Preparation and Characterization of Large Grain UO2 for Accident Tolerant Fuel

Yi Zhong,Zhiyi Wang,Liang Cheng,Biaojie Yan,Yun Wang,Qiqi Huang,Limei Duan,Bin Bai,Rui Gao,Mingfu Chu,Tong Liu,Pengcheng Zhang,Xuxu Liu,Rui Li,Zhenliang Yang,Bingqing Li

doi:10.3389/fmats.2021.651074

Abstract

Large grain UO2 is considered as an accident tolerant fuel with great application potential due to its competitive advantage of good fission gas retention. In this paper, the influence of preparation parameters such as sintering atmosphere, mixing process, powder pretreatment and grain growth additives on the grain size of UO2 is systematically studied. The result shows that the factors mentioned above have different effects on the grain size of UO2. The grain growth of UO2 pellet sintered in oxidizing atmosphere is better than those in reducing atmosphere. The wet mixing process has a significant advantage over the dry mixing process. In addition, the powder pretreatment has little effect on grain growth while the influence of additives plays the main role. Large grain UO2 pellets with uniform grain size up to 150 μm are successfully prepared. Finally, the thermo-physical properties of the pellets are investigated.

Highlights

After the Fukushima accident in 2011, the Accident Tolerant Fuels (ATFs) has been paid much attention by researchers
According to the defect chemistry theory by Cooper, additives can increase the concentration of negatively charged uranium vacancies and promote UO2 grain growth (Cooper et al, 2018)
The results showed that the influence of additives on the grain growth of UO2 is the most obvious

Summary

INTRODUCTION

After the Fukushima accident in 2011, the Accident Tolerant Fuels (ATFs) has been paid much attention by researchers. As a kind of ATF fuels, large grain UO2 fuel is characterized as the significantly increased UO2 grain size in the fuel pellet, by adding trace additives and optimized preparation process. The effects of different additives, mixing methods, powder pretreatment processes, forming pressure, and sintering atmosphere on the grain growth of UO2 were systematically studied. Spark Plasma Sintering (SPS) can activate the powder and realize the densification of high melting point materials in a short time In this experiment, the difference between SPS pre-sintering granulation and traditional cold press granulation was investigated. The SPS pre-sintering granulation process was heating the powder at 800°C for 1 min. The sintered pellet was processed into the final size of Φ8 × 3 mm for the thermal diffusivity test. The sintered pellet was processed into the final size of Φ8 × 13 mm for the thermal expansion test. The specific heat capacity of UO2 can be derived from the following equation (Fink, 2000):

H2-CO2

RESULTS AND DISCUSSIONS

CONCLUSION

DATA AVAILABILITY STATEMENT