Abstract

The development and qualification of nuclear thermal propulsion (NTP) fuel element technologies would be aided by an in-depth model of material response and failure modes at operating conditions. Integrated computational materials engineering techniques have the potential to provide such a model, as demonstrated here through three case studies focused on a tungsten–uranium mononitride (UN) cermet fuel. The first case focuses on the erosion of tungsten (also named wolfram), a nominal coating/cladding and fuel element matrix material, in hot hydrogen. Ab initio techniques are used to calculate erosion rates and thermal expansion at NTP operating conditions. The second focuses on the stability of UN fuels at high temperature and in the presence of hydrogen. Phase diagram techniques augmented with ab initio thermodynamic data reveal potential instabilities and decomposition pathways at high hydrogen concentrations. The third focuses on using microstructure information to predict high-temperature mechanical response and failure of tungsten. Combined finite element and discrete dislocation dynamics techniques provide mechanical properties in agreement with experimental methods. The integration of these techniques for an all-encompassing material model is discussed.

摘要

核热推进 (NTP) 燃料元件技术的开发和鉴定将得到运行条件下材料响应和失效模式的深入模型的帮助。综合计算材料工程技术有可能提供这样的模型，正如这里通过三个专注于一氮化钨 (UN) 金属陶瓷燃料的案例研究所证明的那样。第一个案例侧重于钨（也称为钨），一种标称涂层/包层和燃料元件基质材料，在热氢气中的侵蚀。Ab initio 技术用于计算 NTP 操作条件下的侵蚀率和热膨胀。第二个重点是联合国燃料在高温和氢气存在下的稳定性。从头算热力学数据增强的相图技术揭示了高氢浓度下的潜在不稳定性和分解途径。第三个重点是使用微观结构信息来预测钨的高温机械响应和失效。结合有限元和离散位错动力学技术提供与实验方法一致的机械性能。讨论了将这些技术集成到一个包罗万象的材料模型中。