Journal
JOURNAL OF NUCLEAR MATERIALS
Volume 526, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.jnucmat.2019.151770
Keywords
Uranium molybdenum alloy (U-Mo); Zirconium nitride (ZrN); Microstructure characterization; Ion irradiation; Diffusion barrier coatings; Atomic layer deposition (ALD)
Funding
- U.S. Department of Energy, Office of Material Management and Minimization in the U.S. National Nuclear Security Administration Office of Defense Nuclear Nonproliferation [DE-AC02-06CH11357]
- DOE Idaho Operation Office Contract [DE-AC07-051D14517]
- MRSEC program at the Materials Research Center [NSF DMR-1121262]
- Nanoscale Science and Engineering Center at the International Institute for Nanotechnology [NSF EEC-0647560]
- State of Illinois, through the International Institute for Nanotechnology
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Zirconium nitride (ZrN) thin film deposited via thermal atomic layer deposition (ALD) has been recently chosen as a candidate technology for application of a diffusion barrier coating on the low enriched uranium alloy powder considered in the NNSA research reactor conversion program. Reported here is the first instance of using ALD for coating actinide materials. For this study, a modified ALD system was constructed to produce one micron thick zirconium nitride (ZrN) coating over spherical particulate of natural uranium-molybdenum (U-Mo) based fuel. The ALD system was designed to have a rotating drum system, with provisions for facilitating sequential exposures of chemicals such as tetrakis dimethyl amido zirconium (TDMAZr) and ammonia (NH3) in order to deposit ZrN. The ALD system was successful in developing a highly conformal ZrN coating covering every individual U-7Mo particle. This article describes the ZrN film synthesis details and reports the produced microstructure and composition of the ALD ZrN as deposited on fuel particulates. The as-fabricated coating was determined to have a nanocrystalline structure in the cubic-ZrN (cF8) phase. It exhibited a dense microstructure with adequate interfacial bonding. TEM-EELS characterization demonstrated that the coating contains a very low amount of oxygen impurity. To understand the potential microstructural evolution for ALD ZrN during reactor operation, an in-situ heavy ion (Kr) irradiation experiment was performed at the IVEM-Tandem facility. A total fluence of 7.5 x 1015 ions/cm(2) (similar to 10 dpa) was achieved, and apart from minor grain coarsening in the ALD ZrN coating, no significant radiation effects were observed. (C) 2019 Elsevier B.V. All rights reserved.
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