Hydrogen storage based on metal hydrides (MH) demonstrates volumetric hydrogen storage capacity far exceeding that of traditional gaseous or liquid hydrogen storage methods, thereby effectively improving the energy density and economic feasibility of hydrogen storage systems. However, the relatively low thermal conductivity of metal hydride materials requires the introduction of high thermal conductivity heat sinks to further improve the heat transfer performance of MH. In this study, topological optimization was performed on the fin structure within the MH reactor, and topological optimization methods suitable for different optimization objectives and directions were proposed. Additionally, the effects of various structures on reactor performance were further analyzed.The results indicate that, in comparison to the topology optimized for minimizing average temperature, the topology optimized for minimizing thermal compliance features a more uniform distribution and a faster hydrogen absorption rate, with the maximum hydrogen absorption rate increased by 7.07%. Relative to the axial topological structure, the radial topological structure is uniformly and densely distributed in the MH bed, which is more conducive to heat dissipation and hydrogen absorption, reducing the overall hydrogen absorption time by 34.03%. Compared with the basic rectangular fin structure, the optimal-performing radial topological structure has a heat transfer area increased by 2.08 times, demonstrating superior heat transfer performance and greater facilitation of hydrogen absorption, with the overall hydrogen absorption time shortened by 23.64%. Finally, after analyzing the fractal characteristics of the topological structures, it was found that these topological structures have fractal dimensions similar to the optimal solutions found in nature.

Unstable steam jet condensation may cause strong pressure oscillation. Transient numerical simulation is conducted on unstable steam jet for round and obround side-hole spargers. The model effectively captures differences in main frequency of the two type holes. The relationship between pressure fluctuation characteristics in fluid domain and bubble evolution process is discussed. The pressure peak occurs near the secondary bubble collapse location. Under the same thermal conditions, obround holes produce a time-averaged bubble volume that is 1.22 times larger, a time-averaged penetration depth that is 0.96 times that of round holes, and condensation oscillation periods that are 1.16 times longer. The pressure distribution in fluid domain is reconstructed through data of 112 pressure monitoring points. A pressure peak area exists in the fluid domain, and the magnitude of pressure peak at each position in domain is almost inversely proportional to distance from position where the secondary bubble collapses. Position of the maximum pressure peak on sparger surface occurs at a distance of 0.5-1.5 times diameter from the hole edge. With increase of steam mass flux and water subcooling, the maximum peak pressure in domain increases, meanwhile, the pressure impact on sparger wall also increases.

Jet condensers, characterized by their compact design, low temperature differential, and cost-effectiveness. Two experimental facilities were set up to analyze the flow dynamics and heat transfer characteristics of jet condensers. Cold-state experiments primarily investigated the impact of water flow rate, nozzle angle, and nozzle diameter on the liquid film flow dynamics within the jet condenser. Hot-state experiments were designed to explore the influence of cooling water flow rate, air leakage, and steam velocity on the condenser heat transfer characteristics. The findings suggest similar patterns in the effects of flow rate and nozzle angle on the liquid film area within the condenser. As these variables increase, the liquid film area initially expand, followed by a peak and subsequent decline. Additionally, as the flow rate increases, the ideal nozzle angle for each flow rate progressively diminishes. It is recommended to use larger nozzles for higher flow rates and smaller nozzles for lower flow rates. The post-impact fluid zone following jet collision with a baffle can be divided into three distinct regions: liquid film, hydraulic jump, and droplet. In hot-state experiments, the condenser heat transfer efficiency demonstrates a linear growth with increasing cooling water flow rate. Notably, the temperature at the edges of the liquid film stabilizes around 87.5 degrees C. An increase in air leakage rate significantly reduces the heat transfer effectiveness of the condenser. In contrast, the steam velocity has minimal impact on heat transfer efficiency.

To investigate the effect of seawater intrusion on steam jets under accident conditions in nuclear power plants, experiments were conducted to study the flow regime evolution and pressure oscillation characteristics of steam jets under different salinities (0%o to 35%o). The experimental data reveal that altering salinity does not appreciably alter the regime transition boundaries or the dominant frequency of pressure oscillations. However, salt ions inhibit bubble coalescence, resulting in a denser small bubble swarm in seawater. Under the Chugging regime, the pressure oscillation intensity and MPa-level peaks of seawater and freshwater jets are similar. Under the Condensation Oscillation regime, the pressure oscillation inside the nozzle is similar between the two, whereas the oscillation in the pool depends on the small bubble swarm: at low water temperatures, higher salinity leads to stronger oscillation; at high water temperatures, the oscillation peak in the freshwater pool is much higher than that in the seawater pool. Steam mass flux and water temperature affect the dominant frequency in opposite ways (the former raising it, the latter lowering it), with salinity having only a negligible effect. This study confirms that the macroscopic condensation mechanisms of seawater and freshwater are consistent, providing a basis for employing seawater cooling under extreme conditions; the higher oscillation peaks observed in low-temperature seawater under the Condensation Oscillation regime suggest that fatigue assessment of relevant systems should use data obtained under seawater conditions.

Natural convection finned heat sinks are widely utilized in the nuclear field. Enhancing the convective heat transfer capability of finned heat sinks is a crucial measure to ensure reactor safety and improve efficiency. To enhance the heat dissipation capability of the heat sink, this study utilized a natural convection substitution model and the optimality criterion method for topology optimization design on traditional fin heat sink. Additionally, fractal biomimicry principles were employed to analyze the shape of the optimized structure. This study conducted topology optimization on the heat sink structure with different volume constraints. The heat transfer performance of the optimized structures under different volume constraints was analyzed through numerical simulations. The heat sink structure after topology optimization presents a leaf vein pattern, with the fins extending from the heat source gradually becoming thinner and displaying fractal features at the end of the fins. Additionally, small fins grow on the surface of the fins to further enhance convective heat transfer. Numerical simulation analysis shows that compared to traditional heat sink, the leaf vein-like heat sink is more conducive to heat conduction and convective heat transfer. Finally, the box-counting method was used to further analyze the fractal characteristics of the optimized fins, verifying their similarity to plant leaf veins, and thus demonstrating that the topology optimization structure approaches an optimal solution found in nature.

Steam-seawater jet can be one of the main solutions for reactor pressure control after an accident in a marine nuclear power plant. However, there is a lack of research on the phenomenon of steam immersion jet under seawater conditions, and the pressure oscillation characteristics of steam low-velocity immersion jet under seawater conditions are still unclear. Through experimental research, the differences between the typical dynamic pressure signal, pressure oscillation intensity, pressure oscillation amplitude and pressure oscillation frequency of low-velocity steam jet condensation in seawater and low-velocity steam jet condensation in freshwater are compared and analyzed. The results show that there are differences between the steam-seawater jet and the steam-freshwater jet, especially the pressure oscillation amplitude in the pool, and the pressure oscillation amplitude in the steam-seawater jet is much smaller than that of the steam-freshwater jet under higher water temperature. The research in this study is helpful to understand and grasp the pressure oscillation characteristics of steam-seawater jet.

Current advanced pressurized water reactors widely employ passive containment cooling systems (PCCS) as critical measures to protect containment integrity. However, for certain reactor types, spatial constraints on equipment arrangement often necessitate long horizontal pipelines in their PCCS configurations. To investigate the closed-valve startup characteristics of PCCS with long-horizontal-section structures, a computational model for PCCS startup behavior was established using the system analysis code, and its applicability for simulating PCCS startup processes was validated against experimental data. Additionally, startup characteristics under different valve opening conditions were calculated. Two flow rate surges were observed during the closed-valve startup phase of PCCS. The first surge resulted from density differences between the heat exchanger and downcomer section, while the second surge was caused by flashing of saturated water from the heat exchanger in vertical piping. Comparative analysis revealed that lower containment outlet temperatures at valve opening prolonged the single-phase startup phase and shortened the two-phase flashing startup phase. Investigations into the effects of containment temperature and pressure on closed-valve startup characteristics demonstrated that the single-phase startup phase gradually diminishes as internal containment temperature and pressure increase.

During the operation of nuclear power plants (NPP), the occurrence of severe accidents and critical equipment failures poses a significant threat to plant safety, creating stringent requirements for the accuracy and real-time performance of accident diagnosis and fault monitoring systems. Principal Component Analysis (PCA), as an effective dimensionality reduction algorithm, can extract key features from data, effectively reduce noise, and improve data processing efficiency. Consequently, PCA has been widely applied in recent years in nuclear power plant accident diagnosis and equipment fault monitoring. This paper systematically reviews the current applications of PCA techniques and their variants in NPP, focusing on the critical role of PCA and its variants in accident diagnosis and fault monitoring. Additionally, the paper explores the advantages of combining PCA with other machine learning techniques, such as Support Vector Machines (SVM) and neural networks, analyzing how these combinations enhance accuracy and robustness in accident diagnosis and fault monitoring. Finally, the paper summarizes the achievements and challenges of current PCA applications in nuclear plant diagnostic and monitoring systems and proposes potential future research directions.

Condensation oscillation heat transfer characteristics of steam jets are studied by using transient threedimensional CFD method under different steam mass flux, water subcooling, through round/obround side-hole spargers. Compared with round hole, obround hole has a longer condensation oscillation occurrence period and a larger external interface area, 11.59 % larger than that of the round hole, while the external heat exchange coefficient is slightly lower by 2.02 %. The change of interface area plays a dominant role in the influence on steam condensation rate. The maximum local heat transfer coefficient occurs at the neck of main bubble during necking stage, while the maximum average heat transfer coefficient occurs when the secondary bubble just detaches. The external time-averaged average heat transfer coefficients outside spargers are much higher than those inside spragers, the former ranges from 0.1 MW to 0.14 MW, while the later ranges from 0.017 MW to 0.05 MW. With increase of steam mass flux and decrease of water subcooling, heat transfer coefficients outside sparger increase while the internal heat transfer coefficients decrease. Meanwhile, external interface area increases, while the internal interface area basically does not change with variation of thermal parameters and mainly depends on the internal dimensions of sparger chamber. Furthermore, the proportion of condensation amount inside the sparger to total condensation amount gradually decreases. Within calculation parameters, the proportion of internal condensation is 5 % to 25 %.

Containment is the last physical barrier for nuclear power plant to prevent the escape of radioactive materials, and the containment tightness is an important index for the evaluation of containment performance. Accurate and effective containment evaluation is crucial for nuclear safety of nuclear power plant. This paper uses CFD numerical simulation calculation method to simulate the leakage rate test process, analyzes the influence of leakage location, leakage port size and other factors on the temperature field in the shell, studies the influence of the selection of pressure measurement points at different heights on the calculation of leakage rate, and aims at the non-adiabatic containment under the influence of external environment. The leakage rate values obtained by weighted method, volumetric average method and finite element analysis are compared and analyzed, and the quantitative error of leakage rate calculation by finite measuring points is evaluated. The results show that within the permissible range of containment leakage rate, the leakage location and the size of the leakage port have little influence on the temperature field in the containment. The difference of pressure measurement points in the height direction has a certain effect on the calculated value of dry air quality in the shell, but has little effect on the calculated value of leakage rate. Even if there is no internal heat source in the containment, the deviation value of leakage rate calculated by using finite temperature measuring points will increase significantly if it is greatly affected by the change of external environment temperature.

High-efficiency thermal layouts of high-heat-flux nuclear cold plates require simultaneous temperature uniformity and low hydraulic loss. Although topology optimization has been extensively used in liquid-cooled microchannel heat sinks, the effect of symmetric and non-symmetric inlet-outlet configurations on the thermal equalization and pressure drop in nuclear cooling systems has not been fully investigated. In this study, a densitybased multi-objective topology optimization approach is proposed for liquid-cooled microchannel cold plates. The proposed objective function optimizes the thermal objective Jth and the flow-related hydraulic dissipation objective Jf. We consider five different inlet-outlet configurations with the same constraints, two symmetric inletoutlet models (SM1 and SM2), and three non-symmetric inlet-outlet models (M3, M4, and M5). SM stands for a symmetric inlet-outlet model, and M for a non-symmetric inlet-outlet model. The optimization is carried out with a weighting factor of Wt = 0.5, a constant fluid volume fraction of Vf = 0.5, a heat input of Qin = 500 W, and Reynolds numbers Re ranging from 50 to 150. The findings demonstrate that M5 (with three inlets and one outlet) achieves the best thermal performance, with maximum reductions in thermal non-uniformity (52.4%), thermal resistance (52.7%), and increases in the Nusselt number (110.5%) compared to the baseline SM1. However, the best hydraulic performance was achieved with M4, which decreases the pressure drop by up to 64% and the flow resistance by up to 71.3%. Overall, M5 is preferred when thermal equalization is the primary design requirement, whereas M4 provides a better thermal-hydraulic compromise when pumping loss is critical. The results demonstrate that inlet-outlet configuration strongly affects flow redistribution, hotspot mitigation, and thermal-hydraulic trade-off in nuclear microchannel cold plates.

Topology optimization of dual-fluid heat exchangers offers the potential to discover channel configurations that fundamentally outperform conventional geometries, yet the systematic influence of key parameters on channel morphology and thermal performance remains incompletely characterized. This study presents a density-based topology optimization framework for two-dimensional dual-fluid heat exchangers, coupling Brinkman-penalized Navier-Stokes equations with a convective-conductive energy equation via the RAMP interpolation scheme. A comprehensive parametric investigation examines the initial design variable, RAMP stiffness parameter (q), Peclet number (Pe), inlet pressure, and flow arrangement. Results reveal a critical, discontinuous morphological transition between q = 0.1 and q = 0.3, where the topology shifts irreversibly from a multi-bend serpentine configuration (η = 52.4%) to a single-arch design (η = 24.0%). Increasing Pe from 7000 to 30,000 yields non-linear performance gains, improving the actual heat transfer rate by 136.0% and efficiency by 27.6 percentage points. Furthermore, the counter-flow arrangement outperforms parallel-flow by 20.4% at Pe = 10,000, widening to 46.5% at Pe = 30,000, demonstrating that flow-arrangement thermodynamics fundamentally dominate channel-morphology complexity. Relative to conventional straight-channel baselines, the topology-optimized counter-flow design delivers a Thermal Enhancement Ratio of 1.58–2.22 at equal pressure drops. These findings establish quantitative design guidelines for topology-optimized dual-fluid heat exchangers in advanced thermal management applications.

To investigate the high pressure two phase discharge characteristics within the multi-stage pipelines of automatic depressurization system (ADS) under actual operating conditions, this study conducted experimental research on high pressure two phase discharge in multi-stage pipelines. The results shows that with an increase the number of depressurization stages, the pressure drop percentage of the discharge main pipeline increases, and the pressure drop percentage of ADS valve package decreases. Additionally, the position of the maximum pressure drop percentage in the valve package migrates upstream with the increase of depressurization stages. When the equilibrium quality is 90 similar to 100 % and the pressure is 2-13.6 MPa, the equilibrium quality along the flow direction initially decreases and then increases, and as the inlet pressure increases, the inflection point gradually moves downstream. In the other conditions, the equilibrium quality shows an upward trend. When the equilibrium quality is 10-90 %, the pressure is 0-13.6 MPa and the equilibrium quality is 0-10 %, the pressure is 2-13.6 MPa, the equilibrium quality changes significantly along the pipeline. And other conditions is not obvious.

Due to the similarity between the physical properties of seawater and freshwater, most scholars believe that the condensation oscillation characteristics of steam-seawater low-velocity jet are the same as those of steam-freshwater low-velocity jet, which leads to a lack of accurate understanding of the oscillation characteristics of steam-seawater jet. To explore the oscillation characteristics of steam-seawater low-velocity jet, a high-speed cameraand two high-frequency dynamic pressure sensorswere carried out to carry out a comparative study experiment between the steam-seawater low-velocity jet and the steam-freshwater low-velocity jet. Through experimental comparative analysis, it is found that the steam-seawater low-velocity jet and the steam-freshwater low-velocity jet have both similarities and obvious differences in phase interface structure, pressure oscillation intensity, pressure oscillation amplitude, and pressure oscillation spectrum. In particular, the amplitude of pressure oscillations in the pool is much smaller for steam-seawater low-velocity jet than for steam-freshwater low-velocity jet at higher water temperatures. The results of this study are helpful for understanding and mastering the condensation oscillation characteristics of steam-seawater low-velocity jet.

Modern advanced pressurized water reactors universally employ passive containment cooling systems (PCS) to maintain containment integrity under accident conditions. Due to spatial layout constraints, the passive containment cooling system (PCS) often features longer horizontal sections and shorter vertical sections, which weakens or even suppresses natural circulation, leading to flow instability and impairing the continuous heat removal from the containment. To investigate the operational characteristics of PCS with long horizontal sections, this study constructed an PCS experiment bench and employed a system analysis program to simulate system's performance under varying heating conditions. A comparison with experimental results demonstrated that the system analysis program can effectively calculate the operational behavior of a PCS with extended horizontal sections. Furthermore, the flow characteristics of the PCS under different operating conditions were computed, and the flow instabilities across these conditions were summarized and analyzed. Under low-load conditions, flashing was identified as the cause of flow instability. Under high-load conditions, flow instability was sequentially triggered by flashing in the riser section and boiling within the heat exchanger. Additionally, flow reversal was observed during the boiling-induced flow instability phase, and it was determined that pressure fluctuations in the heat exchanger caused by boiling are responsible for flow reversal in the downcomer section. The impact of the riser pipe structure on the PCS operational characteristics was studied, revealing that the length of the horizontal pipe influences the peak value of flow oscillations.

In the practical application of engineering, the phenomenon of steam underwater immersion jet under high back pressure conditions (>0.1 MPa) exists. However, most of the current research on steam immersion jet condensation flow patterns and their boundaries is conducted under atmospheric pressure conditions (0.1 MPa). The applicability of condensation flow patterns and related prediction formulas derived under atmospheric pressure to high back pressure conditions remains to be validated. Based on the experimental research, the condensation pattern of steam underwater immersion jet under different back pressure conditions is identified, and the condensation behavior of the jet under different back pressure conditions is clarified by comparing and analyzing the visual images and dynamic pressure characteristics of different condensation flow patterns, and the influence law of back pressure and other parameters on the condensation flow pattern boundary is mastered. This study fills the gap in the research of steam underwater immersion jet under the condition of high back pressure, which has important scientific research significance and engineering application value.

Currently, the design of the cold chain system for the HPR1000 nuclear island does not take a unified approach and largely relies on the design experience of the respective designers. The various subsystems contain numerous devices, and the cumulative design margins often result in many unreasonable parameters in the original design scheme of the cold chain system. To address this issue, this paper establishes a mathematical model for the cold chain system to assist in its design. Based on genetic algorithms and the simplex algorithm, adaptive relaxation constraint dominance relations and two improved NSGA-II multi-objective handling methods are introduced, leading to the development of a new hybrid multi-objective genetic algorithm. The performance of this algorithm is verified using optimized benchmark testing functions, thus allowing for the scientific optimization of the cold chain system design scheme. A sensitivity analysis is conducted on the design parameters of the ventilation system, refrigeration system, component cooling system, and seawater system within the cold chain system to explore the impact of these parameters on performance indicators. Optimization design calculations for the cold chain system are performed under safe and feasible conditions, resulting in an optimization scheme. The results indicate that the developed algorithm is effective in addressing the complex optimization problems of the cold chain system, and the optimized cold chain system can reduce weight by up to 18.4 %, volume by up to 18.6 %, investment costs by up to 5.7%, and system energy consumption by up to 7.5 %.

The passive containment heat removal system (PCS) is one of the key passive safety systems of China’s third-generation advanced pressurized water reactor—Hua-long Pressurized Reactor (HPR1000), used to prevent overpressure of large concrete containment under severe accident scenarios. This paper provides an overview of the development of the HPR1000 passive containment heat removal system, including its operating principles and configuration, internal heat exchanger design, feasibility tests, engineering-scale PCS verification tests, comprehensive tests on PCS–containment coupling characteristics, among other key supporting studies. These extensive studies demonstrated that the PCS of HPR1000, which is designed based on flashing-driven open natural circulation and efficient condensation heat transfer theory, can work effectively and ensure the integrity of the containment under various accident scenarios. The system has been applied to Fuqing No. 5 and No. 6 nuclear power units and Zhangzhou No. 1 and No. 2 units of China’s first million-kilowatt third-generation nuclear power HPR1000. It is also applied to K-2/K-3 units of Karachi Nuclear Power Plant in Pakistan.

To address the contradiction between safety and economy in double-layer concrete containment systems for nuclear power plants, this study focuses on China's third-generation nuclear technology. Based on the HPR1000 reactor design, a suppression containment system was previously proposed, and its response characteristics under typical accidents scenario were analyzed. However, parametric studies on factors influencing the heat removal capacity of the short-term heat release and pressure relief system (SHRPRS) were not conducted. Therefore, this paper investigates the effects of key parameters-including the gas space volume of the Multi-Functional Pool (MFP), cross-sectional area of the depressurization discharge pipes, and pipeline submersion depth-on the system's ability to suppress pressure and store non-condensable gases. Furthermore, configuration schemes for SHRPRS under different containment volumes to address Beyond-Design-Basis Accidents (BDBAs) are explored. Results indicate that for units without SHRPRS, containment volumes of 86,000 m3 and 70,000 m3 meet BDBA mitigation standards, while volumes of 60,000 m3 and 49,000 m3 fail to comply. For units equipped with SHRPRS, appropriate configurations of gas space volume and pipeline cross-sectional area enable all four containment volumes (86,000 m3, 70,000 m3, 60,000 m3, and 49,000 m3) to handle BDBA.

There is a significant gap between the component cooling system (CCS) of the HPR1000 nuclear island cold chain system and the actual operating parameters, resulting in insufficient utilization of the cooling source and poor economic performance. Due to the high complexity of CCS design and the difficulty of design evaluation, multiobjective optimization research is necessary to identify parameters that significantly impact the design results of the CCS. To this end, this paper constructs a mathematical model and evaluation program for the CCS, utilizing an improved genetic algorithm suitable for solving constrained complex multi-objective optimization problems. The design temperature of the CCS and several large design flow rates are selected as optimization variables, while weight, volume, investment cost, and energy consumption are set as optimization objectives. The aim is to use optimization design methods to determine the impact of important parameters of the CCS on its design. The results indicate that, under the premise of ensuring the safety of nuclear power plants, the optimization algorithm can effectively identify the optimal combinations of optimization variables, leading to relative optimal solutions for the four objectives: a maximum reduction of 18.1 % in weight, 21.3 % in volume, 11.5 % in investment cost, and 28.7 % in energy consumption. Furthermore, the study finds that the design temperature of the CCS is a crucial parameter affecting its design results, and that appropriately reducing the design temperature is a key direction for optimizing the CCS design.