High temperature in-situ synchrotron-based XRD study on the crystal structure evolution of C/C composite impregnated by FLiNaK molten salt

Shanglei Feng,Xingtai Zhou,Long Yan,Yingguo Yang,Dongsheng Zhang,Xinmei Yang,Derek K L Tsang,Huihao Xia,Li Li,Ping Huai

doi:10.1038/s41598-017-11033-2

Abstract

An in-situ real-time synchrotron-based grazing incidence X-ray diffraction was systematically used to investigate the crystal structural evolution of carbon fiber reinforced carbon matrix (C/C) composite impregnated with FLiNaK molten salt during the heat-treatment process. It was found that the crystallographic thermal expansion and contraction rate of interlayer spacing d002 in C/C composite with FLiNaK salt impregnation is smaller than that in the virgin sample, indicating the suppression on interlayer spacing from FLiNaK salt impregnated. Meanwhile the crystallite size LC002 of C/C composite with FLiNaK salt impregnation is larger than the virgin one after whole heat treatment process, indicating that FLiNaK salt impregnation could facilitate the crystallization of C/C composite after heat treatment process. This improved crystallization in C/C composite with FLiNaK salt impregnation suggests the synthetic action of the salt squeeze effect on crooked carbon layer and the release of internal residual stress after heating-cooling process. Thus, the present study not only contribute to reveal the interaction mechanism between C/C composite and FLiNaK salt in high temperature environment, but also promote the design of safer and more reliable C/C composite materials for the next generation molten salt reactor.

Highlights

Molten salt reactor (MSR) has been regarded as one of the most promising candidates for Generation IV Nuclear Energy System because of its unique fuel cycle capabilities and safety characteristics[1,2,3]
The evolutions of graphite interlayer spacing d002 and corresponding crystallite size LC002 during the heat-treatment process of carbon fiber reinforced carbon matrix (C/C) composite samples with and without FLiNaK salt impregnation were obtained by 1D-grazing incidence X-ray diffraction (GIXRD). 2D-GIXRD was further investigated the crystallographic orientation of C/C composite to perform the change of crystal texture
The LC002 of C/C composite with FLiNaK salt impregnation is larger than the virgin one after cooled down to 30 °C (RT), indicating that FLiNaK salt impregnation could facilitate the crystallization of C/C composite after whole heat treatment process

Summary

Introduction

Molten salt reactor (MSR) has been regarded as one of the most promising candidates for Generation IV Nuclear Energy System because of its unique fuel cycle capabilities and safety characteristics[1,2,3]. It is highly desirable to in-situ study the crystal structure evolution of the C/C composite impregnated by high temperature liquid molten salt to reveal the interaction mechanism between C/C composite and FLiNaK (46.5%LiF-11.5%NaF-42%KF (mol%)) salt, since the C/C composite control rod guider in a MSR is exposed directly in the high temperature liquid molten salt. 2D-GIXRD was further investigated the crystallographic orientation of C/C composite to perform the change of crystal texture All these achievements will contribute to deeply understand the interaction mechanism between C/C composite and FLiNaK salt in high temperature environment and promote to design the safer and more reliable molten salt reactor of generation

Methods

Results

Conclusion