Uranium mononitride (UN) has long been considered a potential high density, high performance fuel candidate for light water reactor (LWR) and fast reactor (FR) applications. However, deployability of this fuel has been limited by the notable resistance to sintering and subsequent difficulty in producing a desirable microstructure, the high costs associated with ¹⁵N enrichment, as well as the known proclivity to oxidation and interaction with steam. In this study, the stimulation of grain growth in UN pellets sintered using SPS has been investigated. The results reveal that by using SPS and controlling temperature, time, and holding pressure, grain growth can be stimulated and controlled to produce a material featuring both a desired porosity and grain size, at least within the range of interest for nuclear fuel candidates. Grain sizes up to 31 μm were obtained using temperatures of 1650 °C and hold times of 15 min. Evaluation by EBSD reveal grain rotation and coalescence as the dominant mechanism in grain growth, which is suppressed by the application of higher external pressure. Moreover, complete closure of the porosity of the material was observed at relative densities of 96% TD, resulting in a material with sufficient porosity to accommodate LWR burnup. These results indicate that a method exists for the economic fabrication of an ¹⁵N-bearing uranium mononitride fuel with favorable microstructural characteristics compatible with use in a light water-cooled nuclear reactor.

长期以来，单氮化铀（UN）被认为是轻水反应堆（LWR）和快堆（FR）应用的潜在高密度，高性能燃料候选者。但是，这种燃料的可部署性受到显着的抗烧结性和随后难以产生所需微结构的限制，这与^15的高成本有关。氮富集，以及氧化和与蒸汽相互作用的已知倾向。在这项研究中，已经研究了使用SPS烧结UN颗粒对晶粒长大的刺激作用。结果表明，通过使用SPS并控制温度，时间和保持压力，可以刺激和控制晶粒的生长，以生产出兼具所需孔隙率和晶粒尺寸的材料，至少在候选核燃料感兴趣的范围内。使用1650°C的温度和15分钟的保持时间可获得最大31μm的晶粒尺寸。EBSD的评估表明，晶粒旋转和聚结是晶粒生长的主要机制，而较高的外部压力则抑制了晶粒的旋转和聚结。此外，在相对密度为96％TD时观察到材料的孔隙率完全封闭，导致材料具有足够的孔隙度以适应LWR燃耗。这些结果表明，存在一种经济地制造部件的方法。具有良好的微结构特征的^15种含氮单氮化铀燃料，可与轻型水冷核反应堆兼容。