Liu, Dong. Investigation of buffer densification using TRISO particles irradiated in PYCASSO project

Principal Investigator
First Name:
Last Name:
University of Bristol
Assistant Professor
Team Members:
Name: Institution: Expertise: Status:
Joshua Kane Idaho National Lab X-ray tomography characterization and segmentation Other
John Stempien Idaho National Laboratory TRISO particles shipping and characterization Other
Steven Knol NRG, the Netherlands Sample shipping and historical data Other
Experiment Details:
Experiment Title:
Investigation of buffer densification using TRISO particles irradiated in PYCASSO project
Describe the work that you are proposing in detail. Please include as many specifics as possible (e.g., dose, dose rate, ion energy, types of ions, beam line x-ray energy, irradiation temperature, analysis temperature, atmosphere, etc.):
The proposed experiment will use a Zeiss Versa 520 X-ray computed micro-tomography (XCT) system at the US Idaho National Laboratory to image two types of dedicated CEA TRISO particles (Kernel/Buffer (Buffer-1) and Kernel/Buffer/SiC (SiC-1)) from PYCASSO (PYrocarbon irradiation for Creep And Swelling/Shrinkage of Objects) irradiation program. PYCASSO irradiation took place in the High Flux Reactor (HFR) Petten, and were coordinated by NRG (The Netherlands). These particles were irradiated at about 1000C to two doses. For the XCT imaging, a comparable pixel size of 1.9-2 µm will be used for direct/complimentary measurements to previous NRG measurements on the other two types of CEA particles (Kernel/Buffer/PyC (PYC-1) and Kernel/Buffer/PyC/SiC (PyC-2)). The particles to be examined have a diameter of about 1.25 mm and thus two particles may be imaged per scan to maximize productivity. An energy of 120 keV will be used permitting adequate contrast while maintaining an efficient speed for data collection. These conditions will permit two scans per day. Therefore, for the first week, 20 particles can be imaged. The tried-and-tested sample handling procedure used at NRG will be adopted for this experiment. As the dimensions of these particles in unirradiated condition were previously measured, we will focus on the measurements of CEA Buffer-1 and SiC-1 at both irradiation doses. As such, 5 particles for each set of particle and dose will be imaged. For the second week of the experiment, 3 of the 5 particles from each set will be mounted and polished to Electron backscatter diffraction (EBSD) quality. This leaves 2 particles intact for future reference and incorporation into the NSUF library. The polished samples will be shipped back to the UK for post analysis using (1) EBSD, Raman spectroscopy and focused ion beam (FIB) digital image correlation method for evaluation of crystallite size/orientation, residual stresses and phase identification; (2) FIB lift out of transmission electron microscopy (TEM) foils will be made at the University of Bristol and then followed by high resolution TEM/STEM at the University of Oxford for irradiation damage characterization.
Technical Abstract
This project proposed here will make use of the TRISO particles irradiated in a unique programme – PYCASSO (PYrocarbon irradiation for Creep And Swelling/Shrinkage of Objects), to study the densification kinetics of the buffer and PyC layers excluding effects due to the presence of fuel, such as pressurization or chemical attack by fission products. Most ongoing programs focus on standard TRISO particles where multiple factors could influence the dimensional changes and fission product transportation/retention; this current project aims to separate these effect thereby contributes to the fundamental mechanistic understanding of buffer and PyC dimensional changes. Specifically, high resolution X-ray computed tomography will be adopted to capture the 3D microstructure of two types of particles (Kernel/Buffer and Kernel/Buffer/SiC) irradiated at 1000C to two doses (1.65x1025 n/cm2 and 2.05x1025 n/cm2). The thickness/radius of each layer will be subsequently derived from image segmentation. The results will be combined with the other two particles irradiated in the same program under the same conditions and have been previously characterized (Kernel/Buffer/PyC and Kernel/Buffer/PyC/SiC). This will allow us to (1) acquire first-hand information on the densification of the buffer layer after irradiation with and without PyC layer, and (2) assess the difference between unrestrained and restraint swelling of PyC and SiC. In addition, three particles of each type will be polished to reveal the cross-sections for post analysis using electron backscatter diffraction, Raman spectroscopy and transmission electron microscope to acquire information on the crystallite size/orientation of the SiC, residual stresses and irradiation damage in all layers. The outcome of the project will provide valuable input to the understanding of irradiation induced dimensional change in TRISO particles excluding the impact of fission products and pressurization to underpin the design and optimization of TRISO fuel.