NSUF 18-1596: Micro-structural investigation of the pore structure of uncrept and crept irradiated PCEA graphite specimens with SEM and FIB tomography

Graphite has been proposed as a moderator material for the Very High Temperature Reactor (VHTR) reactors designs. The lifetime of VHTR depends on the extent of changes produced by irradiation on the dimensions and graphite properties. As part of the US graphite creep irradiation program known as Advanced Graphite Creep-1 (AGC-1) several grades of graphite have been irradiated at the range of the operation conditions of a VHTR. PCEA graphite specimens of the AGC-1 program will be used to understand the pore evolution under different irradiation and creep conditions. Few studies are available of the irradiation and creep effects on the 3D microstructure of graphite, due to the limitations of standard microscopy techniques. In this study, the authors will adapt a well stablished characterization technique called Focused Ion Beam (FIB) FIB tomography to study the pore characteristics of the binder and filler phase in irradiated and crept graphite specimens. FIB tomography consists in alternating SEM imaging and FIB erosion to obtain sequential images and generate 3D models. This technique can be performed at ORNL’s LAMDA laboratory using the FEI Versa instrument and the Slice & View software. These 3D models can be manipulated to obtain the volume fraction porosity, connectivity of the pore network, shape, and pore-size distribution of the samples.

Three sets of PCEA graphite specimens will be used: an unirradiated sample, 2 crept irradiated sample and 2 uncrept irradiated samples. The crept irradiated samples have a nominal irradiation temperature of 700°C and total neutron fluences of 4.4 and 5.7 dpa. Similarly, the uncrept irradiated samples have a nominal irradiation temperature of 700°C and total neutron fluences of 3.9 and 5 dpa. These conditions will allow the investigation of the pore structure at three different stages of dimensional changes, namely the original volume, initial volume shrinkage, and deep volume shrinkage. This research will also provide fundamental understanding of the changes produced by irradiation and irradiation creep on different types of graphite porosity (unfilled voids, gas entrapment pores, and thermal cracks) that cannot be normally distinguished with conventional 3D imagining techniques such as X-ray tomography.

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필드	값
Abstract	Graphite has been proposed as a moderator material for the Very High Temperature Reactor (VHTR) reactors designs. The lifetime of VHTR depends on the extent of changes produced by irradiation on the dimensions and graphite properties. As part of the US graphite creep irradiation program known as Advanced Graphite Creep-1 (AGC-1) several grades of graphite have been irradiated at the range of the operation conditions of a VHTR. PCEA graphite specimens of the AGC-1 program will be used to understand the pore evolution under different irradiation and creep conditions. Few studies are available of the irradiation and creep effects on the 3D microstructure of graphite, due to the limitations of standard microscopy techniques. In this study, the authors will adapt a well stablished characterization technique called Focused Ion Beam (FIB) FIB tomography to study the pore characteristics of the binder and filler phase in irradiated and crept graphite specimens. FIB tomography consists in alternating SEM imaging and FIB erosion to obtain sequential images and generate 3D models. This technique can be performed at ORNL’s LAMDA laboratory using the FEI Versa instrument and the Slice & View software. These 3D models can be manipulated to obtain the volume fraction porosity, connectivity of the pore network, shape, and pore-size distribution of the samples. Three sets of PCEA graphite specimens will be used: an unirradiated sample, 2 crept irradiated sample and 2 uncrept irradiated samples. The crept irradiated samples have a nominal irradiation temperature of 700°C and total neutron fluences of 4.4 and 5.7 dpa. Similarly, the uncrept irradiated samples have a nominal irradiation temperature of 700°C and total neutron fluences of 3.9 and 5 dpa. These conditions will allow the investigation of the pore structure at three different stages of dimensional changes, namely the original volume, initial volume shrinkage, and deep volume shrinkage. This research will also provide fundamental understanding of the changes produced by irradiation and irradiation creep on different types of graphite porosity (unfilled voids, gas entrapment pores, and thermal cracks) that cannot be normally distinguished with conventional 3D imagining techniques such as X-ray tomography.
Award Announced Date	2018-09-17T12:09:23.383
Awarded Institution	Center for Advanced Energy Studies
Facility	Microscopy and Characterization Suite
Facility Tech Lead	Kory Linton, Yaqiao Wu
Irradiation Facility	None
PI	Cristian Contescu
PI Email	[email protected]
Project Type	RTE
RTE Number	1596