NSUF 18-1282: In-situ High Temperature Ion Irradiation Transmission Electron Microscopy to Understand Fission Product Transport in Silicon Carbide of TRISO Fuel

The overall goal of this project is to demonstrate the use of in-situ electron microscopy under high temperature ion irradiation for characterization of advanced nuclear fuel. This project will capture the real time events of fission products transport in neutron irradiated Tristructural Isotropic (TRISO) fuel. In spite of advanced microscopy methods and modeling effort, the fission product transport mechanisms in silicon carbide (SiC), a coating layer in TRISO fuel, under high temperature and neutron fluence remains controversial. It has been found that the transport mechanism of individual fission product in SiC can be different based on their mobility and melting temperature, and can potentially affect its high temperature stability. Fission products, and various compounds of fission products were identified as single and-or multi-phases predominantly at the grain boundaries. From these results, it is not clear if the phases occurred during segregation during the cooling, or if the compounds are transporting as the compounds. Additionally, recent research effort has demonstrated that the intragranular fission product precipitation is accomplished via an interesting two-step nucleation route. In the first step, nanoscale alpha-SiC precipitates in a beta-SiC matrix unexpectedly nucleate heterogeneously at structural defects. This occurs at significantly lower temperatures compared with the usual beta-alpha transition temperature. Subsequently, alpha-SiC precipitate acts as a surrogate template for its structural and compositional transition into a fission product precipitate. In the traditional room temperature characterization of silicon carbide SiC via transmission electron microscopy (TEM), it is difficult to resolve the complexity of simultaneous and interdependent high temperature diffusion processes that leads to this structural defect assisted intergranular fission product transport as well as the intergranular precipitation. The success of TRISO fuel further requires innovative characterization approaches such as in-situ TEM under high temperature and simultaneous ion implantations that can provide real time data of complex diffusion processes. The ability to observe dynamic radiation induced structural and compositional changes at sub-nanometer scale by in-situ TEM experiments is definitely a complementary yet vital addition to the present Advanced Gas Reactor (AGR) post irradiation microstructural characterization.

Additional Info

Field	Value
Abstract	The overall goal of this project is to demonstrate the use of in-situ electron microscopy under high temperature ion irradiation for characterization of advanced nuclear fuel. This project will capture the real time events of fission products transport in neutron irradiated Tristructural Isotropic (TRISO) fuel. In spite of advanced microscopy methods and modeling effort, the fission product transport mechanisms in silicon carbide (SiC), a coating layer in TRISO fuel, under high temperature and neutron fluence remains controversial. It has been found that the transport mechanism of individual fission product in SiC can be different based on their mobility and melting temperature, and can potentially affect its high temperature stability. Fission products, and various compounds of fission products were identified as single and-or multi-phases predominantly at the grain boundaries. From these results, it is not clear if the phases occurred during segregation during the cooling, or if the compounds are transporting as the compounds. Additionally, recent research effort has demonstrated that the intragranular fission product precipitation is accomplished via an interesting two-step nucleation route. In the first step, nanoscale alpha-SiC precipitates in a beta-SiC matrix unexpectedly nucleate heterogeneously at structural defects. This occurs at significantly lower temperatures compared with the usual beta-alpha transition temperature. Subsequently, alpha-SiC precipitate acts as a surrogate template for its structural and compositional transition into a fission product precipitate. In the traditional room temperature characterization of silicon carbide SiC via transmission electron microscopy (TEM), it is difficult to resolve the complexity of simultaneous and interdependent high temperature diffusion processes that leads to this structural defect assisted intergranular fission product transport as well as the intergranular precipitation. The success of TRISO fuel further requires innovative characterization approaches such as in-situ TEM under high temperature and simultaneous ion implantations that can provide real time data of complex diffusion processes. The ability to observe dynamic radiation induced structural and compositional changes at sub-nanometer scale by in-situ TEM experiments is definitely a complementary yet vital addition to the present Advanced Gas Reactor (AGR) post irradiation microstructural characterization.
Award Announced Date	2018-02-01T14:20:06.017
Awarded Institution	None
Facility	None
Facility Tech Lead	Michael Starr
Irradiation Facility	None
PI	Isabella van Rooyen
PI Email	[email protected]
Project Type	RTE
RTE Number	1282