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制粒工艺参数对MOX燃料粉末性能的影响

Effects of granulation process parameters on properties of MOX fuel powders

  • 摘要: 为减少粉尘飞扬,提高铀钚混合氧化物燃料(MOX燃料)混合粉末的流动性能,降低废品率,利用Al2O3粉末模拟MOX燃料粉末,系统性开展干法制粒一体工艺技术研究,通过金相显微镜、扫描电镜及筛分分析法探讨轧制压力、制粒次数、压辊间隙及球化时间对粉末松装密度、制粒率的影响。结果表明,随着轧制压力由2 kN·cm‒1增大至18 kN·cm‒1,粉末松装密度逐渐增加(由0.752±0.002 g·cm‒3增大至0.813±0.002 g·cm‒3),而制粒率(质量分数)呈现先增后降趋势,其峰值达(87.5±0.3)%;当压力超过10 kN·cm‒1时,颗粒内部裂纹缺陷数量显著上升。当制粒次数从1次增至6次时,粉末松装密度持续上升,制粒4次后,制粒过程趋于稳定。压辊间隙增大导致松装密度先升后降,其间隙优选1.0~2.0 mm,制粒率呈递减趋势。延长球化时间可使松装密度渐增并趋稳,球化时间2.0 h较优,可获得高松装密度(0.815±0.004 g·cm‒3)的类球形颗粒,有效改善压制填充性能。

     

    Abstract: To reduce the dust dispersion, improve the flowability of uranium plutonium mixed oxide fuel (MOX fuel) powders, and decrease the production scrap rate, the Al2O3 powders were used to simulate the MOX fuel powders, and the dry-granulation integrated technology of MOX fuel powders was systematically studied. The influence of rolling pressure, granulation time, rolling gap, and spheroidization time on the bulk packing density and granulation rate of the MOX fuel powders was investigated by metallographic microscopy, scanning electron microscopy, and screening analysis methods. The results show that with the rolling pressure increasing from 2 kN·cm‒1 to 18 kN·cm‒1, the bulk packing density gradually increases from 0.752±0.002 g·cm‒3 to 0.813±0.002 g·cm‒3, and the granulation rate (mass fraction) shows a trend of increasing first and then decreasing, with a peak of (87.50±0.30)%. The number of crack defects inside the particles increases significantly when the pressure exceeds 10 kN·cm‒1. When the granulation time increases from 1 to 6, the bulk packing density continues to rise, but the granulation rate shows the characteristics of rising first and stabilizing. After 4 times of granulations, the powder proportion (mass fraction) above 150 mesh reaches (84.10±0.15)%, but after 6 times of granulations, it only rises to (84.50±0.12)%, indicating that the granulation process tends to be stable after 4 times of granulation. The increase of rolling gap causes the bulk packing density to rise first and then fall, with a peak value of 0.738±0.002 g·cm‒3, meanwhile, the granulation rate continues to decline. As the spheroidization time extends, the bulk packing density gradually increases and tends to be stable, the particle shape also changes from irregular to spherical. To sum up, the spherical particles with high bulk packing density (0.815±0.004 g·cm‒3) can be stably obtained when the dry granulation process parameters are comprehensively regulated as: the rolling pressure should be inferior to 10 kN·cm‒1 to suppress the particle cracks, the effective granulation saturates at 4 times, the rolling gap is best to be within 1.0~2.0 mm, and the optimal spheroidization time is 2.0 h, which can effectively improve the compression and filling performance of MOX fuel powders, and provide a key technical support for the engineering application of MOX fuels.

     

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