球形燃料元件中包覆颗粒的分布效应研究

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。

Effect of TRISO-particles distributions in pebble fuel

Background: Packing fraction of tristructural-isotropic (TRISO) particles in pebble fuel is lower than 10% in general, which leads to great randomness in distribution, resulting in various challenges in neutronics modeling, such as double heterogeneity effect, preserving exact number of particles, and their random distributions in pebble.Purpose: This study aims to verify the calculations, the infinite pebble fuel with refectory boundary conditions based on the thorium-based molten salt reactor with solid fuel (TMSR-SF1) pebble design using Monte-Carlo code MCNP6 ver1.0 and ENDF/B VII.0.Methods:Four types of models of TRISO particles have been performed based on MATLAB, the equivalently filled regular model, the disturbed regular model, the randomly filled regular model, and the fully random model.Results: The neutronic effect of various modeling approaches was quantitatively evaluated.Conclusion:The results show that the four kinds of modeling methods form different randomness. The clustering of the coated particles enhances the Dancof effect which raises the neutron absorption probability in the fuel. As a result, the infinite multiplication factor is increased while the fuel temperature coefficient is decreased.