Abstract: Uranium dioxide is the main nuclear fuel used in nuclear power plants. It has the advantages of high melting point, high radiation resistance and good compatibility with cladding and coolant. However, the thermal conductivity of UO2 fuel is low, and when the reactor burnup is deep, the fuel is prone to swell, which leads to the mechanical and chemical interaction (PCMI) between fuel and cladding, which increases the safety risk of the reactor, improving the thermal conductivity of UO2 fuel is the key direction of the future research on the modification of high performance nuclear fuel. Graphene has the advantages of high melting point, high thermal conductivity and high temperature stability. It is a valuable second-phase additive in UO2 fuel pellets. However, at present, the general process of graphene doping is physical mixing, so it is difficult to solve the problem of mixing uniformity between graphene and high density ceramic materials, which limits its doping performance. In this paper, a kind of nucleation method based on graphene and in situ synthesis of uranyl nitrate solution and ammonia water on nucleation was used, by controlling the reaction parameters, UO2-graphene composite fuel powders doped with 2vol%,4vol%,6vol% and 8vol% graphene were prepared, composite fuel pellets were prepared by spark plasma sintering (SPS). The process mechanism and fuel properties were investigated. The results show that the uniformity of UO2-graphene powder prepared by in situ synthesis method is up to 96.39%; The analysis of phase structure show that only UO2 and graphene exist in the sintered pellets at 1 450 ℃, the graphene is not destroyed by reacting with UO2; the density of in situ synthesis pellets doped with 2vol%,4vol%,6vol% and 8vol% graphene are 95.56% TD, 95.32% TD, 95.08% TD and 94.76% TD respectively; the thermal conductivity of pellet at 20 ℃ increase by 12.27%, 20.13%, 27.47% and 34.13% respectively, the thermal conductivity of pellet at 1 000 ℃ increase by 18.36%, 35.00%, 47.07% and 58.93% respectively, graphene has better performance in the high temperature ser-vice stage of fuel, which makes up for the disadvantage of lower thermal conductivity of UO2 at high temperature. The results of SEM show that the grain size of the pellet prepared by in-situ synthesis method is 10~ 30 μm, there is no obvious pore at the grain boundary, graphene is uniformly coated by UO2, the thermal conductivity of the pellet is improved by forming a bridging heat conduction network.
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2020, Vol. 34 
