NSUF 18-1453: Electron Tomography Characterisation of Porosity in IG-110 and NBG-17 Nuclear Graphite Grades

Graphite is the moderator material of some Generation IV reactors concepts and British Advanced Gas-cooled Reactors (AGR). Porosity in nuclear graphite influence most of the material properties and evolution of induced neutron irradiation volumetric changes. Mesopores (<0.1 µm) and micropores (<0.001 µm) play a fundamental role on the shrinkage and swelling of graphite. Through the lifetime of a graphite component neutron irradiation generate mesopores and micropores that change CTE values and permeability of the material. These value changes in CTE promote stress concentrations in both VHTR and MSR graphite components and would promote the infiltration of molten salts into the pores. Due to the small nature of these types of pores only high-resolution techniques like electron tomography are capable of detecting voids smaller than 0.1 µm in a 3D space. This novel characterisation technique of mesopores in graphite would help to understand the link between the changes of material properties in irradiated graphite and mesopores. In addition, the characterisation of mesopores will help to understand the possible mechanisms of molten salt intrusion into mesopores.

Furthermore, electron tomography might provide a better understanding of the “grain” like atomic structure of graphite. Imaging in TEM foils indicate the presence of a grain structure of graphite, however, the thickness, and boundaries are difficult to detect with 2D imaging. The 3D reconstructions could provide a different insight on the grain atomic structure of graphite and therefore its possible behaviour under irradiation. The collected data of this project will contribute to the validation and improvement of the polycrystalline model of irradiation behavior developed in the UK by the National Nuclear Laboratory (NNL). This model requires detailed information of the morphology, grain size and porosity of graphite.

Additional Info

Field	Value
Abstract	Graphite is the moderator material of some Generation IV reactors concepts and British Advanced Gas-cooled Reactors (AGR). Porosity in nuclear graphite influence most of the material properties and evolution of induced neutron irradiation volumetric changes. Mesopores (<0.1 µm) and micropores (<0.001 µm) play a fundamental role on the shrinkage and swelling of graphite. Through the lifetime of a graphite component neutron irradiation generate mesopores and micropores that change CTE values and permeability of the material. These value changes in CTE promote stress concentrations in both VHTR and MSR graphite components and would promote the infiltration of molten salts into the pores. Due to the small nature of these types of pores only high-resolution techniques like electron tomography are capable of detecting voids smaller than 0.1 µm in a 3D space. This novel characterisation technique of mesopores in graphite would help to understand the link between the changes of material properties in irradiated graphite and mesopores. In addition, the characterisation of mesopores will help to understand the possible mechanisms of molten salt intrusion into mesopores. Furthermore, electron tomography might provide a better understanding of the “grain” like atomic structure of graphite. Imaging in TEM foils indicate the presence of a grain structure of graphite, however, the thickness, and boundaries are difficult to detect with 2D imaging. The 3D reconstructions could provide a different insight on the grain atomic structure of graphite and therefore its possible behaviour under irradiation. The collected data of this project will contribute to the validation and improvement of the polycrystalline model of irradiation behavior developed in the UK by the National Nuclear Laboratory (NNL). This model requires detailed information of the morphology, grain size and porosity of graphite.
Award Announced Date	2018-05-17T11:10:37.16
Awarded Institution	None
Facility	None
Facility Tech Lead	Kory Linton
Irradiation Facility	None
PI	Athanasia Tzelepi
PI Email	[email protected]
Project Type	RTE
RTE Number	1453