Search Results (406)

Passive films that form on Alloy 600 and Alloy 690 during four hours in simulated Primary Water (PW) of Pressurized Water Nuclear Reactors (PWRs) at 320 °C were investigated by in situ surface-enhanced Raman spectroscopy (SERS). Similar tests conducted on unalloyed nickel, unalloyed chromium, and laboratory alloys of Ni-10Cr, Ni-20Cr, Ni-5Cr-8Fe, and Ni-10Cr-8Fe aided in assigning the peaks in the surface-enhanced Raman (SER) spectra of the passive films of Alloy 600 and Alloy 690. SERS indicates an inner layer (IL) of Cr₂O₃/CrOOH forms on both Alloy 600 and Alloy 690 and that Alloy 690’s IL was more protective against corrosion due to its greater resistance to ion transport. The outer layer (OL) of Alloy 600 consists of NiO and spinels, FeCr₂O₄—M(Cr,Fe)₂O₄. The OL of Alloy 690 contains no spinel. A comparison of SER spectra in 320 °C PWR PW to the spectra following cooling down to room temperature and after exposure to air indicates some differences between in situ films and ex situ films. Full article

Fault diagnosis in pressurized water reactor nuclear power plants faces the challenges of limited labeled data and severe class imbalance, particularly under Design Basis Accident (DBA) conditions. To address these issues, this study proposes a novel framework integrating three key stages: (1) feature selection via a signed directed graph to identify key parameters within datasets; (2) temporal feature encoding using Gramian Angular Difference Field (GADF) imaging; and (3) an improved Deep Subdomain Adaptation Network (DSAN) using weighted Focal Loss and confidence-based pseudo-label calibration. The improved DSAN uses the Hadamard product to achieve feature fusion of ResNet-50 outputs from multiple GADF images, and then aligns both global and class-wise subdomains. Experimental results show that, on the transfer task from the NPPAD source set to the PcTran-simulated AP-1000 target set across five DBA scenarios, the framework raises the overall accuracy from 72.5% to 80.5%, increases macro-F1 to 0.75 and AUC-ROC to 0.84, and improves average minority-class recall to 74.5%, outperforming the original DSAN and four baselines by explicitly prioritizing minority-class samples and mitigating pseudo-label noise. However, our evaluation is confined to simulated data, and validating the framework on actual plant operational logs will be addressed in future work. Full article

Cracks due to stress corrosion cracking in stainless steels are becoming a problem not only in boiling water reactors but also in pressurized water reactor nuclear plants. Stress improvement measures have been implemented mainly for large-bore welded piping, but in the case of small-bore welded piping, post-welding stress improvement measures are often not possible due to dimensional restrictions, etc. Therefore, knowing the actual welding residual stresses of small-bore welded piping regardless of reactor type is essential for the safe and stable operation of nuclear power stations, but there are only a limited number of examples of measuring the residual stresses. In this study, austenitic stainless steel pipes with an outer diameter of 100 mm and a wall thickness of 11.1 mm were butt-welded. The residual stresses were measured by the strain scanning method using neutrons. Furthermore, to obtain detailed residual stresses near the penetration bead where the maximum stress is generated, the residual stresses near the inner surface of the weld were measured using the double-exposure method (DEM) with hard X-rays of synchrotron radiation. A method using a cross-correlation algorithm was proposed to determine the accurate diffraction angle from the complex diffraction patterns from the coarse grains, dendritic structures, and plastic zones. A quantum beam hybrid method (QBHM) was proposed that uses the circumferential residual stresses obtained by neutrons and the residual stresses obtained by the double-exposure method in a complementary use. The residual stress map of welded piping measured using the QBHM showed an area where the axial tensile residual stress exists from the neighborhood of the penetration bead toward the inside of the welded metal. This result could explain the occurrence of stress corrosion cracking in the butt-welded piping. A finite element analysis of the same butt-welded piping was performed and its results were compared. There is also a difference between the simulation results of residual stress using the finite element method and the measurement results using the QBHM. This difference is because the measured residual stress map also includes the effect of the stress of each crystal grain based on elastic anisotropy, that is, residual micro-stress. Full article

Increasing the efficiency and capacity of nuclear power units is a promising direction for the development of power generation systems. Unlike thermal power plants, nuclear power plants operate at relatively low temperatures of the steam working fluid. Due to this, the thermodynamic efficiency of such schemes remains relatively low today. The temperature of steam and the efficiency of nuclear power units can be increased by integrating external superheating of the working fluid into the schemes of steam turbine plants. This paper presents the results of a thermodynamic analysis of thermal schemes of NPPs integrated with hydrocarbon-fueled plants. Schemes with a remote combustion chamber, a boiler unit and a gas turbine plant are considered. It has been established that superheating fresh steam after the steam generator is an effective superheating solution due to the utilization of heat from the exhaust gases of the GTU using an afterburner. Furthermore, there is a partial replacement of high- and low-pressure heaters in the regeneration system, with gas heaters for condensate and steam superheating after the steam generator for water-cooled and liquid-metal reactor types. An increase in the net efficiency of the hybrid NPP is observed by 8.49 and 5.11%, respectively, while the net electric power increases by 93.3 and 76.7%. Full article

Accurate mechanical property parameters constitute an indispensable guarantee for the accuracy of finite element simulations. Traditionally, uniaxial tensile tests are instrumental in acquiring the stress–strain data of materials during elongation, thereby facilitating the determination of the materials’ mechanical property parameters. By capitalizing on the digital image correlation (DIC) non-contact optical measurement technique, the entire test can be comprehensively documented using high-speed cameras. Subsequently, through in-depth analysis and meticulous numerical computations enabled by computer vision technology, the complete strain evolution of the specimen throughout the test can be precisely obtained. In this study, a comparison was made between the application of strain gauges and DIC testing systems for measuring the strain alterations during the tensile testing of 316L stainless steel, which serves as the material for the primary circuit pipelines of pressurized water reactor (PWR) nuclear power plants (NPPs). The data procured from these two methods were utilized as material mechanical parameters for finite element simulations, and a numerical simulation of the uniaxial tensile test was executed. The results reveal that, within the measuring range of the strain gauge, the DIC method generates measurement outcomes that are virtually identical to those obtained by strain gauges. Given its wider measurement range, the DIC method can be effectively adopted in the process of obtaining material mechanical parameters for finite element simulations. Full article

Fluid mechanical conditions are crucial for cavitation formation, and significantly influence chemical reactivity. This study investigates process conditions such as pressure, degassing, cavitation and reaction volume, and the sound emission of oxidative dye degradation by cavitation. For ensuring comparability and scalability, dimensionless similarity numbers aligned to the process were introduced. A further focus of the paper is reproducibility with corresponding guidelines. Measurements of dye degradation were carried out without additional chemicals. The oxidation process was assessed by the chemiluminescence of luminol. For this purpose, configurations with three nozzle sizes at different pressure differences were investigated. The generated cavitating jet was captured by imaging techniques and correlated to degradation. The most energy-efficient configuration was obtained by the smallest nozzle diameter of 0.6 mm at a pressure difference of 40 bar. Significant degassing occurred during cavitation. It was more pronounced with smaller nozzle diameters, correlating with higher degradation. Furthermore, discontinuous treatment methods can improve efficiency. Scaling to higher flow rates through multiple reactors in parallel proved more effective, compared to increasing the nozzle diameter or the pressure difference. For the same treated volume, two parallel reactors increased degradation by a factor of 1.35. The insights provide perspectives for optimizing jet cavitation reactors for water treatment. Full article

This study focuses on optimizing the Reverse Water Gas Shift (RWGS) reaction system using a membrane reactor to improve CO₂ conversion efficiency. A one-dimensional simulation model was developed using FlexPDE Professional Version 8.01/W64 software to analyze the performance of ZSM-5 membranes integrated with 0.5 wt% Ru-Cu/ZnO/Al₂O₃ catalysts. The results show that the membrane reactor significantly outperforms the conventional Packed Bed Reactor by achieving higher CO₂ conversion (0.61 vs. 0.99 with optimized parameters), especially at lower temperatures, due to its ability to remove H₂O and shift the reaction equilibrium selectively. Key operational parameters, including temperature, pressure, and sweep gas flow rate, were optimized to maximize membrane reactor performance. The ZSM-5 membrane showed strong H₂O selectivity, with an optimum operating temperature of around 400–600 °C. The problem is that many reactants permeate at higher temperatures. Subsequently, a Half-MPBR design was introduced. This design was able to overcome the reactant permeation problem and increase the conversion. The conversion ratios for PBR, MPBR, and Half-MPBR are 0.71, 0.75, and 0.86, respectively. This work highlights the potential of membrane reactors to overcome the thermodynamic limitations of RWGS reactions and provides valuable insights to advance Carbon Capture and Utilization technologies. Full article

In this study, plasma-activated water (PAW) was generated using a large-volume (5 L) plasma reactor with a quasi-stationary, water-cathode glow-type discharge in atmospheric pressure air. Tap water was activated up to 75 min. PAW exhibited high concentrations of long-lived reactive nitrogen species (RNSs), reaching 8 mM, which is between 4 and 26 times higher than those reported in previous studies. The reactor reached an RNS synthesis efficiency of 61 nmol/J and an RNS production rate of 526 μmol/min, both among the highest reported. PAW was evaluated on tomato and bell pepper. Seedling emergence was determined in a nutrient-free substrate. To assess plant growth, seedlings were transplanted into pots filled with either nitrogen-free or nutrient-rich substrate. PAW-irrigation significantly promoted seedling emergence and leaf expansion, especially in tomato plants. The plant growth-stimulating effects of PAW were more pronounced in nitrogen-free substrate: fresh weight of tomato and bell pepper increased up to 13.1-fold and 2.6-fold, respectively. In contrast, the effect on the nutrient-rich substrate was negligible. Tomato plants grown in the nitrogen-free substrate and irrigated with 75-min PAW reached a dry weight comparable to those grown in nutrient-rich substrate. PAW irrigation did not induce oxidative stress, as confirmed by malondialdehyde (MDA) levels and antioxidant enzyme activity. Full article

The reactor system has multivariate, nonlinear, and strongly coupled dynamic characteristics, which puts high demands on the robustness, real-time demand, and accuracy of the control strategy. Conventional control approaches depend on the mathematical model of the system being controlled, making it challenging to handle the reactor system’s dynamic complexity and uncertainties. This paper proposes a multi-variable coupled control strategy for a nuclear reactor steam supply system based on a Deep Deterministic Policy Gradient reinforcement learning algorithm, designs and trains a multi-variable coupled intelligent controller to simultaneously realize the coordinated control of multiple parameters, such as the reactor power, average coolant temperature, steam pressure, etc., and performs a simulation validation of the control strategy under the typical transient variable load working conditions. Simulation results show that the reinforcement learning control effect is better than the PID control effect under a ±10% FP step variable load condition, a linear variable load condition, and a load dumping condition, and that the reactor power overshooting amount and regulation time, the maximum deviation of the coolant average temperature, the steam pressure, the pressure of pressurizer and relative liquid level, and the regulation time are improved by at least 15.5% compared with the traditional control method. Therefore, this study offers a theoretical framework for utilizing reinforcement learning in the field of nuclear reactor control. Full article

A novel model was proposed for U-Tube Steam Generators in Pressurized Water Reactors to be utilized in dynamics and control studies. The steam generator was divided into 14 nodes and investigated by applying mass and energy conservation equations in differential form. A system of nonlinear differential equations was obtained. This equation system was numerically simulated using the Julia programming language through a fourth order Runge–Kutta method. Accurate values for thermodynamic properties were taken from the Coolprop library, eliminating the need to take constant values or linear interpolations. A three-element proportional and integral control was applied as the control system in the model. Changes in feedwater flow rate, steam outlet flow rate, primary inlet flow rate, feedwater inlet temperature and primary inlet temperature were investigated, and the response of the steam generator was simulated using the developed model. It was observed that the proposed model gives results for U-Tube Steam Generators comparable to those in the literature and that it can be used in dynamic model and control simulations. Full article

Hydrogen is a clean, non-polluting fuel and a key player in decarbonizing the energy sector. Interest in hydrogen production has grown due to climate change concerns and the need for sustainable alternatives. Despite advancements in waste-to-hydrogen technologies, the efficient conversion of mixed plastic waste via an integrated thermochemical process remains insufficiently explored. This study introduces a novel multi-stage pyrolysis-reforming framework to maximize hydrogen yield from mixed plastic waste, including polyethylene (HDPE), polypropylene (PP), and polystyrene (PS). Hydrogen yield optimization is achieved through the integration of two water–gas shift reactors and a pressure swing adsorption unit, enabling hydrogen production rates of up to 31.85 kmol/h (64.21 kg/h) from 300 kg/h of mixed plastic wastes, consisting of 100 kg/h each of HDPE, PP, and PS. Key process parameters were evaluated, revealing that increasing reforming temperature from 500 °C to 1000 °C boosts hydrogen yield by 83.53%, although gains beyond 700 °C are minimal. Higher reforming pressures reduce hydrogen and carbon monoxide yields, while a steam-to-plastic ratio of two enhances production efficiency. This work highlights a novel, scalable, and thermochemically efficient strategy for valorizing mixed plastic waste into hydrogen, contributing to circular economy goals and sustainable energy transition. Full article

At present, the operation control modes of pressurized water reactor (PWR) nuclear power plants in service mainly include Mode-A, Mode-G, and MSHIM. Mode-A is mainly applicable to base load operation and cannot realize load tracking. In the process of Mode-G load tracking, it is necessary to adjust boron, and it cannot realize load tracking without boron regulation. Although MSHIM implements unregulated boron load tracking, a large number of control rods are inserted into the core during base load operation, which reduces the safety margin and causes certain economic losses. In recent years, China National Nuclear Corporation Limited proposed the Mode-C operation control mode, which attempts to concentrate the advantages of the above operation mode and avoid its disadvantages. When Mode-C is adopted, only one set of control rods is inserted into the reactor core to complete the nuclear power plant control task for the base load and other operations that do not require frequent reactor power regulation. For load tracking and other operations requiring frequent reactor power regulation, control rods are used instead of adjusting soluble boron to control core reactivity. Reactivity compensation and power distribution control in the load-tracking process are completed through control rods. When Mode-C mode is adopted, the reactivity control method under base load and load tracking conditions is different from other mature operating modes. It is impossible to directly adopt the ready-made reactor power control system scheme, which brings challenges to the practical engineering application of Mode-C. To solve the above problems, based on the idea of single-variable automatic control and bivariable automatic control in Mode-C under different load demand conditions, this paper carries out research on the strategy of the reactor power control system and puts forward two specific control schemes. Through the control simulation program based on the one-dimensional core model, the simulation model of the control object and control system is established, and the closed-loop simulation verification of the control strategy is completed. The simulation results show that the designed reactor power control system can realize automatic control of the full power operating range and non-adjustable boron load tracking, reduce the operator’s burden, and meet the expected operation effect of the Mode-C operating mode. Full article

Hydrothermal carbonization (HTC) is a novel thermochemical process that turns biomass into hydrochar, a substance rich in carbon that has potential uses in advanced material synthesis, energy production, and environmental remediation. With an emphasis on important chemical pathways, such as dehydration, decarboxylation, and polymerization, that control the conversion of lignocellulosic biomass into useful hydrochar, this review critically investigates the fundamental chemistry of HTC. A detailed analysis is conducted on the effects of process variables on the physicochemical characteristics of hydrochar, including temperature, pressure, biomass composition, water ratio, and residence time. Particular focus is placed on new developments in HTC technology that improve sustainability and efficiency, like recirculating process water and microwave-assisted co-hydrothermal carbonization. Furthermore, the improvement of adsorption capacity for organic contaminants and heavy metals is explored in relation to the functionalization and chemical activation of hydrochar, namely through surface modification and KOH treatment. The performance of hydrochar and biochar in adsorption, catalysis, and energy storage is compared, emphasizing the unique benefits and difficulties of each substance. Although hydrochar has a comparatively high higher heating value (HHV) and can be a good substitute for coal, issues with reactor design, process scalability, and secondary waste management continue to limit its widespread use. In order to maximize HTC as a sustainable and profitable avenue for biomass valorization, this study addresses critical research gaps and future initiatives. Full article

This paper presents an experimental study comparing the aeration efficiencies of hyperbolic funnels and a cylindrical reactor, focusing on key parameters such as dissolved oxygen (DO) concentration, standard oxygen transfer rate (SOTR₂₀), and standard aeration efficiency (SAE). The unique geometry of the hyperbolic funnel induces a helical water flow, which expands the gas–liquid interfacial area within the water vortex, thereby enhancing aeration efficiency via vortex dynamics. The cylindrical reactor forms larger water “umbrellas” at its outlet due to increased internal water pressure, specifically optimizing the umbrella-driven aeration. The study also evaluated a three-funnel cascade system, demonstrating that a single funnel operating in the umbrella regime is more aeration-efficient than multiple funnels in cascade, as additional funnels reduce the SAE, due to the increased pumping height required. Further experiments using 3D-printed funnels investigated the influence of outlet diameter on flow rates and aeration efficiency. Our results indicated that larger outlet diameters allowed higher flow rates and umbrella sizes, yielding a superior aeration efficiency and outperforming all other reactors tested. The study also highlights the importance of funnel positioning relative to the water reservoir, which significantly influences both the SOTR₂₀ and SAE. For the reactor investigated, a height of 75 cm was optimal for balancing both parameters. Whereas the SOTR₂₀ values of the lab reactors were lower than those of commercial systems, due to the lower flow rates, the SAE values were notably high, surpassing those of mechanical aeration systems. Our findings suggest that hyperbolic funnels are a promising and highly efficient alternative for wastewater and groundwater aeration, with a strong potential for scalability. Full article

The global need for energy has risen sharply recently. A global shift to clean energy is urgently needed to avoid catastrophic climate impacts. Hydrogen (H₂) has emerged as a potential alternative energy source with near-net-zero emissions. In the African continent, for sustainable access to clean energy and the transition away from fossil fuels, this paper presents a new approach through which waste energy can produce green hydrogen from biomass. Bio-based hydrogen employing organic waste and biomass is recommended using biological (anaerobic digestion and fermentation) processes for scalable, cheaper, and low-carbon hydrogen. By reviewing all methods for producing green hydrogen, dark fermentation can be applied in developed and developing countries without putting pressure on natural resources such as freshwater and rare metals, the primary feedstocks used in producing green hydrogen by electrolysis. It can be expanded to produce medium- and long-term green hydrogen without relying heavily on energy sources or building expensive infrastructure. Implementing the dark fermentation process can support poor communities in producing green hydrogen as an energy source regardless of political and tribal conflicts, unlike other methods that require political stability. In addition, this approach does not require the approval of new legislation. Such processes can ensure the minimization of waste and greenhouse gases. To achieve cost reduction in hydrogen production by 2030, governments should develop a strategy to expand the use of dark fermentation reactors and utilize hot water from various industrial processes (waste energy recovery from hot wastewater). Full article