Jialong Yuan

The operation of floating nuclear power plants is subject to a number of environmental factors in addition to the typical working temperature and pressure loads. These include marine environmental loads, which can cause fatigue damage and therefore must be taken into account. The fatigue analysis of marine structures frequently employs frequency domain methods, whereas the fatigue analysis of pressure equipment predominantly utilizes time-domain methods. At present, there is no comprehensive and accessible approach for conducting a fatigue analysis of pressure equipment in floating nuclear power plants. In light of the aforementioned considerations, this paper puts forth a novel approach to evaluating fatigue damage based on the principle of damage combination. This article presents a finite element model of pressure equipment and a methodology for calculating the transfer function of such equipment under wave loads. The frequency domain method is employed to calculate the fatigue damage caused by wave loads, with consideration given to both the working temperature and pressure load. The stress time history curve of pressure-bearing equipment is then calculated using the time-domain method. Subsequently, the fatigue damage caused by thermal pressure loads is obtained through a combination of the rainflow counting method and cumulative damage theory, with verification conducted using time-domain calculations. In comparison to alternative damage combination methodologies, the novel approach offers more precise and straightforward damage calculations, with promising potential for integration into engineering design.

Nuclear power technology has rapidly advanced with the growing global demand for clean energy. As one of the core components of nuclear power plants (NPPs), the design and lifespan evaluation of reactor pressure vessels (RPVs) are critically important. However, while fatigue analysis methods for RPVs in land-based NPPs are relatively well established, the application of these methods to floating nuclear power plants (FNPPs) faces great challenges. Existing analysis methods are difficult to directly apply, and no widely accepted fatigue analysis approach currently exists for this context due to the complex working conditions in marine environments. A time-domain design stress (TDDS) method is developed in this study for the fatigue analysis of RPVs in FNPPs. This method systematically analyzes the impacts of wave loads, internal pressure, and thermal effects on the fatigue life of RPVs by simplifying the wave environment into a time-domain model of roll and pitch motions and adopting the regular wave superposition techniques. This method further adjusts the initial phases of regular waves considering the uncertainty of various load combinations, and superimposes the stress components caused by regular waves with different initial phases, thermal loads, and pressure loads. Subsequently, stress history curves are analyzed using the rainflow counting method, and combined with the damage accumulation theory, the upper and lower limits of fatigue damage are obtained. The results demonstrate that compared to traditional methods in time-domain analysis, the proposed TDDS method provides greater accuracy in evaluating the fatigue life of RPVs in FNPPs, with the average error in fatigue damage values being only 0.033%. Furthermore, the TDDS method reduces analysis time by approximately 70%, which significantly improves computational performance. These findings underscore the reliability and effectiveness of this method in practical applications.