Abstract
The use of single-crystal sapphire optical fibers has been considered to extend fiber-optic sensing to the extreme temperature (>1000 °C) environments encountered in nuclear applications. However, before these sapphire fiber–based sensors can be deployed, their optical transmission and dimensional stability (which impacts drift of some sensors) must be characterized under representative testing conditions. Data regarding the optical transmission of sapphire following high-dose neutron irradiation at temperatures >100 °C is extremely limited. This work provides measurements of optical density (i.e., attenuation) and directional dimensional changes in bulk single-crystal sapphire materials irradiated to a fast neutron fluence of 2.4 × 1021 n/cm2 (3.5 displacements per atom) at temperatures ranging from 95 to 688 °C. Optical density measured after irradiation at 95 and 298 °C showed ultraviolet and visible absorption bands corresponding to known defect centers and temperature trends that were generally consistent with previous ex situ and in situ measurements made at much lower neutron fluence. However, optical density measured after irradiation at 688 °C was as much as two orders of magnitude higher, indicating that the fundamental mechanism for radiation-induced attenuation changes at this irradiation temperature. Additional analysis and comparison with previous works suggest that the attenuation may result from void formation, leading to increased Rayleigh scattering losses in the material and increased swelling that would also result in drift of Bragg grating-based sensors in sapphire fibers. These results pose serious questions regarding the feasibility of sapphire fiber–based sensors for high-temperature nuclear applications.
| Original language | English |
|---|---|
| Article number | 153432 |
| Journal | Journal of Nuclear Materials |
| Volume | 559 |
| DOIs | |
| State | Published - Feb 2022 |
Funding
The initial conception and execution of the irradiation experiments presented herein were funded by the Laboratory Directed Research and Development Program of ORNL, managed by UT-Battelle, LLC, for the US Department of Energy (DOE). A portion of this research used the irradiation capabilities of HFIR, a DOE Office of Science User Facility operated by Oak Ridge National Laboratory (ORNL). Post-irradiation measurements were made using the ORNL Irradiated Materials Examination and Testing hot cell facility and the Low Activation Materials Development and Analysis (LAMDA) facility. The post-irradiation examination was supported by the DOE, Office of Nuclear Energy (DOE-NE) under DOE Idaho Operations Office Contract DE-AC07-051D14517 as part of a Nuclear Science User Facilities experiment. Curation and analysis of the post-irradiation measurement data was supported by the Nuclear Energy Enabling Technologies Program of DOE-NE. Jesse Werden, Alicia Raftery, and Kory Linton assisted in coordination of the post-irradiation examination. Travis Dixon performed the sample exchanges during the optical transmission measurements in LAMDA, and Keyou Mao performed the EDS measurements. Matt Kurley and Ercan Cakmak performed the XRD measurements. Adrian Schrell and Brandon Wilson provided helpful comments on the manuscript.
| Funders | Funder number |
|---|---|
| DOE-NE | DE-AC07-051D14517 |
| ORNL Laboratory Research and Development Program | |
| U.S. Department of Energy | |
| Office of Science | |
| Office of Nuclear Energy | |
| Oak Ridge National Laboratory |
Keywords
- Dimensional change
- Fiber-optic
- Optical
- Radiation
- Sapphire
- Transmission