Search

Coating of zirconium-based substrates is a promising method to obtain accident-tolerant fuel claddings for light water reactors. In this study, CrSi-based coatings with varying Si content were deposited by multi-arc ion plating, and the effect of Si content on the oxidation behavior of the coatings in air at various temperatures (maximum 1160 °C) was investigated. The solid solution phase, formed by Si in CrSi coating, was seen to improve the oxidation performance of Cr. The nanocomposite structure in CrSiN coating can further improve the oxidation and stability of CrN. The results indicated that Si in CrSi-based coatings plays an effective role in the oxidation resistance of Zircaloy at high temperatures. Thus, these coatings could be used as potential accident tolerant fuel cladding materials for light water reactor applications.

The oxidation behaviors of Cr, Cr93.4Al6.6, Cr58.1Al41.9, and Cr34.5Al65.5 coatings, deposited by using multi-arc ion plating technology, at high temperature were studied. The weight gain, oxide thickness, morphology, and phase composition of the coatings before and after oxidation were analyzed in detail. The results show that there is an Al content window available for tuning the oxidation behaviors of the CrAl-based coatings. The Cr93.4Al6.6 coating is considered to be most protective and can effectively improve the high-temperature oxidation resistance of the substrate; whereas, too high an Al content has a harmful effect on the antioxidant properties of the coatings. The oxidation mechanism of Cr and CrAl coatings were also discussed.

From the past analyses of Core Disruptive Accidents (CDA) for sodium-cooled fast reactors, it has been recognized that with the assumption of very pessimistic conditions, a large-scale molten-fuel pool, which contains sufficient amount of fuel to achieve the prompt criticality by fuel compaction, might be formed. Due to the potential entrapment of liquid sodium into the fuel pool, local Fuel-Coolant Interaction (FCI) in the pool is considered to be one of the various initial factors resulting in such compactive fluid motions. To ascertain the mechanisms underlying this interaction more reliably, in our earlier publication a number of simulated experiments was carried out by releasing a given amount of liquid water into a molten pool (comprised of a low-melting-point alloy) using the PMCI (Pressurization characteristics in Melt-Coolant Interaction) facility recently developed at the Sun Yat-sen University. In this work, motivated to acquire more enhanced understanding, the effect of interaction mode on local FCIs is further investigated by adding new experimental data within the Melt-Injection (MI) mode. From detailed analyses, it is found that except the existence of a similar impact of melt temperature, much difference in the influence of other experimental parameters such as the liquid volume delivered, water subcooling along with the pool depth is observed. In addition, the performed analyses in this work also confirm that compared to previous Coolant-Injection (CI) mode, the mechanical energy conversion efficiency is much lower within the MI-mode condition. This work provides a large palette of beneficial experimental data and evidence for the better understanding of CDAs and improved verifications of fast reactor safety accident analysis codes in China.

Cr coatings were deposited by multi-arc ion plating under different gas pressures and bias potentials, and the oxidation behaviors of the coatings in air at various temperatures (max = 1060 °C) were investigated. The Cr coating structure could be modulated by varying the gas pressure and the bias potential, which affected its oxidation performance. The relationship among the gas pressure, the bias potential, and the oxidation performance was nonmonotonic. The formation of Cr2O3 caused a reduction in the oxidation weight gain of Zircaloy by 93.35%, indicating that our Cr coating played an effective role in the protection of Zircaloy at high temperatures.

With the aim of improving the oxidation resistance of fuel cladding in a light water reactor, CrN coating, which has good uniformity and compactness with an average thickness of about 13 μm, was deposited by multi-arc ion plating on a Zr alloy substrate heated to 400 °C. A series of comparative experiments of the oxidation resistances of the original (i.e., uncoated) and CrN-coated Zr alloys were performed in air atmosphere at high temperatures. The oxidation tests revealed that the CrN coating did not show any sign of cracking or shedding even after oxidation at 1160 °C. The weight gain of the Zr alloy decreased by 97.7% as a result of deposition of the CrN coating. The oxidation activation energy, calculated using Arrhenius plots, was obviously higher for the CrN-coated Zr alloy than for the uncoated Zr alloy. The results of transmission electron microscopy and X-ray diffraction analyses before and after the oxidation tests revealed that the oxidation product of CrN at high temperature was Cr2O3 and that the thickness of the oxide layer increased with an increase in oxidation temperature. Nanoindentation test results showed that the CrN coating also enhanced the mechanical properties of the Zr alloy. Even after oxidation at high temperature, the hardness and Young's modulus of the coating were significantly higher than those of the original Zr alloy. The CrN coating deposited by multi-arc ion plating exhibited excellent oxidation resistance and mechanical properties, which demonstrates its potential as a candidate material for accident-tolerant fuel cladding.

To develop a nuclear fuel cladding that has high tolerance under normal operating conditions and accident conditions, TiAlCrN coatings were deposited onto Zr substrates by multi-arc ion plating technique. After a corrosion test in static pure water at 360 °C and 18.5 MPa, the TiAlCrN coating showed no obvious spallation and had a weight gain of one order of magnitude less than that of the uncoated Zr sample. The decomposition and oxidation of the TiAlCrN coating at high temperature is an endothermic and exothermic reaction, respectively. Owing to the oxidation in the coating, the formed oxide layers reduce the oxygen penetration through the coating and also reduce the thickness of the zirconia layer from 300 μm to 10 μm at 1060 °C in air. This work lays the foundation for the next oxidation of TiAlCrN coating in high temperature steam, and demonstrates that TiAlCrN is a promising candidate material for the development of nuclear fuel cladding.

Friction and wear performance is one of the key mechanical properties of accident tolerant fuel cladding coatings. In this study, reciprocating sliding wear tests had performed on two types of CrAl and CrAlN coatings with two different Al content ratios and Zr-4. The coefficient of friction, wear depth, and abrasion loss were measured and compared. The results indicated that the CrAl-based coatings improve the wear behavior significantly and nitrogen has an obvious improvement on the wear resistance of the coating. The friction and wear performance was also studied in a water environment. The results show that the presence of water degrade the wear performance of Zr-4 and CrAl coatings but ameliorates the friction and wear performance of CrAlN coatings. The feasibility of depositing ATF coating on conventional Zr-4 substrates to mitigate the influence of grid-to-rod fretting was demonstrated.

Friction and wear resistance are important factors that affect the selection of accident-tolerant fuel coating materials. In this study, the wear behavior of a series of Cr-Nx coatings with different N contents was investigated using a reciprocating sliding tester. The coating morphology, change in the coefficient of friction during the friction and wear tests, and wear volume after the friction and wear tests, were characterized and discussed in detail. The results show that the Cr2N coating has better anti-friction and wear resistance behaviors than the Cr and CrN coatings under anhydrous and aqueous conditions. In addition, the water environment promoted the wear of the Zr-4 alloy and Cr coatings and inhibited the wear of the CrN and Cr2N coatings. The mechanisms of friction and wear were also discussed.

Studies on local fuel-coolant interaction in a molten pool are important for the improved evaluation of severe accidents that might be encountered for sodium-cooled fast reactors. To clarify the characteristics of this interaction, several years ago a series of simulated experiments was conducted at the Japan Atomic Energy Agency (JAEA) by delivering a given quantity of water into a molten pool formed with a low-melting-point alloy. In this work, motivated by acquiring more reliable database and knowledge, an improved experimental system has been developed recently at the Sun Yat-sen University. Experimental results from various conditions including much difference in water volume, melt temperature, water subcooling, initial water-lump shape along with melt depth, are discussed. It is found that the water volume, melt temperature, initial water-lump shape and melt depth are observable to have remarkable impact on the pressure-buildup characteristics while the role of water subcooling is less prominent. The observed consistent influence of water volume, melt temperature and water subcooling, as compared to previous studies at JAEA, indicates that despite the existence of some uncertainties, the statistical results recognized at JAEA might be overall valid. Owing to much enriched evidence, the present analyses suggest that the most probable reason leading to the limited pressurization as water volume increases for a given melt and water temperature, should be primarily due to the isolation effect of vapor bubbles at the melt-water interface.

The application of coating to cladding materials can potentially improve the accident-tolerant fuel cladding for light water reactors. In this study, oxidation behavior of five CrAl-based coatings containing different amounts of Al deposited onto Zr-4 alloy exposed to high-temperature air is investigated. The results demonstrate that pure Cr coating exhibits excellent oxidation resistance due to the formation of dense and continuous Cr2O3 oxide. By contrast, loose coatings with high Al contents correspond to poor oxidation resistance, which is related to the reaction between Zr and O. This paper proposes that the oxidation failure mechanisms of coatings depend on Al content. Data availability statement The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Friction and wear performance is a key issue in the development of accident tolerant fuel cladding coatings and worthy of attention. In this study, two types of CrSi and CrSiN coatings with two different Si content ratios were prepared via a multi-arc ion plating method, and their wear depth, wear volume, and coefficient of friction were compared in detail. The results show that the four CrSi-based coatings have better anti-friction and wear resistant properties than Zircaloy, and the CrSi-based coatings with high Si content have better friction and wear properties than the CrSi-based coatings with low Si content. In addition, the friction and wear properties of the CrSiN coatings are better than those of the CrSi coatings. This study also examined the friction and wear properties of the CrSi-based coatings in a water environment and after high temperature oxidation. The results show that water promotes the friction and wear of CrSi and Zr-4, but inhibits the friction and wear of the CrSiN coating. After high temperature oxidation, an appropriate increase in the Si content was found to improve the friction and wear resistance of the CrSi-based coatings.

In order to detect arc fault effectively, providing certain theoretical basis for arc fault detection technology, researching from the basic characteristics of arc, through establishing the static model of arc fault, analyzing the static volt-ampere characteristics of arc fault and the arc stability affected from resistance, the power supply voltage and volt-ampere characteristics; analyzing the dynamic characteristics of arc fault based on power frequency and phase characteristic of arc fault line voltage and current under power frequency half cycle.

In order to realize application of VSC-HVDC system on offshore wind farm, analyzing the principle and characteristics of VSC-HVDC system, Through its mathematical equivalent circuit, deduced active power and reactive power formulation. Based on the formulation analyzing three basic control mode of inverter. Combined with AC power and traditional HVDC system, analyzing advantaged performance of VSC-HVDC system. From the angle of technology and economy analyzing the feasibility of applicating VSC-HVDC system on offshore wind farm, and studied the relevant engineering cases.

In order to utilize the decoupling control strategy on VSC-HVDC, the dynamic mathematical models are set up at dq 0 rotating coordinate system. On the basis of mathematical models, decoupling controller of VSC is designed by adopting deviation decoupling strategy and the active power and reactive power can be controlled independently. Matlab/Simulink software is used simulating and analysing this designed system. The simulation results verify the correctness of the mathematical model and the reliability of the desgined controller.