Evaluation of the Fracture Strength for Silicon Carbide Layers in the Tri‐Isotropic‐Coated Fuel Particle

Abstract

A program to develop new methods to measure the fracture strength of the chemical vapor deposition SiC coatings in nuclear fuel particles has been carried out. Internal pressurization and crush test techniques were developed and applied to prototype‐sized tubular and hemispherical shell specimens. The fracture strength measured from each test method applying the Weibull two‐parameter distribution, and Weibull parameters were measured. It was shown that data generated with each test technique were independent of the test technique applied. This implies that the developed test methods are reliable and provide reasonable strength data. For the same material, fracture strength varied with the specimen geometry and loading configuration. These size and loading configuration effects on the fracture strength are explained with the concept of effective surface.

Handbook of SiC properties for fuel performance modeling

“…Two key parameters: the Weibull modulus, m, and the Weibull characteristic strength, r 0 , have been determined for b-SiC by various test techniques (Table 7). It is noted that the extremely high Ni ihara, MI [117] Ni ihara, DT [117] Ni ihara, SENB [117] Ni ihara, DCB [117] Rohm and Haas Co., MI [32] Rohm and Haas Co., SCF [ characteristic strength obtained by O-ring compression or hemispherical bend tests is likely due to inadequate analytical procedures and/or extremely tiny fracture volume, as pointed out by Hong et al [148]. It is recommended that the circumferential tensile strength of spherical coatings is best determined using test methods such as internal pressurization which applies uniform loading over the entire sample surface.…”

Effect of coating temperature on properties of the SiC layer in TRISO-coated particles

“…The effective surface area was calculated from the tensile stress distribution at the inner surface of the shell specimen in the FE analysis by assuming a point contact between the SiC shell and upper alumina rod. As pointed out by Hong et al [12], however, there is a significant surface roughness-induced flattening at the contact between the shell and upper loading block. The contact flattening has large influence on the effective surface and thus on the determination of fracture stress.…”

“…The fracture stress of the SiC layer was measured through a crush test of a hemispherical shell specimen which was a similar configuration to the report by Hong et al [12]. The TRISO-coated particles mounted in an epoxy resin were ground close to the equatorial plane of the particles and the SiC hemispherical shell specimens were collected after burning off the IPyC and OPyC layers.…”

Shear properties at the PyC/SiC interface of a TRISO-coating

“…On the other hand, the hoop strength of SiC, which was measured by the internal pressurization technique for thin-walled miniature tube specimens, is 310-450 MPa [17]. Considering the effect of specimen size [18], the hoop strength of the SiC layer of the model TRISO-coated tube is more than 580 MPa. Therefore, the failure of a SiC layer by internal pressurization seems unlikely.…”