NSUF 14-439: APT (LEAP) analyisis of Cs implanted SiC

The project objectives are to determine the pathway of Cs diffusion in the polycrystalline 3C-SiC substrates. The expected results from LEAP will show whether diffusion occurs along grain boundaries or occurs through the polycrystalline bulk material. This result will address a knowledge gap presented by Hobbins et al at the VHTR FY13 meeting. Sample preparation will require the use of a FIB, including an additional Cr protection layer, to produce the sample tips and TEM to verify that the desired region of the sample (recrystallized SiC) is present in the tips prior to analyzing with the LEAP. Samples include two 3 mm diameter x 0.8 mm thick planar TEM disks and two 0.8 mm diameter TRISO SiC hemispheres (produced from ZrO2 surrogate TRISO particles) that have had Cs implanted into the substrate and then recrystallized through a thermal step. The result is a ~250 nm region composed of some ~200 nm grains in a very fine grained SiC matrix. Samples also are subjected to diffusion steps of 10 hours at 1000°C or 1100°C. Understanding how Cs moves through the SiC layer will provide valuable insight into the kinetic mechanism of Cs diffusion in the SiC layer of the Gen IV TRISO fuel particle. If grain boundaries are a significant contributor to the diffusion of Cs it may be necessary to minimize grain boundary area through coarsening. Through discussion with the instrument technicians, the project is estimated to require about 84 hours of instrument time. The samples are presently ready for delivery at the first available opening in instrument booking.

Additional Info

Field	Value
Abstract	The project objectives are to determine the pathway of Cs diffusion in the polycrystalline 3C-SiC substrates. The expected results from LEAP will show whether diffusion occurs along grain boundaries or occurs through the polycrystalline bulk material. This result will address a knowledge gap presented by Hobbins et al at the VHTR FY13 meeting. Sample preparation will require the use of a FIB, including an additional Cr protection layer, to produce the sample tips and TEM to verify that the desired region of the sample (recrystallized SiC) is present in the tips prior to analyzing with the LEAP. Samples include two 3 mm diameter x 0.8 mm thick planar TEM disks and two 0.8 mm diameter TRISO SiC hemispheres (produced from ZrO2 surrogate TRISO particles) that have had Cs implanted into the substrate and then recrystallized through a thermal step. The result is a ~250 nm region composed of some ~200 nm grains in a very fine grained SiC matrix. Samples also are subjected to diffusion steps of 10 hours at 1000°C or 1100°C. Understanding how Cs moves through the SiC layer will provide valuable insight into the kinetic mechanism of Cs diffusion in the SiC layer of the Gen IV TRISO fuel particle. If grain boundaries are a significant contributor to the diffusion of Cs it may be necessary to minimize grain boundary area through coarsening. Through discussion with the instrument technicians, the project is estimated to require about 84 hours of instrument time. The samples are presently ready for delivery at the first available opening in instrument booking.
Award Announced Date	2013-10-30T00:00:00
Awarded Institution	None
Facility	None
Facility Tech Lead	Yaqiao Wu
Irradiation Facility	None
PI	John Youngsman
PI Email	[email protected]
Project Type	RTE
RTE Number	439