弥散型燃料的裂变气体行为研究

Study on the Fission Gas Behaviors of Dispersion Fuel

探讨了弥散型燃料中对辐照肿胀有重要影响的裂变气体的行为机理。裂变气体原子聚集成气泡引起燃料相肿胀，气泡的尺寸分布是影响辐照肿胀的重要因素。决定气泡生长的裂变气体的行为机理主要有：裂变气体原子的产生和热扩散迁移，气泡的成核和聚合长大，气泡内气体原子的重溶，燃料相的辐照亚晶化等过程。燃料中各种尺寸的气泡浓度随时间的变化率可用气泡生长的动力学速率方程组来描述。当裂变密度较高时，辐照产生的缺陷引起燃料相的亚晶化。亚晶界网络的出现加速了气泡聚合过程，引起大尺寸气泡的产生，辐照肿胀随裂变密度加速增加。在一定辐照条件下拐点燃耗随温度增加而减小，温度是影响弥散型燃料辐照肿胀非常重要的因素。本文计算了一定条件下 U3Si2- Al弥散型燃料的辐照肿胀随裂变密度的变化。对照表明，理论计算值与实验测量值相一致，有关裂变气体的行为机理模型能有效地预测一定运行条件下弥散型燃料的辐照肿胀规律。

This paper discussed the behavior mechanism of fission gas which dominate the irradiation swelling processes of dispersion fuel.Fission gas atoms coalesce into gas bubbles,which induce fuel swelling.The size distribution of gas bubbles plays an important role in the irradiation swelling.The critical fission gas actions which contribute to the growth of gas bubbles are as following:The production of fission gas atoms,gas migration through thermal diffusion,fission gas bubble nucleation,bubble coalescence and growth,gas atom re- solution and irradiation induced grain subdivision of fuel.To analyze the growth of gas bubbles,the dynamic rate equations are used to describe the time dependent concentration of gas bubbles of various sizes in the fuel.At high fission density,the irradiation induced defects lead to the subdivision of the fuel crystalline grains.The subgrain boundary net work promotes the growth of large gas bubbles.This accelerates the rate of irradiation swelling versus fission density.Under specific irradiation conditions,the knee burnup decreases as the irradiation temperature increases.Therefore,the temperature is a key factor in the irradiation swelling of dispersion fuel.In this paper,the irradiation swelling of U3Si2- Al dispersion fuel versus fission density was calculated under specific irradiation conditions.The theoretically calculated values are confirmed with the experimental data in comparison.The mechanistic model of the fission gas behavior can be used to analyze,elucidate and predict the irradiation swelling of dispersion fuel effectively.