Accelerating the nuclear fuel qualification process will rely on some combination of advanced modeling and simulation techniques with accelerated irradiation testing and separate effects experiments to enable the development of new fuel concepts in a shorter time frame. One of the key challenges to successfully leveraging accelerated irradiation tests will be understanding the artifacts that may be introduced with accelerated accumulation of dose and/or burnup. This work presents phase field (MARMOT) simulations of the evolution of representative 2D UO microstructures up to 40 MWd/kgU. Simulations were performed under both commercial light water reactor fuel conditions as well as those that would be expected for highly accelerated (∼10x) burnup conditions similar to those used in the MiniFuel irradiations in Oak Ridge National Laboratory's High Flux Isotope Reactor. The phase field model was coupled with a discrete nucleation algorithm to model restructuring at high burnup. The effect of the different fission rates in both microstructures was investigated at two temperatures: 650C and 800C. The lower temperature simulations both showed an onset of restructuring at nearly 60 MWd/kgU. More extensive restructuring was obtained in the MiniFuel microstructure compared with that of the PWR fuel. At 800C, no restructuring was obtained as a result of the thermally activated diffusion of Xe atoms and U vacancies to fission gas bubbles, which reduces the nucleation driving force. These results highlight the importance of using modeling and simulation tools to inform the environmental conditions during targeted accelerated irradiation tests to extract the most useful fuel performance data.

中文翻译：

---

加速燃耗对 UO2 微观结构演化影响的中尺度建模

加速核燃料鉴定过程将依赖于先进建模和模拟技术与加速辐照测试和单独效应实验的某种结合，以便能够在更短的时间内开发新燃料概念。成功利用加速辐照测试的关键挑战之一是了解随着剂量和/或燃耗的加速累积可能引入的伪影。这项工作提出了高达 40 MWd/kgU 的代表性 2D UO 微观结构演化的相场 (MARMOT) 模拟。模拟是在商用轻水反应堆燃料条件以及预期的高度加速（~10x）燃耗条件下进行的，类似于橡树岭国家实验室高通量同位素反应堆中小型燃料辐照中使用的条件。相场模型与离散成核算法相结合，对高燃耗下的重组进行建模。在两个温度：650°C 和 800°C 下研究了两种微观结构中不同裂变速率的影响。较低温度模拟均显示重组开始于接近 60 MWd/kgU。与压水堆燃料相比，MiniFuel 微观结构获得了更广泛的重组。在800℃时，由于Xe原子和U空位热激活扩散到裂变气泡中，没有获得重组，从而降低了成核驱动力。这些结果凸显了在有针对性的加速辐照测试期间使用建模和仿真工具告知环境条件以提取最有用的燃料性能数据的重要性。