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

Nozawa, Takashi; Snead, Lance Lewis; Katoh, Yutai; Miller, James H.

doi:10.1016/j.jnucmat.2007.05.015

Cited by 15 publications

(6 citation statements)

References 16 publications

(26 reference statements)

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“…Such a similar mechanism for the shape change of silicon carbide has been confirmed by microstructural studies performed using transmission electron microscopy on samples which had been irradiated by neutrons to fluence (4.5-7.7)·10 21 cm -2 (E > 0.1 MeV) at 300-800°C and by silicon ions (E Si 2+~ 5.1 MeV) to 200 displacements/atom [13,14]. It has been shown that point defects and small dislocation loops dominate at relatively low temperatures (≤800°C), while at higher temperatures (1400°C) they grow into Frank loops and, finally, developed into dislocation networks.…”

Section: Of Htgr Fuel Elementsmentioning

confidence: 52%

“…The fact that monolithic cubic silicon carbide retains is strength after neutron irradiation for fluence 2·10 22 cm -2 at 740°C was reported in [7][8][9]. In addition, the data of [10][11][12][13] show that silicon carbide undergoes hardening and/or toughening under neutron irradiation to fluence 10 19 -8·10 21 cm -2 (E > 0.1 MeV) at 800-1050°C. The mechanism of swelling at low irradiation temperature (below 1000°C) is not yet fully understood.…”

Section: Of Htgr Fuel Elementsmentioning

confidence: 83%

“…Using tubular model samples with pyrocarbon and silicon-carbide coatings, the authors of [13] determined experimentally the boundary shear strength with separation of the inner pyrocarbon and silicon carbide to be 240 ± 40 MPa and the boundary friction stress 120 ± 30 MPa. These data indicate that the high boundary strength will make it possible to transfer substantial loads to the inner-pyrocarbon-silicon-carbide interface.…”

Section: Of Htgr Fuel Elementsmentioning

confidence: 99%

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Formation of multifunctional barriers to increase the radiochemical resistance of the protective coatings of HTGR fuel elements

Kurbakov

2009

At Energy

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The radiation-size changes of pyrocarbon protective coatings on HTGR microfuel elements are analyzed. It is shown that there is a relationship between the microstructural inner pyrolytic layers and the formation of cracks in these layers as the irradiation dose accumulates. The effect of cracks in the inner pyrocarbon layers on the damage to the silicon carbide layer is examined. It is determined that incorporating into the inner pyrocarbon layer or forming on the inner pyrocarbon-silicon carbide interface compositions, for example, silicon carbide-carbon, Ti 3 SiC 2 , ZrC, TiC, and nitrides of Zr, Ti, and Al creates an obstacle to interior cracks, increasing the radiation-chemical resistance of the carbide layer and the microfuel as a whole.The structure of the microfuel of high-temperature gas-cooled reactors has evolved from particles with a single-layer protective coating consisting of pyrocarbon with a laminar structure through a bilayer pyrocarbon coating with different density to a fuel microsphere with three layers made of, respectively, inner high-density isotropic pyrocarbon and silicon carbide and an outer layer of high-density isotropic pyrocarbon ( Fig. 1) [1].The specifications for the microsphere fuel for HTGR take account of the following essential characteristics: thickness, density, anisotropy of the pyrocarbon coating, contamination of the coatings by fissile materials, defects in the silicon carbide layer, and others [2-6].The operational parameters (temperature, degree of fuel burnup, fluence of fast neutrons, and others) which have been obtained on the experimental stand satisfied the technical requirements for uranium dioxide microspherical fuel based on multilayer coatings (see Fig. 1, position I) and even exceeded the requirements in individual cases (see Fig. 1, positions II and III).In connection with new problems arising in the development of fourth-generation nuclear-energy systems, the requirements for the operational parameters (nuclear fuel burnup, irradiation temperature, hast-neutron fluence, energy release from a fuel microsphere, and others) are increasing substantially. Probably the biggest problem will be due to the realization of deep burnup of fuel at high irradiation temperature -up to 20% h.a. and higher than 1100°C under stationary operating conditions of a very-high-temperature gas-cooled reactor (VHTR, Japan).One of the variants under consideration variant for improving the performance of multilayer coatings is replacing the silicon carbide load-bearing layer by a zirconium carbide layer. However, such a replacement will make it necessary to solve a multitude of materials-engineering problems, develop methods for monitoring the properties of carbide-zirconium coatings and rejecting microfuel based on them, and determine the capability of zirconium carbide to confine solid fission products at elevated irradiation temperatures taking account of the high neutron fluence for VHTR and GFR (see Fig. 1, positions IV, V).Laboratory investigations performed in the USA on micros...

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Section: Of Htgr Fuel Elementsmentioning

confidence: 52%

Section: Of Htgr Fuel Elementsmentioning

confidence: 83%

Section: Of Htgr Fuel Elementsmentioning

confidence: 99%

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Formation of multifunctional barriers to increase the radiochemical resistance of the protective coatings of HTGR fuel elements

Kurbakov

2009

At Energy

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“…In contrast, Shetty [24] originally discussed the interfacial friction issue for the debonded interface. In the previous work by the authors [25], Shetty's model was updated for anisotropic composites and this method was applied in this study.…”

Section: Single Fiber Push-out Testmentioning

confidence: 99%

“…The detailed analogy of the modified Hsueh model was discussed elsewhere [22,25]. The resultant form can provide an interfacial debond shear strength (s s ) as where the constants k and Z are determined by dimensions and elastic constants of the constituents, and r th and r irr are stress parameters defined by the thermal expansion mismatch and the differential swelling among the fiber, matrix and F/M interphase, respectively (see Appendix).…”

Section: Single Fiber Push-out Testmentioning

confidence: 99%