Kinetics of irradiation defect annealing and thermal conductivity recovery in silicon carbide at high temperature

Principal Investigator
Name:
Nicholas Brown
Email:
[email protected]
Phone:
(208) 526-6918
Team Members:
Name: Institution: Expertise: Status:
N/A
Yutai Katoh ORNL Provide samples, expert in ceramic materials in extreme environments and radiation effects on ceramic materials Other
Experiment Details:
Experiment Title:
Kinetics of irradiation defect annealing and thermal conductivity recovery in silicon carbide at high temperature)
Work Description:
The objective of this project is to enhance understanding of the annealing of irradiation induced defects in high purity and sintered SiC samples at high temperatures. Under neutron irradiation the thermal conductivity of SiC degrades significantly, and within a certain temperature range (<900 oC) saturates at a nearly constant temperature-dependent value. This phenomenon has been consistently observed for both high purity variants (e.g. chemical vapor deposition [CVD] SiC) and lower purity sintered variants, though to different extents. Although it is well known that the irradiation-induced defects anneal out at high temperatures, the kinetics of the defect annealing processes is not well known. No prior efforts in the literature focus on the kinetics of irradiation annealing due to neutron irradiation and the resulting thermal conductivity recovery under temperature ramps in environments and at temperatures relevant for fission systems. This effort will aim to irradiate both high purity CVD SiC and lower purity sintered NITE SiC. The existing irradiated samples identified both exhibit strong impact on the thermal conductivity, which saturates at doses greater than 1 DPA. The SiC samples that will be used in this work have already been irradiated. The samples cover both high purity and sintered SiC variants. The samples are disks that will be subjected to temperature ramps and used for thermal diffusivity measurement. The specific samples are: Specimen 1: CVD SiC (6mm disc 0.6mm thick), ID: CVD4, Rabbit ID: IMR3 Specimen 2: NITE SiC (Al-Ce-Zr-O additive) (6mm disc 0.5mm thick), ID: 64, Rabbit ID: IMR4 Irradiation temperature: nominal 200oC for CVD, actual 230oC for NITE Dose: 1.97E25 n/m2 (0.1MeV >E), 1.97dpa for both The irradiated SiC samples (6 mm discs) will be subjected to thermal ramps to higher temperatures in a stepwise or isothermal manner. Thermal diffusivity will be measured during these temperature ramps in the absence of irradiation to simulate accident conditions. These properties will be used to determine the kinetics of the defect annealing in irradiated SiC and provide accurate values for thermal conductivity under these transient scenarios.
Abstract
The objective of this project is to enhance understanding of the annealing of irradiation induced defects in high purity and sintered SiC samples at high temperatures. Under neutron irradiation the thermal conductivity of SiC degrades significantly, and within a certain temperature range (<900 oC) saturates at a nearly constant temperature-dependent value. This phenomenon has been consistently observed for both high purity variants (e.g. chemical vapor deposition [CVD] SiC) and lower purity sintered variants, though to different extents. Although it is well known that the irradiation-induced defects anneal out at high temperatures, the kinetics of the defect annealing processes is not well known. No prior efforts in the literature focus on the kinetics of irradiation annealing due to neutron irradiation and the resulting thermal conductivity recovery under temperature ramps in environments and at temperatures relevant for fission systems. This effort will aim to irradiate both high purity CVD SiC and lower purity sintered NITE SiC. The existing irradiated samples identified both exhibit strong impact on the thermal conductivity, which saturates at doses greater than 1 DPA. The SiC samples that will be used in this work have already been irradiated.
Book / Journal Publications

"Fully Ceramic Microencapsulated fuel in prismatic high-temperature gas-cooled reactors: Sensitivity of reactor behavior during design basis accidents to fuel properties and the potential impact of the SiC defect annealing process" Takaaki Koyanagi, Yutai Katoh, Kurt Terrani, Nicholas Brown, Nuclear Engineering and Design 345 2019 125-147 Link