Modeling Method and Impact Analysis of Fuel Rod Radial Thermal Expansion of PWR

During the power operation of PWR, fuel pellets and cladding undergo varying degrees of thermal expansion due to temperature changes, which significantly impacts the core physics calculations. In order to accurately consider the influence of fuel rod radial thermal expansion on the core physics analysis results in the "two-step" scheme, this paper proposes a precise modeling method for fuel rod radial thermal expansion based on the reactor-physics analysis software Bamboo-C. This method considers the geometric changes caused by fuel rod radial thermal expansion at both the assembly calculation and reactor core calculation levels, and determines the precise geometric expansion size through iterative convergence of the temperature field at the core calculation level. In this paper, the EPR1750 unit is taken as the research object, and the startup physical tests and power operation processes of each fuel cycle are calculated. The results show that: the average error between the calculated and measured isothermal temperature coefficients decreased from −3.065 pcm/K (1pcm=10^–5) to −1.870 pcm/K, and the average error between the calculated and measured critical boron concentrations decreased from −5.9ppm (1ppm=10^–6) and −5.7ppm to −2.5ppm and −2.7ppm. Therefore, the PWR fuel rod thermal expansion modeling method proposed in this paper can improve the calculation accuracy of key safety parameters of EPR1750 to a certain extent and has certain engineering application value.