Extending the service life of nuclear power plant components beyond their originally designed operational period requires a detailed understanding of the microstructural stability of the materials used. This study focuses on low-temperature precipitation in the austenitic stainless steel 08CH18N10T, which is employed in the main circulation piping of pressurized water reactors. During long-term operation in the temperature range of 100–320 °C, secondary phases such as M₂₃C₆ carbides and intermetallic phase sigma (σ) can precipitate, which can lead to local chromium depletion at grain boundaries, subsequent sensitization of the steel, and susceptibility to intergranular corrosion. The research includes the analysis of samples taken from the decommissioned V1 unit of the Jaslovské Bohunice Nuclear Power Plant, which has been in operation for 28 years. The samples were subjected to thermal aging under laboratory conditions, with an emphasis on evaluating microstructural changes and their impact on corrosion resistance. Based on the experimental results, it can be concluded that the thermal stability of all tested materials is suitable for the operation of the main circulation piping, as the service temperatures to which the main circulation piping is exposed during operation remain below the activation of precipitation that would lead to sensitization and, consequently, susceptibility to intergranular corrosion. Activation of low-temperature precipitation was observed only at 450 °C, while at temperatures up to 400 °C, the structural stability of the material was confirmed, demonstrating its suitability for operation within the specified temperature range of the nuclear power plants’ main circulation piping.