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球床型氟盐冷却高温堆(Pebble-bed Fluoride-salt-cooled High-temperature Reactor,PB-FHR)是下一代核反应堆堆型之一,它融合了高温气冷堆的石墨基质包覆颗粒燃料球技术和熔盐堆的高温熔盐冷却剂技术。堆芯热工水力模拟计算(如在线换料模拟)常需要首先得到不同孔隙率的随机燃料球堆积。为此提出了一种可以高效地在圆柱形容器内部随机生成单一粒径且不同密实度的颗粒堆积的算法。算法分为两个阶段:首先类似传统颗粒自由下落方法来生成柔性颗粒的初始堆积(取颗粒杨氏模量远小于实际值);其次令初始堆积恢复刚性,通过限定时间步的大小和引入能量耗散机制使得堆积缓慢而自由地膨胀,从而逐渐消除初始堆积中的颗粒间重合。模拟结果表明,膨胀算法在计算效率上有较大优势,并且可以覆盖从松散到密实的堆积范围。通过控制自由下落阶段的杨氏模量、摩擦系数、缓慢膨胀阶段的摩擦系数这三个变量来控制堆积的孔隙率和计算效率。
The Pebble-bed Fluoride-salt-cooled High-temperature Reactor (PB-FHR) is one of the next generation nuclear reactors. It incorporates graphite substrate coated pellets Technology and Molten Salt Reactor Molten Salt Coolant Technology. Core thermal hydraulic simulation (such as online refueling simulation) often need to get random porosity of different random ball accumulation. To this end, an algorithm is proposed to efficiently generate particles of different particle sizes and different densities in a cylindrical vessel. The algorithm is divided into two stages: first, similar to the traditional free fall of particles, the initial accumulation of flexible particles (taking the Young’s modulus of the particles much smaller than the actual value); secondly, the initial accumulation is restored to rigidity by limiting the size of the time step and introducing energy Dissipation mechanism makes the accumulation of slow and free expansion, thereby gradually eliminate the initial accumulation of particles in the overlap. The simulation results show that the expansion algorithm has greater computational efficiency and can cover the range from loose to dense accumulation. By controlling the three parameters of the Young’s modulus, the friction coefficient and the coefficient of friction during the slow phase of expansion, the accumulated porosity and the calculated efficiency are controlled.