Stress State and Key Influencing Factor in High Burnup Nuclear Fuel Particle

Abstract

Advanced nuclear reactors are currently moving toward longer fuel cycles and higher burnup levels. Besides, high burnup levels can improve fuel economy and reduce the total amount of spent fuel in reactors. The formation of high burnup fuel particle is closely related to the failure behavior of ceramic dispersion fuel, and it is of great significance to focus on the strength analysis and cracking behavior of high burnup fuel particle. The representative volume element of dispersion fuel was innovatively established in this paper, and the heterogeneity of pore size and position in high burnup fuel particle was considered, corresponding parametric modeling and mechanical simulation procedure of high burnup fuel particle was realized automatically. The impacts of mechanical property of matrix, distance between fuel particles, ambient hydrostatic pressure and damaged layer on the strength of the fuel particles were analyzed systematically. The results show that the distance between fuel particles increases, the less possibility of crack initiates from the fuel particle. The existence of damaged layer will increase the risk of cracking of the fuel particles slightly. Due to the stress interference of the heterogeneous pores, crack initiates from multiple sites within the fuel particle, and the danger zones are more possibility located at the outer space, which is consistent with the experimental observations. Besides, danger zones within the high burnup fuel particle were characterized by larger pores and pore strings. It can be inferred that the formation of larger pores is probably due to the continuous coalescence of small pores and their surrounding pores. The constraint pressure of matrix on the fuel particle is not a constant, specially, it fluctuates significantly, and its average value increases linearly with the ambient hydrostatic pressure. Increasing the elasticity modulus of the matrix will inhibit the cracking behavior of the fuel particle, which reveals that the matrix should be designed more stronger and tougher. The higher the ambient hydrostatic pressure, the less likely the fuel particle will crack. While shortening the distance between fuel particles, and the impact degree of ambient hydrostatic pressure reduces. This work realizes the accurate calculation of the internal stress field of high burnup fuel particle and establishes a high burnup fuel cracking strength evaluation model based on fine microstructure modeling. Besides, this paper provides an analytical method and numerical reference for the failure study and optimal design of dispersion fuel under high burnup conditions.

Keywords

• dispersion fuel
• high burnup fuel particle
• matrix
• constraint effect
• hydro-static pressure
• cracking behavior