Nuclear Power is a clean and efficient electricity generation method that plays a crucial role in meeting national energy demands, optimizing the energy structure, ensuring energy security, and promoting sustainable economic development. It also serves as an effective means to reduce environmental pollution and achieve economic ecological development. In recent years, China has experienced rapid growth in nuclear power development, with a 6.6% increase in annual cumulative electricity generation compared to the previous year.
However, the development and utilization of nuclear power come with significant social and economic benefits as well as safety challenges. Following the Fukushima nuclear accident, South Korea placed a high emphasis on nuclear safety. One critical issue in nuclear power utilization is the handling of high-level radioactive waste, which is a key factor for sustainable nuclear energy production.
The internationally recognized and most reasonable method for managing radioactive waste involves geological disposal of solidified radioactive waste, ensuring the long-term separation of high-level waste from the human living environment to minimize or eliminate its impact on nature and humans.
High-level waste storage tanks are specialized containers for storing solidified high-level waste. The glass solidification of high-level waste is a well-established treatment method that has been applied in practical engineering for over 30 years and is mature in its technology. It has been widely used in developed countries such as France, the UK, the US, and Japan, while China is still in the experimental research stage, with storage tanks made from 310S austenitic stainless steel.
During the actual welding of the tank body, it was observed that there were severe rough grains in the Coarse-Grained Heat-Affected Zone (CGHAZ) of the welding area. This led to a reduction in the impact toughness of the 310S austenitic stainless steel CGHAZ, a decrease in crack propagation resistance, and an increase in brittle transition temperature. Stress concentration is also likely to occur, particularly when grain size is uneven, which can restrict the use and application of the austenitic stainless steel.
Currently, there are three main methods to inhibit grain growth in the weld heat-affected zone in practical industrial applications. The first method is to adjust the welding process, which involves reducing welding current and increasing welding speed to decrease the grain size in the weld heat-affected zone. However, this significantly reduces welding quality and efficiency.
The second method is phase transformation, where heat treatment is applied to induce a phase change in the weld heat-affected zone, resulting in smaller grains. Because 310S austenitic stainless steel maintains a fully austenitic structure from room temperature to the solid phase, phase transformation cannot be used to adjust its structure.
The third method involves adding alloy elements to the base material, causing the second phase particles and fine grains to precipitate at the interface, which serves to immobilize grain boundaries and hinder their movement. This method has strong applicability and a noticeable inhibitory effect.
310S austenitic stainless steel, with 25% Cr and a maximum of 20% Ni, is a high-chromium, nickel-based fully austenitic stainless steel that retains corrosion resistance and mechanical performance. Therefore, waste storage tanks primarily use 310S austenitic stainless steel. Currently, domestic Baosteel Group and Taiyuan Iron and Steel Group mainly produce 310S steel under the grade 06Cr25Ni20, with American ASTM and UNS standards designating it as 310S and S31008, respectively. In South Korea, the KS standard grade is STS310S, while in the EU, it is labeled as BSEM 1.4845, and in Australia, it is known as AS standard grade.
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