Evaluation of Oxidation Performance of TRISO Fuel Particles for Postulated Air-Ingress Accident of HTGR

Fangcheng Cao,Hao Li,Hongqing Wang,Qingjie Chen,De Zhang

doi:10.1155/2020/6568987

Abstract

In a high-temperature gas-cooled reactor, the integrity of tristructural-isotropic-(TRISO-) coated fuel particles ensures the safety of the reactor, especially in case of an air-ingress accident. The oxidation of TRISO particles with the outer layers of silicon carbide (SiC) was performed at temperatures of 900°C–1400°C in air environment. Both the microstructure and phase composition of the SiC layers were studied. The results showed that the SiC layers had a good oxidation resistance below 1100°C. However, the amorphous silica on the SiC layers formed at 1200°C and gradually crystallized at 1400°C with the presence of microcracks. The reaction rates of the SiC layers were determined by measuring the silica thickness. It was proposed that the oxidation of the SiC layers followed the linear-parabolic law with the activation energy of 146 ± 5 kJ/mol. The rate-determining step of the oxidation was the diffusion of oxygen in silica.

Highlights

E consequences of air-ingress for TRISO fuel particles have not been adequately addressed to date
As the OPyC layers begin to be oxidized at temperatures higher than 700°C, the exposed silicon carbide (SiC) layers in TRISO particles would play an important role in governing fuel performance. erefore, the investigation of the oxidation performance of the SiC layers is imperative in the safety considerations
Since the microstructure and properties of the SiC layers in TRISO particles are different from those of the SiC plate despite the same coating procedure, the oxidation mechanisms of the SiC layers are needed to be clarified [12]. e impact of annealing in air atmosphere on TRISO particles has been investigated with temperatures up to 1600°C [13,14,15]. e results showed that intense regression of the SiC beneath the rough silica layer occurred at 1600°C, which was affected by the interaction between TRISO particles and the alumina crucible [13]. e mechanisms and kinetics of the oxidation process of the TRISO particles with the outer layers of SiC in air environment under different temperatures still need to be investigated to evaluate the microstructure evolution of the silica layer

Summary

Introduction

E consequences of air-ingress for TRISO fuel particles have not been adequately addressed to date. Since the microstructure and properties of the SiC layers in TRISO particles are different from those of the SiC plate despite the same coating procedure, the oxidation mechanisms of the SiC layers are needed to be clarified [12]. E mechanisms and kinetics of the oxidation process of the TRISO particles with the outer layers of SiC in air environment under different temperatures still need to be investigated to evaluate the microstructure evolution of the silica layer. The oxidation of TRISO particles with the outer layers of SiC was investigated in air environment at the temperature range of 900°C–1400°C. e composition and microstructure of the SiC layers after oxidation was characterized and analyzed. The oxidation of TRISO particles with the outer layers of SiC was investigated in air environment at the temperature range of 900°C–1400°C. e composition and microstructure of the SiC layers after oxidation was characterized and analyzed. e oxidation kinetics of the SiC layer were studied, including oxidation rate, activation energy, and the rate-controlling step, which aims to predict the SiC degradation rate in case of an airingress accident in operation

Methods

Results

Conclusion