Analysis of Particle Agglomeration Effect on Failure of Dispersion Nuclear Fuel Meat

Abstract

By dispersing the fuel particles in an inert metal matrix, the dispersion nuclear fuel element has the advantages of high burnup, high thermal conductivity, great safety and strong designability, etc. It has been successfully applied in the test reactors. Within a dispersion nuclear fuel element, the failure of fuel meat is significantly influenced by the particle agglomeration behavior, including the agglomeration extent, the location of agglomeration region, fuel particle spacing, etc. The present study investigates the crucial factors influencing the failure behavior in the dispersion nuclear fuel meat, focusing on the particle agglomeration effect on the failure of fuel meat. By developing a script for parametric modeling and numerical calculations of the representative volume element in the dispersion nuclear fuel element, the Mises stress field of dispersion nuclear fuel meat incorporating with different particle agglomeration characteristics was simulated in this paper. Numerical modeling was performed by considering the damage layer at the fuel-matrix interface, irradiation-induced fuel particles swelling and the environmental pressure outside the cladding. The effects of particle agglomeration volume fraction, location of the agglomerate fuel particles, ambient hydro-static pressure and matrix material properties on the failure of dispersion nuclear fuel meat were analyzed systematically. The fuel particles in agglomeration region were geometrically modeled through dense stacking, while the local particle agglomeration volume fraction was defined by the minimum particle spacing. The results show that the failure behavior in dispersion nuclear fuel meat is enhanced with the increasing of particle agglomeration volume fraction. The environmental pressure outside the cladding can inhibit the stress concentration in the dispersion fuel meat, but this influence declines with the extent of local fuel agglomeration increasing. Furthermore, the particle agglomeration location between the upper and lower cladding layers of the thin plate indicates little effect on the maximum Mises stress in the dispersion nuclear fuel meat. However, compared to the dispersion meat adjacent to the surrounding cladding, fuel particles agglomerating in central meat (i.e. only constrained by the upper and lower cladding) are more sensitive to environmental pressure. The local fuel particle agglomeration has a shortest stave effect on the failure of dispersion nuclear fuel meat. The volume fraction of agglomeration will seriously exacerbate the stress concentration, and the agglomeration location in the interior of dispersion fuel meat will fail first. Therefore, it is concluded that the extent of fuel particle agglomeration, the location of agglomeration region within the dispersion nuclear fuel meat, and the environmental pressure are crucial factors influencing the failure behavior of fuel meat. The fuel particle agglomeration region is the onset location for the local macroscopic failure, and the environmental pressure outside the cladding can decrease the plastic stress concentration in the dispersion fuel meat to improve the safety of reactor core. This work provides an analytical approach and numerical reference for the failure condition prediction, the reliability evaluation, and the structural optimization design of the plate dispersion nuclear fuel element.

Keywords

• dispersion nuclear fuel element
• particle agglomeration
• strength analysis
• shortest stave effect
• matrix failure