颗粒团聚行为对弥散型核燃料芯体失效的影响分析

Analysis of Particle Agglomeration Effect on Failure of Dispersion Nuclear Fuel Meat

针对燃料颗粒团聚行为对弥散型核燃料芯体失效的影响,开发了弥散型核燃料元件代表性体元模型的参数化建模及数值计算脚本,综合考虑燃料-基体界面损伤层、燃料颗粒辐照肿胀以及环境压力等关键特征进行了数值建模,系统分析了燃料颗粒团聚体积分数、颗粒团聚位置、运行环境静水压力以及基体材料性质对弥散型核燃料芯体失效的影响规律,发现燃料颗粒团聚区域是弥散型核燃料芯体失效的起点,而运行环境静水压力对芯体应力集中有抑制作用,揭示了燃料颗粒团聚现象对弥散型核燃料元件力学性能的“短板效应”。团聚区域的燃料颗粒通过密集堆叠的方法进行几何建模,局部燃料颗粒团聚体积分数由最小颗粒间距定义。有限元计算结果表明,燃料颗粒团聚体积分数越大,弥散型核燃料芯体越容易失效。而包壳外的环境压力会降低芯体内燃料颗粒团聚区域的应力水平,但随着局部团聚程度的增加,环境压力对芯体中Mises应力的影响逐渐减小。此外,燃料颗粒团聚区域相对弥散型核燃料芯体厚度方向位置改变对芯体的最大Mises应力几乎没有影响;燃料颗粒团聚区域在弥散型核燃料芯体的面内分布位置和环境压力共同决定弥散型核燃料芯体的失效行为。本研究可为弥散型核燃料元件的失效条件预测、可靠性评估和结构优化设计提供分析方法和数值依据。

By dispersing the fuel particles in an inert metal matrix,the dispersion nuclear fuel element has the advantages of high burnup,high thermal conductivity,great safety and strong designability,etc.It has been successfully applied in the test reactors.Within a dispersion nuclear fuel element,the failure of fuel meat is significantly influenced by the particle agglomeration behavior,including the agglomeration extent,the location of agglomeration region,fuel particle spacing,etc.The present study investigates the crucial factors influencing the failure behavior in the dispersion nuclear fuel meat,focusing on the particle agglomeration effect on the failure of fuel meat.By developing a script for parametric modeling and numerical calculations of the representative volume element in the dispersion nuclear fuel element,the Mises stress field of dispersion nuclear fuel meat incorporating with different particle agglomeration characteristics was simulated in this paper.Numerical modeling was performed by considering the damage layer at the fuel-matrix interface,irradiation-induced fuel particles swelling and the environmental pressure outside the cladding.The effects of particle agglomeration volume fraction,location of the agglomerate fuel particles,ambient hydro-static pressure and matrix material properties on the failure of dispersion nuclear fuel meat were analyzed systematically.The fuel particles in agglomeration region were geometrically modeled through dense stacking,while the local particle agglomeration volume fraction was defined by the minimum particle spacing.The results show that the failure behavior in dispersion nuclear fuel meat is enhanced with the increasing of particle agglomeration volume fraction.The environmental pressure outside the cladding can inhibit the stress concentration in the dispersion fuel meat,but this influence declines with the extent of local fuel agglomeration increasing.Furthermore,the particle agglomeration location between the upper and lower cladding layers of the thin plate indicates little effect on the maximum Mises stress in the dispersion nuclear fuel meat.However,compared to the dispersion meat adjacent to the surrounding cladding,fuel particles agglomerating in central meat(i.e.only constrained by the upper and lower cladding)are more sensitive to environmental pressure.The local fuel particle agglomeration has a shortest stave effect on the failure of dispersion nuclear fuel meat.The volume fraction of agglomeration will seriously exacerbate the stress concentration,and the agglomeration location in the interior of dispersion fuel meat will fail first.Therefore,it is concluded that the extent of fuel particle agglomeration,the location of agglomeration region within the dispersion nuclear fuel meat,and the environmental pressure are crucial factors influencing the failure behavior of fuel meat.The fuel particle agglomeration region is the onset location for the local macroscopic failure,and the environmental pressure outside the cladding can decrease the plastic stress concentration in the dispersion fuel meat to improve the safety of reactor core.This work provides an analytical approach and numerical reference for the failure condition prediction,the reliability evaluation,and the structural optimization design of the plate dispersion nuclear fuel element.