To develop metallic fuel with ultra-high burnup of 30%-40%, an annular U-10Zr fuel with 55% smear density was fabricated through a casting route and irradiated at the Advanced Test Reactor at Idaho National Laboratory. The annular fuel design also serves as a demonstration of the feasibility to replace the sodium bond with a helium bond to benefit the geological disposal of irradiated fuel, cut the cost of fuel fabrication, and boost the overall metallic fuel economy. This paper reports the results from transmission electron microscopy (TEM) based post-irradiation examination of this fuel type irradiated to a burnup of 3.3% fissions per initial heavy metal atoms. The low burnup was planned for initial screening of this fuel design. After irradiation, the initial U-10Zr microstructure separated into an α-U annular region and an UZr_2+x center region with a nanoscale spinodal decomposed microstructure. Because of the large amount of interface areas created in this microstructure, the fission gas atoms and vacancies generated in the UZr_2+x phase are possibly pinned at the interface areas, leading to ∼20 times smaller fission gas bubbles than those in the neighboring α-U. The large bubbles in α-U become connected and merged into large pores that provide fast paths for fission gas release into capsule plenum which prevents further swelling of fuel slug. The fuel slug center still has open space to accommodate further fuel swelling from solid fission products at higher burnup. Other neutron irradiation induced phase and microstructure change are also characterized and compared with traditional solid fuel designs.

为了开发具有30％-40％的超高燃耗的金属燃料，通过铸造路线制造了环状污点密度为55％的U-10Zr燃料，并在爱达荷州国家实验室的先进测试反应堆上进行了辐照。环形燃料设计还证明了用氦键替代钠键的可行性，从而有利于对被辐照燃料进行地质处置，降低了燃料制造成本，并提高了总体金属燃料经济性。本文报道了基于透射电子显微镜（TEM）的这种燃料类型的辐照后检查结果，该燃料类型被辐照为每个初始重金属原子燃耗为3.3％裂变。低燃耗计划用于此燃料设计的初步筛选。辐照后，初始的U-10Zr微观结构分为一个α-U环形区域和一个UZr_{2 + x}中心区域具有纳米级旋节线分解的微观结构。由于在该微结构中形成了大量的界面区域，因此在UZr _{2 + x}相中产生的裂变气体原子和空位可能被钉扎在界面区域，从而导致的裂变气泡比周围α中的裂变气泡小约20倍。 -U。α-U中的大气泡相互连接并汇聚成大孔，为裂变气体释放到胶囊室提供了快速路径，从而阻止了燃料块的进一步膨胀。燃料块芯中心仍然具有开放空间，以适应在更高燃耗下来自固体裂变产物的进一步燃料膨胀。还对其他中子辐照引起的相和微结构变化进行了表征，并与传统的固体燃料设计进行了比较。