集成学习方法在碳化硅陶瓷微封装燃料芯块烧结工艺优化中的应用研究

Application of Ensemble Machine Learning Method to Sintering Process Optimization of SiC-ceramic Microencapsulated Fuel Pellets

  • 摘要: 2011年日本福岛核事故后,为弥补UO2-Zr燃料固有的缺陷,研制一种提高反应堆堆芯抵御严重事故能力的新型燃料,耐事故燃料(accident tolerant fuel, ATF)的开发和研究受到越来越多的关注,碳化硅陶瓷微封装燃料芯块在ATF领域显示出独特的优势。然而,由于工艺摸索实验成本高、时间长,新型核燃料的开发受到了阻碍。数据驱动方法可极大提高新材料开发的效率。本文构建了集成学习框架,收集实验数据,构建工艺参数与碳化硅陶瓷微封装燃料芯块的烧结性能之间的映射模型,预测不同工艺参数条件下的烧结性能,阐明影响烧结性能的重要因素。此外,采用粒子群优化(particle swarm optimization, PSO)算法对工艺参数空间进行搜索,推荐具有最优烧结性能应具备的工艺条件。结果表明,集成学习模型在测试集上的预测值与实验值之间的拟合优度R2>0.99,均方根误差RMSE<0.01,平均绝对误差MAE<0.01,且分析得到的影响烧结性能的参数重要性与物理知识一致,表明了本方法的准确性及可解释性。本文方法为加速开发新的核燃料提供了理论指导。

     

    Abstract: After the Fukushima nuclear accident in Japan in 2011, in order to make up for the inherent defects of UO2-Zr fuel, a new fuel has been developed to improve the capability of reactor core to withstand serious accidents. The development and research of accident tolerant fuel (ATF) has received more and more attention. SiC ceramic microencapsulated fuel pellets show unique advantages in the field of ATF, and is widely studied as a fuel core due to its high thermal conductivity, low density variation with temperature, and good specific heat properties. However, the development of new nuclear fuels has been hampered by the high cost and time-consuming of nuclear fuel experiments. Recently, data-driven approaches can greatly improve the efficiency of new material design and development, such as material property prediction, processing parameter optimization, descriptor extraction and materials design. In this paper, an interpretable machine learning framework was developed to predict sintering performance and optimize process parameters. First, sintering process parameters and sintering performance data were collected from the experiments. Then, based on dataset, a machine learning model between process parameters and the sintering performance of SiC-ceramic microencapsulated fuel particles was constructed. After that, well-trained model was used to predict the sintering performance under different process parameter conditions. Specifically, in order to make machine learning models interpretable and trustfull, feature importance analysis was developed to compute the importance of each process parameter, elucidating the important factors affecting the sintering performance. The results show that the goodness of fit between the predicted and experimental values of the machine learning model on the test set is R2>0.99, RMSE and MAE are about 0.01, and the parameters affecting the sintering performance obtained from the analysis are consistent with the physical knowledge, indicating the accuracy and interpretability of the proposed framework. In addition, a particle swarm optimization (PSO) algorithm was used to search the process parameter space and obtain the process parameters that should have the optimal sintering performance. Lastly, in order to verify the effectiveness of inverse design, pellet density and metallographic diagram under the recommended optimum process parameters were obtained through experimental characterization. The experimental results show that the recommended process parameters with PSO are consistent with experimental results and achieving good sintering performance, demonstrating the feasibility and accuracy of the propsed framework. This work provides theoretical guidance for accelerating the development of new nuclear fuel and also paves a way for the design and development of other materials.

     

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