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在球形燃料元件中,包覆颗粒的填充因子低于10%,分布具有很大的随机性。本文利用MATLAB程序实现了4种填充的建模方式,即体积等效规则填充、扰动的规则填充、随机的规则填充和完全随机填充模拟燃料球中包覆颗粒的分布。基于固态燃料钍基熔盐堆(Thorium-based Molten Salt Reactor with Solid Fuel,TMSR-SF1)设计中选用的包覆颗粒燃料参数,使用蒙特卡罗程序MCNP6 1.0和ENDF/B VII.0数据库进行了全反射边界条件下的单燃料球临界计算,精确量化了不同的建模方式引起的中子物理特性参数的差异。计算表明,这4种建模方式形成了不同的包覆颗粒聚集程度。包覆颗粒的聚集会导致丹可夫效应的增强,从而增大了中子被燃料吸收的概率,无限增殖因数随之增大,燃料温度系数随之减小。
In spherical fuel elements, the fill factor of the coated particles is less than 10% and the distribution is highly random. In this paper, we use MATLAB program to achieve four kinds of filling modeling methods, namely volume-equivalent rule filling, rule-filling disturbance, random rule filling and completely random filling simulation of the distribution of fuel particles in the ball. The parameters of the coated particulate fuel used in the design of the Thorium-based Molten Salt Reactor with Solid Fuel (TMSR-SF1) were determined using the Monte Carlo program MCNP6 1.0 and ENDF / B VII.0 databases The critical calculation of single fuel spheres under total reflection boundary conditions accurately quantifies the difference of neutron physics parameters caused by different modeling methods. Calculations show that these four kinds of modeling methods form different degree of aggregation of coated particles. The agglomeration of the coated particles leads to the enhancement of the Dankoff effect, which increases the probability of neutron absorption by the fuel. As a result, the infinite multiplication factor increases and the temperature coefficient of the fuel decreases.