The core-shell structure silicon-resin precursor powders were synthesized through coat-mix process and addition of Al2O3-SiO2-Y2O3 composite additives.A series of porous silicon carbide ceramics were produced after molding,carbonization and sintering.The phase,morphology,porosity,thermal conductivity,thermal expansion coefficient,and thermal shock resistance were analyzed.The results show that porous silicon carbide ceramics can be produced at low temperature.The grain size of porous silicon carbide ceramic is small,and the thermal conductivity is enhanced significantly.Composite additives also improve the thermal shock resistance of porous ceramics.The bending strength loss rate after 30 times of thermal shock test of the porous ceramics which were added Al2O3-SiO2-Y2O3 and sintered at 1 650 ℃ is only 6.5%.Moreover,the pore inside of the sample is smooth,and the pore size distribution is uniform.Composite additives make little effect on the thermal expansion coefficient of the porous silicon carbide ceramics.
近代低富集度3层包覆颗粒(Modern LEU TRISO Particles)燃料元件的大量辐照试验表明:在高温气冷堆正常运行工况下,燃料元件的包覆燃料颗粒一般不会发生破损,放射性裂变产物的释放主要取决于制造引起的自由铀含量(燃料元件中没有被Sic层完整包覆的燃料颗粒铀量和总铀量之比).燃烧-浸取(Burn-Leach)法可以灵敏、准确地测量自由铀含量.本文介绍了燃烧-浸取法,给出了10MW高温气冷实验堆(HTR-10)首炉燃料元件自由铀含量的测量结果.
