclear power plants. Through in-depth investigation and research on aging issues of the pre-embedded metal storage tanks at home and abroad, stress corrosion cracking, pitting, and crevice corrosion were clearly identified as the three main aging mechanisms threatening the safe operation of the tanks in this paper. Corresponding to these three aging mechanisms, analysis and research on aspects such as appearance, influencing factors, preventive measures, and inspection methods were conducted in this paper. To ensure the safe and reliable operation of the pre-embedded metal storage tanks in nuclear power plants, the research focused on six key dimensions: assessing the current situation, identifying influence factors, determining aging mechanisms, collecting indicative data and assessing potential consequences, and formulating effective a