An improved prediction model for the effective thermal conductivity of compact pebble bed reactors

作者：You, Ersheng; Sun, Ximing; Chen, Fubing; Shi, Lei^*; Zhang, Zuoyi

来源：Nuclear Engineering and Design, 2017, 323: 95-102.

DOI：10.1016/j.nucengdes.2017.07.041

• Effective thermal conductivity
• ZBS model
• Contact conduction
• Radiation exchange factor
• Pebble bed reactor

The effective thermal conductivity is a lumped parameter, which determines heat transfer processes in pebble bed reactors, especially for the decay heat removal after shutdown. Generally, it is calculated by the ZBS model, where the contact area fraction phi is an empirical value for the description of the contact conduction, and the Argo & Smith formula is used to consider the radiation effect. However, the model underestimates the radiation contribution in high temperature. On the other hand, the influence of packing fractions is not included in the model, which affects both the contact conduction and the radiation effect. Therefore, an improved ZBS model was proposed in the paper with the refinements in these two aspects. The elastic deformation theory and the interpolation of three typical structured packing were introduced in the improved model, to calculate the contact conduction of random packed beds with the consideration of packing fractions. At the same time, the Robold model was employed in the improved model, in replacement of the simple formula used in the old ZBS model, by the comparison of several radiation correlations. It was shown that the Robold model could increase the radiation exchange factor at the temperature more than 1000 degrees C, which is attribute to improve the prediction in high temperature. With the validation by SANA and HTO experiments, it was indicated that the improved model is suitable for the conceptual design and analysis of compact pebble bed reactors with mono-sized spherical fuel elements, where the maximum temperature is possibly close to 1600 degrees C.

• 出版日期2017-11
• 单位清华大学