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| 2. |
- Lundin, Daniel, et al.
(författare)
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Transition between the discharge regimes of high power impulse magnetron sputtering and conventional direct current magnetron sputtering
- 2009
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Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 18:4
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Tidskriftsartikel (refereegranskat)abstract
- Current and voltage have been measured in a pulsed high power impulse magnetron sputtering (HiPIMS) system for discharge pulses longer than 100 mu s. Two different current regimes could clearly be distinguished during the pulses: (1) a high-current transient followed by (2) a plateau at lower currents. These results provide a link between the HiPIMS and the direct current magnetron sputtering (DCMS) discharge regimes. At high applied negative voltages the high-current transient had the characteristics of HiPIMS pulses, while at lower voltages the plateau values agreed with currents in DCMS using the same applied voltage. The current behavior was found to be strongly correlated with the chamber gas pressure, where increasing gas pressure resulted in increasing peak current and plateau current. Based on these experiments it is suggested here that the high-current transients cause a depletion of the working gas in the area in front of the target, and thereby a transition to a DCMS-like high-voltage, lower current regime.
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| 3. |
- Chen, Jiaxin, et al.
(författare)
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Microstructures of oxide films formed in alloy 182 BWR core shroud support leg cracks
- 2018
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Ingår i: Miner. Met. Mater. Ser.. - Cham : Springer International Publishing. - 9783319684536 ; Part F11, s. 417-431
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Konferensbidrag (refereegranskat)abstract
- This paper contributes to a TEM examination on the oxide films formed at three locations along a crack path in Alloy 182 weld from a BWR core shroud support leg, namely, the crack mouth, the midway between the mouth and the crack tip, and the crack tip. In the crack mouth the oxide film was approximately 1.6 μm in thickness and consisted of relatively pure NiO. The midway oxide film was mainly a nickel chromium oxide with a film thickness of 0.3 μm. At the crack tip the oxide film was a nickel chromium iron oxide with a film thickness of 30 nm. In all studied locations the main oxides had the similar rocksalt structure and the cracks were much wider than the thicknesses of the oxide films. It probably suggests that the corroded metal was largely dissolved into the coolant. The different dissolution rates of nickel, chromium and iron cations in the oxide films are clearly displayed with the compositions of the residual oxides. The oxide stability under different redox potentials along the crack path is briefly discussed.
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| 4. |
- Chen, Jiaxin, et al.
(författare)
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Microstructures of oxide films formed in alloy 182 bwr core shroud support leg cracks
- 2019
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Ingår i: Proceedings of the 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors. - Cham : Springer International Publishing. - 9783030046385 - 9783030046392 - 9783319515403 - 9783319651354 - 9783319728520 - 9783319950211 ; , s. 1633-1647
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Konferensbidrag (refereegranskat)abstract
- This paper contributes to a TEM examination on the oxide films formed at three locations along a crack path in Alloy 182 weld from a BWR core shroud support leg, namely, the crack mouth, the midway between the mouth and the crack tip, and the crack tip. In the crack mouth the oxide film was approximately 1.6 μm in thickness and consisted of relatively pure NiO. The midway oxide film was mainly a nickel chromium oxide with a film thickness of 0.3 μm. At the crack tip the oxide film was a nickel chromium iron oxide with a film thickness of 30 nm. In all studied locations the main oxides had the similar rocksalt structure and the cracks were much wider than the thicknesses of the oxide films. It probably suggests that the corroded metal was largely dissolved into the coolant. The different dissolution rates of nickel, chromium and iron cations in the oxide films are clearly displayed with the compositions of the residual oxides. The oxide stability under different redox potentials along the crack path is briefly discussed.
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| 8. |
- Patnaik, Sobhan, et al.
(författare)
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Crystallographic characterization of U 2 CrN 3 : A neutron diffraction and transmission electron microscopy approach
- 2023
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Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 35
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Tidskriftsartikel (refereegranskat)abstract
- In this study, neutron diffraction and transmission electron microscopy (TEM) have been implemented to study the crystallographic structure of the ternary phase U2CrN3 from pellet to nano scale respectively. Recently microstructural evaluation of this ternary phase has been performed for the first time in pellet condition, overcoming the Cr evaporation issue during the conventional sintering process. In this work for the first time, the crystallographic structure of the ordered ternary U2CrN3 phase, stabilized in pellet condition, has been obtained by implementing neutron diffraction. For this study, pellets of the composite material UN with 20 vol% CrN were fabricated by powder metallurgy by mixing UN and CrN powders followed by Spark Plasma Sintering (SPS). TEM was used to investigate the nanoscale structure with a thin lamella of the order of 100–140 nm produced by focused ion beam (FIB). The neutron data revealed the phase composition of the pellet to be primarily 54(8) wt.% U2CrN3, in good agreement with the stoichiometry of starting reagents (UN and CrN powder) and metallographic analysis. Neutron data analysis confirms that all the crystallographic sites in U2CrN3 phase are fully occupied reinforcing the fully stoichiometric composition of this phase, however, the position of the N at the 4i site was found to be closer to the Cr than previously thought. TEM and selected area electron diffraction rendered nano-level information and revealed the presence of nano domains along grain boundaries of UN and U2CrN3, indicating a formation mechanism of the ternary phase, where the phase likely nucleates as nano domains in UN grains from migration of Cr.
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| 9. |
- Senis, Lorenzo, et al.
(författare)
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Feasibility study of gamma-ray micro-densitometry for the examination of nuclear fuel swelling
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Nuclear fuel undergoes several thermo-mechanical changes during irradiation in a nuclear reactor, such as change of density, caused by solid and gaseous swelling. This affects the heat transport within the pellet and, when leading to the pellet-cladding gap closure, it also affects the gap conductance, causing stress in the cladding. The density of irradiated fuel pellets can be measured in post-irradiation examination using several methods. In this work, a feasibility study was made using the gamma-ray transmission micro-densitometry technique. This is based on the comparison of two intensity measurements, with and without a sample with well-characterized thickness. Using a collimated source, a local examination of the density can be performed, scanning a pellet slice radially. The proposed technique aims to obtain a spatial resolution of cca. 100 microns. In this work, the parameters of the setup, such as the source activity, detector counting time, slit dimensions, collimator length, and sample thickness, are used to predict detector efficiency and expected count rates. The obtainable precision of the density is assessed by first-order uncertainty propagation of counting errors in the gamma-ray detection to the density estimate. A collimator design was presented that achieves a reasonable compromise between time requirements, precision, and spatial resolution. The sensitivity of the performance to set-up parameters was investigated. In addition, a realistic setup was modeled in MCNP6 for validation of the peak count-rate, and to ensure that the total spectrum count-rate is within typical throughput capabilities of HPGe detectors. The MCNP model was also used to confirm that the assumed attenuation law is valid in a relevant geometry, and to assess the spatial resolution, using the 10-90% edge spread of an Edge Spread Function. It is concluded that fuel density can be determined with <1 % precision, using a 100-micron wide slit, and 1 hour of measurement.
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| 10. |
- Senis, Lorenzo, et al.
(författare)
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Performance evaluation of a novel gamma transmission micro-densitometer for PIE of nuclear fuel
- 2023
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Ingår i: Annals of Nuclear Energy. - : Elsevier. - 0306-4549 .- 1873-2100. ; 187
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Tidskriftsartikel (refereegranskat)abstract
- Collimated Gamma Transmission Micro-Densitometry (GTMD) is a novel technique proposed to investigate local density variations of nuclear fuel in PIE, with a high spatial resolution. In this work, the first experimental tests of a gamma micro-densitometer are presented and the performance is characterized. The experimental procedures are described, including the aligning process and the calibration methodology. The results demonstrated that for the calibration samples with a thickness above 5 mm, a local density was obtained with a maximum discrepancy of about 2% and a spatial resolution of about 280 µm. The setup was used for the first test on an irradiated ADOPTTM fuel pellet slice. From the measurement, an average bulk density of about 9.58 g/cm3 was calculated and local density features were observed, possibly related to rim effects or the presence of local cracks. The information acquired also presented valuable information for possible improvements in the setup’s performance.
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| 11. |
- Topping, Matthew, et al.
(författare)
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The effect of iron on dislocation evolution in model and commercial zirconium alloys
- 2018
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Ingår i: ASTM Special Technical Publication. - 0066-0558. ; STP 1597, s. 796-822
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Konferensbidrag (refereegranskat)abstract
- Although the evolution of irradiation-induced dislocation loops has been well correlated with irradiation-induced growth phenomena, the effect of alloying elements on this evolution remains elusive, especially at low fluences. To develop a more mechanistic understanding of the role iron has on loop formation, we used state-of-the-art techniques to study a proton-irradiated Zr-0.1Fe alloy and proton- and neutron-irradiated Zircaloy-2. The two alloys were irradiated with 2-MeV protons up to 7 dpa at 350°C and Zircaloy-2 up to 14.7 × 1025n • m-2, approximately 24 dpa, in a boiling water reactor at approximately 300°C. Baseline transmission electron microscopy showed that the Zr3Fe secondary-phase particles in the binary system were larger and fewer in number than the Zr (Fe, Cr)2and Zr2(Fe, Ni) particles in Zircaloy-2. An analysis of the irradiated binary alloy revealed only limited dissolution of Ze3Fe, suggesting little dispersion of iron into the matrix, while at the same time a higher 〈a〉-loop density was observed compared with Zircaloy-2 at equivalent proton dose levels. We also found that the redistribution of iron during irradiation led to the formation of iron nanoclusters. A delay in the onset of 〈c〉-loop nucleation in proton-irradiated Zircaloy-2 compared with the binary alloy was observed. The effect of iron redistributed from secondary-phase particles because of dissolution on the density and morphology of 〈a〉 and 〈c〉 loops is described. The implication this may have on irradiation-induced growth of zirconium fuel cladding is also discussed.
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