NSUF 16-617: Evaluation of the effectiveness of PVD and ALD ZrN coating as a barrier to the formation of a UMo-Al interaction layer in dispersion fuels
One of the primary fuel types being investigated for conversion of reactors from high-enriched to low-enriched uranium fuels is a uranium-molybdenum alloy dispersed in an aluminum matrix (UMo-Al dispersion). A barrier to qualification of this fuel is the formation of an UMo-Al interaction layer (IL). This layer has poor fission gas retention, causing large bubbles to form at the interface of the IL and the matrix, leading to unacceptable swelling of the fuel plate. Coating the UMo fuel particles with a diffusion barrier (such as Si or ZrN) has been proposed as a possible IL formation mitigation solution. This study will focus on the addition of ZrN diffusion barrier coatings, with an emphasis on the coating fabrication method. Physical vapor deposition (PVD) has been used in the past(1), but cracking of the coating was observed upon examination of as-fabricated fuel plates. Atomic layer deposition (ALD) has been suggested as an alternative to PVD for application of the ZrN coating, as it offers well-controlled deposition and may provide better adhesion. In order to determine the relative performance of PVD and ALD ZrN coatings, three dispersion fuel plates were fabricated using identical manufacturing procedures. One plate was fabricated with uncoated UMo particles, one with ALD-coated UMo particles, and one plate was made with PVD-coated UMo particles. 1.7mm diameter disks were punched from each plate, and the cladding was removed from one side using traditional polishing techniques to a 0.1um finish to expose the fuel. These samples were then irradiated with 80MeV Xe ions at the ATLAS facility at Argonne National Laboratory. Due to the roughly Gaussian beam profile, three different doses were achieved in one experiment, so the dose-dependence of the radiation response of the fuel plate types can be analyzed. The FIB with EDS at MaCS will be used to fabricate site-specific samples from each 1.7mm disk to be examined that contain fuel, the coating (if present), and the matrix. FIB sample preparation will also enable the fabrication of a clean cross-section to examine with EDS to determine if Al was able to penetrate the coating, and if the coating is intact. Traditional polishing techniques could cause smearing (resulting in matrix Al in the fuel region) or cracking of the coating post-irradiation. The TEM with EDX at MaCS will be used to analyze the microstructure of each of these plates and to determine the local chemical composition of the sample. The local chemical composition will allow characterization of the IL (if present) for comparison to other studies (including in-pile), as well as determination if Al diffusion through the ZrN diffusion barrier has occurred. This experiment will determine the deposition method that results in the best-performing diffusion barrier (ALD or PVD), potentially leading to the eventual qualification of UMo-Al dispersion fuel. It is desired to complete this analysis within the next year to provide input for the upcoming EMPIRE experiment, which will irradiate similar fuel plates. This experiment will screen the ALD-coated particles for any unacceptable behavior prior to being tested in-reactor. (1)Leenaers, A. Surface-engineered low-enriched uranium-molybdenum fuel for research reactors. Universiteit Gent, Ghent, Belgium, 2014.
Additional Info
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| Abstract | One of the primary fuel types being investigated for conversion of reactors from high-enriched to low-enriched uranium fuels is a uranium-molybdenum alloy dispersed in an aluminum matrix (UMo-Al dispersion). A barrier to qualification of this fuel is the formation of an UMo-Al interaction layer (IL). This layer has poor fission gas retention, causing large bubbles to form at the interface of the IL and the matrix, leading to unacceptable swelling of the fuel plate. Coating the UMo fuel particles with a diffusion barrier (such as Si or ZrN) has been proposed as a possible IL formation mitigation solution. This study will focus on the addition of ZrN diffusion barrier coatings, with an emphasis on the coating fabrication method. Physical vapor deposition (PVD) has been used in the past(1), but cracking of the coating was observed upon examination of as-fabricated fuel plates. Atomic layer deposition (ALD) has been suggested as an alternative to PVD for application of the ZrN coating, as it offers well-controlled deposition and may provide better adhesion. In order to determine the relative performance of PVD and ALD ZrN coatings, three dispersion fuel plates were fabricated using identical manufacturing procedures. One plate was fabricated with uncoated UMo particles, one with ALD-coated UMo particles, and one plate was made with PVD-coated UMo particles. 1.7mm diameter disks were punched from each plate, and the cladding was removed from one side using traditional polishing techniques to a 0.1um finish to expose the fuel. These samples were then irradiated with 80MeV Xe ions at the ATLAS facility at Argonne National Laboratory. Due to the roughly Gaussian beam profile, three different doses were achieved in one experiment, so the dose-dependence of the radiation response of the fuel plate types can be analyzed. The FIB with EDS at MaCS will be used to fabricate site-specific samples from each 1.7mm disk to be examined that contain fuel, the coating (if present), and the matrix. FIB sample preparation will also enable the fabrication of a clean cross-section to examine with EDS to determine if Al was able to penetrate the coating, and if the coating is intact. Traditional polishing techniques could cause smearing (resulting in matrix Al in the fuel region) or cracking of the coating post-irradiation. The TEM with EDX at MaCS will be used to analyze the microstructure of each of these plates and to determine the local chemical composition of the sample. The local chemical composition will allow characterization of the IL (if present) for comparison to other studies (including in-pile), as well as determination if Al diffusion through the ZrN diffusion barrier has occurred. This experiment will determine the deposition method that results in the best-performing diffusion barrier (ALD or PVD), potentially leading to the eventual qualification of UMo-Al dispersion fuel. It is desired to complete this analysis within the next year to provide input for the upcoming EMPIRE experiment, which will irradiate similar fuel plates. This experiment will screen the ALD-coated particles for any unacceptable behavior prior to being tested in-reactor. (1)Leenaers, A. Surface-engineered low-enriched uranium-molybdenum fuel for research reactors. Universiteit Gent, Ghent, Belgium, 2014. |
| Award Announced Date | 2015-12-16T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Laura Jamison |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 617 |