球形燃料元件温度分布对包覆燃料颗粒失效概率的影响

固态熔盐堆采用TRISO(Tristructural isotropic)包覆颗粒球形燃料元件。在运行工况下,燃料元件内部存在一定的温度分布,填充在燃料元件内部不同位置的TRISO颗粒的失效概率会因此受到影响。利用体积微元的方法分析了温度分布对包覆颗粒失效概率的影响,并进一步研究了球形燃料元件尺寸对TRISO颗粒平均失效概率的影响。结果表明,在一定的功率密度下,如果利用球心温度或者平均温度计算燃料元件内部TRISO颗粒的平均失效概率,结果相比实际值会有至少一个数量级的差别;在相同功率密度和相同燃耗条件下,燃料元件直径每减小1 cm,其包覆颗粒平均失效概率降低两个数量级左右。

Effects of temperature distribution on failure probability of coated particles in spherical fuel elements

Background:Particles coated by TRISO (Tristructural isotropic) embedded in spherical fuel elements are used in solid fuel molten salt reactor. Temperature distribution during operation can affect the failure probability of TRISO particles embedded in different parts of fuel elements. Purpose: This study aims to investigate the temperature distribution effects on failure probability of coated fuel particles. Methods: Micro-volume element analysis of temperature distribution effect on the failure probability of coated particles was carried out for the first time, and the impact of spherical fuel element size on the average failure probability of TRISO particles was also evaluated. Results: At a given power density, the failure probability of TRISO particles would be deviated by an order of magnitude when either core temperature or average temperature of the fuel element was used to calculate the average failure probability. With the same power density and the same burnups, the average failure probability of coated particles could be lowered by two orders of magnitude through reducing the diameter of fuel element by 1 cm. Conclusion:It is necessary to take the temperature distribution into account for calculating the failure probability of coated fuel particles. In addition, it is found that the average failure probability of coated fuel particles can be lowered by reducing the sizes of the fuel element. This may be a proper way to secure the fuel elements working at high power densities.