The fracture strength of TRISO-coated particles determined by compression testing between soft aluminium anvils

Abstract

Abstract:Compression testing of tri-isotropic (TRISO) carbon/silicon carbide-coated fuel particles between anvil materials with a wide range of hardnesses was investigated. During compression testing, the particle produces a hardness impression before it fractures. For subsequent measurements, the same position can therefore not be used.A special testing machine was designed to use the same set of anvils for testing more than one specimen. By each time positioning a particle at a slightly different position between the anvils, a large number of measurements could be made. The load required for fracture is almost independent of anvil hardness for very hard or very soft anvils. Finite element stress analysis showed that when the anvil hardness is very high, fracture occurs because of high local contact bending stresses at the point of contact.In the case of very soft anvils, a tensile stress develops along a latitudinal direction along the perimeter of the particle over a large volume in between the contact zones with the anvils. The particle then fractures by the development of cracks at right angles to the direction of the tensile stress. From the fracture load, the ability of the particle to withstand internal pressure can be assessed. The advantages of using compression testing of full particles between soft anvils without prior preparation to complement previous test methods are highlighted.

Diffusion of fission products and radiation damage in SiC

“…The SiC layer, however, has a number of other important functions. For example, it also provides mechanical support and structural rigidity to the coated particle [83,84] even under conditions of thermal shocks [85] which occurs during the operation of a pebble bed modular reactor. This means that there must be strong bonding between the SiC layers and its two neighbouring PyC layers as discussed earlier.…”

“…The initial oxidation of Si-rich 3C-SiC(100) (3×2) surface (and also the 6H-SiC(0001)-(3×3) and the 4H-SiC(0001)-(3×3) reconstructed surfaces [88 -91]) shows a very high reactivity rate -approximately three orders of magnitude above those of silicon surfaces [87,92,93]. The other Siterminated reconstructed surface of 3C-SiC and also the other hexagonal SiC polytypes and their surfaces [89] require high oxygen exposures and high temperatures for oxide formation [83].…”

The influence of annealing temperature on the strength of TRISO coated particles

“…The fracture strength was determined by the recently developed method by Van Rooyen et al [9] by compressing the CPs between soft anvils. Finite Element Analysis (FEA) modelling was used to quantify the stress to which the particle was subjected [9].…”

“…The fracture strength was determined by the recently developed method by Van Rooyen et al [9] by compressing the CPs between soft anvils. Finite Element Analysis (FEA) modelling was used to quantify the stress to which the particle was subjected [9]. The results by Van Rooyen et al [9] showed that the removal of the outer layer of PyC by decarburization, still gave results comparable with the results obtained with the O-PyC layer intact.…”

“…Finite Element Analysis (FEA) modelling was used to quantify the stress to which the particle was subjected [9]. The results by Van Rooyen et al [9] showed that the removal of the outer layer of PyC by decarburization, still gave results comparable with the results obtained with the O-PyC layer intact. Therefore it was decided to do the strength measurements for this study with the O-PyC layer intact, in other words, the CP with all three layers intact was measured, eliminating artificial contributions due to sample preparation.…”