The effect of annealing at 1500°C on migration and release of ion implanted silver in CVD silicon carbide

MacLean, H.J.; Ballinger, R. G.; Kolaya, L.E.; Simonson, S.A.; Lewis, N.; Hanson, M.

doi:10.1016/j.jnucmat.2006.05.043

Cited by 52 publications

(61 citation statements)

References 8 publications

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“…[5], who found at 1500°C a value of D < 5 Â 10 À21 m 2 s À1 . In view of this extremely low limit the diffusion in CVD-SiC can almost entirely be associated with grain boundary diffusion.…”

Section: Discussionmentioning

confidence: 96%

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Study of silver diffusion in silicon carbide

Friedland

Malherbe

Berg

et al. 2009

Journal of Nuclear Materials

106

102

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Section: Discussionmentioning

confidence: 96%

“…However, despite various measurements [4,5] no consistent diffusion coefficients for silver are currently available. Published results differ by orders of magnitude.…”

Section: Introductionmentioning

confidence: 99%

Study of silver diffusion in silicon carbide

Friedland

Malherbe

Berg

et al. 2009

Journal of Nuclear Materials

106

102

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“…Into the coated wafers 360 keV ions were implanted at temperatures ranging from room temperature (RT) to 600 ºC with a fluence of either 2×10 16 Ag + cm -2 or 1×10 16 I + cm -2 and a flux not exceeding 10 13 cm -2 s -1 . High implantation temperatures were chosen to reduce irradiation damage.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Our results are in variance with the findings of ref. [16], who observed no sign of silver migration via either inter-or intra-granular paths.…”

Section: Silver Transportmentioning

confidence: 98%

“…The diffusion coefficients compare quite well, while the activation energy is approximately 20% higher. In view of the extremely low upper limit for the diffusion coefficient in defect-free single crystalline silicon carbide [4,16], the diffusion can almost entirely be associated with grain boundary diffusion. This is also in agreement with an ab initio calculation [17], from which the volume diffusion coefficient for silver at 1300 °C is estimated to be 3.6×10 -33 m 2 s -1 .…”

Section: Silver Transportmentioning

confidence: 99%

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Investigation of silver and iodine transport through silicon carbide layers prepared for nuclear fuel element cladding

Friedland

Berg

Malherbe

et al. 2011

Journal of Nuclear Materials

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Abstract.Transport of silver and iodine through polycrystalline SiC layers produced by PBMR (Pty) Ltd for cladding of TRISO fuel kernels was investigated using Rutherford backscattering analysis and electron microscopy. Fluences of 2×1016 Ag + cm -2 and 1×10 16 I + cm -2 were implanted at room temperature, 350 °C and 600 °C with an energy of 360 keV, producing an atomic density of approximately 1.5% at the projected ranges of about 100 nm. The broadening of the implantation profiles and the loss of diffusors through the front surface during vacuum annealing at temperatures up to 1400 °C was determined. The results for room temperature implantations point to completely different transport mechanisms for silver and iodine in highly disordered silicon carbide. However, similar results are obtained for high temperature implantations, although iodine transport is much stronger influenced by lattice defects than is the case for silver. For both diffusors transport in well annealed samples can be described by Fickian grain boundary diffusion with no abnormal loss through the surface as would be expected from the presence of nano-pores and/or micro-cracks. At 1100 °C diffusion coefficients for silver and iodine are below our detection limit of 10 -21 m 2 s -1 , while they increase into the 10 -20 m 2 s -1 range at 1300 °C.

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Effect of geometry on the stress-strain state of fuel particles with a multilayer coating

et al. 2008

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Interest in high-temperature gas-cooled reactors has increased substantially in recent years. Our country is developing, jointly with the USA, the GT-MGR reactor facility, where a fuel particle is the basic fuel element. Particle-based fuel is one of the most promising variants of nuclear fuel for not only HTGR but also VVER [1]. The main feature of HTGR particle-based fuel is the possibility of attaining high coolant (helium) temperature up to 1000°C at the exit from the core with a high degree of confinement of fission products, which is achieved by, first and foremost, maintaining the airtightness of the protective coatings. As a result, theoretical-computational modeling of the behavior and prediction of the fraction of particles whose coating has sustained through damage during irradiation plays a role. Computational modeling makes it possible to work out a structure, choose the main parameters, predict the serviceability of fuel particles, and develop the optimal plan for reactor studies at lower cost.A fuel particle consists of a fuel kernel surrounded by coating layers consisting of pyrocarbon and silicon carbide (Fig. 1).Tens of computational codes have been developed to simulate the behavior and predict the serviceability of a fuel particle [2][3][4][5][6]. In most of these codes, it is assumed that a fuel particle possesses a perfectly symmetric shape, which greatly simplifies the problem. Correspondingly, one-dimensional codes are fast, which makes it possible to take account of a larger number of physical and chemical processes occurring as fuel burns as well as the statistical character of different parameters affecting the lifetime of the fuel.However, codes in this class cannot take account of possible deviations of the shape of real fuel particles from an ideal sphere. Shape distortions can arise during the fabrication of the particles as well as during reactor operation. Figure 2 shows a radiophotograph of fuel particles with typical shape deviation in the form of faceting arising at the time the coatings are deposited.Under irradiation, fission products accumulate in the fuel particles. Some fission products, for example, palladium, chemically interact with the silicon carbide coating. The chemical interaction between silicon carbide and the fission products and CO, which is formed as fuel burns up, can be local, which is often observed in studies of irradiated fuel.Aside from local corrosion, phenomena such as partial separation of the coating, crack formation in individual layers of the coating, and displacement of the kernel relative to the center of a fuel particle (amoeba effect) can also be observed. The development of models and computer codes for describing such phenomena and evaluating their effect on the serviceability of fuel particles has started only in the last few years. Examples of such codes are PARFUME [2, 3] and ATLAS [4], which employ the finite-element method.The objective of the present work was to evaluate the effect of different types of asphericity on the strength of th...

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The effect of annealing at 1500°C on migration and release of ion implanted silver in CVD silicon carbide

Cited by 52 publications

References 8 publications

Study of silver diffusion in silicon carbide

Study of silver diffusion in silicon carbide

Investigation of silver and iodine transport through silicon carbide layers prepared for nuclear fuel element cladding

Effect of geometry on the stress-strain state of fuel particles with a multilayer coating

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