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Accident tolerant fuel can improve the safety of nuclear reactor core and strengthen the ability of nuclear reactor to withstand serious accidents. Coated particle dispersed fuel has become a hot research topic in accident tolerant fuel in recent years, due to its high thermal conductivity and good radiation resistance stability. Coated particle dispersed fuel consists of threedimensional isotropic coated particles as the fuel phase and silicon carbide as the matrix phase, adopting the fuel form of coated particle dispersed in the silicon carbide matrix. However, due to the low selfdiffusion rate of SiC, it is difficult to achieve high densification by solid phase sintering, which is only controlled by diffusion. The existing sintering process mainly involves adding sintering aids or generating liquid glass phase to assist in the sintering of SiC powder. Spark plasma sintering (SPS) process can activate powder particles and promote sintering, and has been widely used in nuclear ceramic sintering in recent years. This article used SPS to prepare coated particle dispersed fuel pellets, and studied the influence of sintering process parameters on the density of the coated particle dispersed fuel pellets, such as the amount of sintering additive addition, maximum sintering temperature, maximum sintering pressure, and holding time. It is found that the best process parameters for SPS sintering of coated particle dispersed fuel pellet is 7% of sintering additive addition, holding 15 minutes at 1 850 ℃ and 45 MPa. Under such process parameter, the relative density of pellet can reach 98.5% of theoretical density. In addition, the sintering mechanism of coated particle dispersed fuel was studied and it is found that the sintering of coated particle dispersed fuel can be divided into five stages. Phase detection, metallographic detection and microstructure characterization analysis of the coated particle dispersed fuel pellets were carried out. The XRD examination results indicate that after sintering, the coated particle dispersed fuel pellet is pure β phase, which indicate that SPS rapid sintering can better control the phase transition. The metallographic examination results indicate that there is no obvious contact between TRISO particles in the coated particle dispersed fuel pellet obtained under the optimal process conditions. The SEM examination results show that the overall integrity of TRISO particles is good, indicating that the structure of TRISO particles dose not break during the sintering process. In the thermal shock test, there are no penetrating micro-cracks on the surface of the fuel pellet after a thermal shock, which maintain good integrity.

Application of the AUSMV (advection upstream splitting method V) scheme was extended from gas dynamics to transient ID isothermal gas-liquid two-phase pipe flow problems. The method of numerical flux for the DFM (drift flux model) constructed with the AUSMV scheme and treatment of boundary cells were stated for the simulations. The numerical calculation method of 2nd-order accuracy in time and space was obtained with the classical Runge-Kutta method and the monotonous MUSCL (monotone upstream-centred schemes for conservation laws) technique combined with the Van Leer limiter. The numerical examples including the Zuber-Findlay shock tube problem and the variable mass flow problems with complex slip relations were conducted and comparatively discussed. The results indicate that the proposed AUSMV scheme, with advantages of high efficiency, high precision and low effects of dissipation and dispersion, accurately details the discontinuities of ID gas-liquid two-phase flow problems under low flow velocity conditions. [ABSTRACT FROM AUTHOR]

Application of the AUSMV (advection upstream splitting method V) scheme was extended from gas dynamics to transient 1D isothermal gas-liquid two-phase pipe flow problems. The method of numerical flux for the DFM (drift flux model) constructed with the AUSMV scheme and treatment of boundary cells were stated for the simulations. The numerical calculation method of 2nd-order accuracy in time and space was obtained with the classical Runge-Kutta method and the monotonous MUSCL (monotone upstream-centred schemes for conservation laws) technique combined with the Van Leer limiter. The numerical examples including the Zuber-Findlay shock tube problem and the variable mass flow problems with complex slip relations were conducted and comparatively discussed. The results indicate that the proposed AUSMV scheme, with advantages of high efficiency, high precision and low effects of dissipation and dispersion, accurately details the discontinuities of 1D gas-liquid two-phase flow problems under low flow velocity conditions. [ABSTRACT FROM AUTHOR]