The influence of a reactor overpower transient on irradiated metallic fuel performance was investigated in this work. Such transient studies support safety and performance optimization of future sodium fast reactors. A ternary metallic fuel alloy (U-19Pu-10Zr) in HT-9 cladding which was irradiated in the Experimental Breeder Reactor II (EBR-II) to a burnup of 11 at. %, and then subjected to a 30% overpower transient was studied. The sample was selected from the top of a fuel pin where failure is expected to first appear in the EBR-II pin design. This can occur when the pin is subjected to conditions beyond its design envelope. Main elemental distribution, phase characterization, fission product behavior, chemical form and fuel-cladding chemical interaction were analyzed in this study. Simulation of the temperature profile during the transients were performed using BISON and show that the moderate transient did not maintain prolonged high temperature. For the first time, the porous structure commonly found at the top of metallic fuel pin (termed “fluff” structure given its appearance) was examined in detail via postirradiation characterization. The fluff contains the major fuel elements (U, Pu, Zr) and presents a highly porous microstructure (over 40% area fraction). The presence of fission products relevant to source term was investigated. However, semi-volatile and volatile elements (namely Cs, I, Xe, Eu), expected in this region, could not be detected probably due to sample preparation. Europium, also expected in this region, was only detected in precipitates along with the other rare earth elements. Finally, no fluff (fuel) fragments detached from the fuel slug were detected in the plenum region, indicating the fluff stability under the tested moderate ramp. These analyses indicate that the moderate transient experienced by the fuel pin did not significantly influence fuel performance under this transient condition.

在这项工作中，研究了反应堆过功率瞬变对辐射金属燃料性能的影响。这种瞬态研究为未来的钠快堆的安全性和性能优化提供了支持。在HT-9包覆层中的三元金属燃料合金（U-19Pu-10Zr）在实验增殖反应堆II（EBR-II）中辐照到11 at。的燃尽。％，然后进行30％的过功率瞬变研究。从燃料销的顶部选择样品，预计在EBR-II销的设计中首先会出现故障。当引脚处于超出其设计范围的条件下时，可能会发生这种情况。本研究分析了主要元素分布，相特征，裂变产物行为，化学形式和燃料-包壳化学相互作用。使用BISON对瞬态过程中的温度曲线进行了仿真，结果表明中等的瞬态过程无法维持长时间的高温。首次通过辐照后表征详细检查了金属燃料销顶部常见的多孔结构（在外观上称为“绒毛”结构）。绒毛包含主要的燃料元素（U，Pu，Zr），并呈现出高度多孔的微观结构（面积分数超过40％）。研究了与源术语有关的裂变产物的存在。但是，可能由于样品制备而无法检测到该区域中预期的半挥发性和挥发性元素（即Cs，I，Xe，Eu）。在该区域也预期有,，仅在沉淀物中与其他稀土元素一起被检测到。最后，在气室区域中未检测到从燃料块中脱落的绒毛（燃料）碎片，表明在测试的中等坡度下的绒毛稳定性。这些分析表明，在这种瞬态条件下，燃料销经历的适度瞬变不会显着影响燃料性能。