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Under the influence of marine conditions on nuclear powered ships, the liquid storage in the Pressurizer shake violently, which affects the normal operation of the Pressurizer and even causes safety accidents. Therefore, it is extremely urgent to design an anti-wave device for the Pressurizer. This paper studies a Pressurizer model with a ring-shaped plate. Using numerical simulation software, the VOF method is used to couple the k-ε model to simulate the liquid level fluctuation of the two Pressurizers with and without anti-wave device under different external excitation cycles. The phenomenon of internal liquid level fluctuation during movement was analyzed, and the pressure transient change characteristics of the pressure monitoring points arranged on the pressurizer were analyzed, so as to compare the different axial sections and the overall water level shaking amplitude. By comparing the simulation results, it is found that when the external excitation period is T = 2∼2.5s, the ring-shaped plate studied in this study can suppress the shaking of the liquid storage in the Pressurizer significantly.

Liquid sloshing will occur in liquid storage tanks such as accumulator of floating nuclear power plant (FNPP) subjected to additional inertial forces under motion conditions. The study carried out measurement experiments based on the 6-DOF platform to study the sloshing characteristics and pressure variation rule of the accumulator. The results show that surging will induce many kinds of nonlinear free surface sloshing forms, it can be seen that the law of pressure variation is mainly dominated by natural frequency and excitation frequency based on time and frequency domain analysis. Then the study combines the automatic encoder and extreme learning machine to build the deep extreme learning machine (DELM) network to predict the pressure in time series. Based on the phase space reconstruction of the time sequence, the pressure results of the next time are output after the last 15 pressure data are input. The prediction results show that the DELM model has fast speed and high precision and the predicted value is in good agreement with the experimental data. So this study can provide a reference for the pressure monitoring and the artificial intelligence application of FNPP.

The pressurizer of floating reactor moves dramatically with the of ocean waves, and liquid in pressurizer will slosh when subjected to additional inertial force. To study the hydro characteristics of the liquid in pressurizer, this paper analyzed the flow field and pressure variation of pressurizer under typical moving conditions. Combined with the influence factors of typical motion on the transient pressure variation characteristics at monitoring position under different working conditions, optimize the differential pressure measuring method of liquid level through numerical simulation, result in reduce the liquid level measuring deviation. Traditional numerical approach of liquid sloshing is improved based on the modified motion equation and coordinate transformation matrix approach. Combined with the moving grid and modified algorithm. Through comparison. The results show that the liquid level measuring deviation of heave motion with vertical additional acceleration and the pressure variation of rolling motion is mainly caused by the spatial position variation of the model and the liquid free surface. The mechanism of coupling of heave motion and rolling motion can be comprehensively considered in combination with the influences of every individual motion. In addition, through verification, the liquid level measuring can be corrected according to the attitude data and geometric information of pressurizer.

The study of the effect of blockage on two-phase flow parameters in rod bundle is of significance to the prediction of the thermal-hydraulic behavior of fuel assembly under hypothetical accident conditions. The two-phase flow computational fluid dynamics method was used to simulate the fluid flow phenomenon in 5 × 5 under no- and total sub-channel blockage conditions. The effect of the blockage on the void fraction is most significant in the sub-channel where it is located and the adjacent sub-channels. The effect of the blockage on other flow parameters extends as far as 46 Dh downstream of the blockage. There is an increase in the void fraction after the blockage as a result of bubble coalescence in the region. The effect of these different blockage conditions can provide a reference for the parameter setting of the sub-channel analysis codes.

In case of core emergency cooling safety injection, the boron containing coolant injected externally and dilution water mass will be mixed in the pressure vessel. The uneven mixing of boron containing coolant and dilution water mass may lead to the return of the core to criticality. Therefore, it is of great significance to accurately measure the boron concentration distribution in the pressure vessel and study the mechanism affecting the mixing process for the safe operation of the reactor. In this paper, combined with the structural characteristics of HPR1000 pressure vessel, a visual experimental device is built through proportional modeling design, and the flow mixing process of diluted water mass, safety injection solution and coolant in the pressure vessel under double loop operation is obtained by using plane laser-induced fluorescence technology, the effects of different Reynolds numbers on the diffusion of boric acid were experimentally studied. The experimental results show that under the condition of double loop, the two inlets divide the circumferential direction into good arc and bad arc. The velocity distribution of fluid flowing through the bad arc is more uniform, while the vertical flow of fluid flowing through the good arc is uneven; The fluid flows downward rapidly after the intersection on the inferior arc side, and the intersection height is positively correlated with the cold pipe flow, while the fluid on both sides shows obvious mixing after the intersection on the superior arc side; Clear water mass cannot be avoided at the core inlet, but increasing the cold pipe flow and safety injection flow can reduce the time of clear water mass flowing through the core.

Thermal-hydraulic behaviors within a PWR fuel assembly is very complex under accident conditions and marine conditions, which has a significant impact on reactor safety. It is crucial to carry out studies on thermal-hydraulic properties under transient conditions. A telecentric lens and a pulse signal generator are applied to improve the performance of PIV system, a high temporal and spatial resolution measurement for flow fields in rod bundle channels is achieved, the velocity distribution in rod bundles are obtained under accelerating flows and decelerating flows. The steady-state flow field is measured to use as a reference, the effect of flow fluctuations on the flow fields in the rod bundle is analyzed. The results present, the accelerating flows improve the velocity gradient between adjacent flow layers in rod bundles and weaken the lateral velocity. In the contrary, the decelerating flows weaken the velocity gradient between flow layers in rod bundles and improve lateral velocity. Conversely, the velocity gradient attenuates in decelerating flows between the rod beam layers and increases the lateral velocity. During the accident, the thermal-hydraulic behavior in the reactor has the characteristics of transient complexity and uncertainty. Studying the flow and heat transfer characteristics of the reactor core fuel assembly under accident conditions can improve a understanding for the accident development process.

We experimentally, numerically and theoretically investigate the nonlinear interaction between a cavitation bubble and the interface of two immiscible fluids (oil and water) on multiple time scales. The underwater electric discharge method is utilized to generate a cavitation bubble near or at the interface. Both the bubble dynamics on a short time scale and the interface evolution on a much longer time scale are recorded via high-speed photography. Two mechanisms are found to contribute to the fluid mixing in our system. First, when a bubble is initiated in the oil phase or at the interface, an inertia-dominated high-speed liquid jet generated from the collapsing bubble penetrates the water–oil interface, and consequently transports fine oil droplets into the water. The critical standoff parameter for jet penetration is found to be highly dependent on the density ratio of the two fluids. Furthermore, the pinch-off of an interface jet produced long after the bubble dynamics stage is reckoned as the second mechanism, carrying water droplets into the oil bulk. The dependence of the bubble jetting behaviours and interface jet dynamics on the governing parameters is systematically studied via experiments and boundary integral simulations. Particularly, we quantitatively demonstrate the respective roles of surface tension and viscosity in interface jet dynamics. As for a bubble initiated at the interface, an extended Rayleigh–Plesset model is proposed that well predicts the asymmetric dynamics of the bubble, which accounts for a faster contraction of the bubble top and a downward liquid jet.

Ocean conditions will cause ships to be affected by rolling, heaving and other motions, which introduce additional inertial forces to the marine nuclear power system, introduce additional pressure drop to the fluids in each loop, bring errors to the measurement of thermal hydraulic parameters such as pressure difference and flow rate. Therefore, the measurement of pressure difference and flow rate under ocean conditions is studied and corrected in this paper. We built a rolling platform and a heaving platform and measured the differential pressure and flow rate under various working conditions. Through analysis, the relationship between differential pressure, flow fluctuation and swaying, undulating and other movements under moving conditions was obtained. Besides, the calculation method of attached pressure drop was analyzed, and the following conclusions were obtained: The influence of motion on differential pressure and flow rate is mainly composed of two parts: The additional pressure drop caused by the swinging motion of working medium in the pipeline and the pressure lead-in pipe, and the periodic fluctuation of friction pressure drop caused by the periodic fluctuation of flow velocity caused by swinging motion. The attached pressure drop caused by motion can be calculated through theoretical analysis. Through the analysis of experimental data and the comparison of theoretical calculation methods, it is found that the pressure drop measured by the experiment is in good agreement with that fitted by the theoretical calculation, and the modification scheme of pressure difference under ocean conditions is feasible to some extent.

As human beings explore the outer space, the demand for the nuclear sources in space missions is increasing. Almost all the existing space nuclear reactors have adopted the design of gas-cooled fast reactor, and the temperature feedback effect of the fuel of the small fast neutron reactor is different from that of the traditional pressurized water reactor. For the space fast reactors, they are designed to be compact and with a long operating lifetime to accomplish the long-term space missions. Due to the high-level enrichment of U-235 in the fuel, the Doppler effect of U-238 has little impact on the reactor reactivity. In the present paper, based on the design of the megawatt-class space gas-cooled fast reactor, the overall temperature feedback adjustment capability of the core, and the overall temperature coefficient of the core including fuel, structural materials, and coolant are investigated. The calculation results show that the temperature of the coolant has little effect on the reactivity. The temperature coefficient of the fuel is positive, and the structural material with a large negative temperature feedback coefficient. At the same time, the deformation of the fuel pellets due to thermal stress at high temperatures and the reactivity changes caused by the deformation are analyzed.

The rod bundle fuel is characterized by compact structure and narrow flow passage. The fragments and corrosion products, flowing with the coolant, can cause local blockage accident, threaten the integrity of the fuel cladding. Therefore, it is necessary to use the Particle Image Velocimetry (PIV) to visualize and measure the flow fields downstream of the blockages. The results show that partial blockages will cause flow reversal. In the backflow zone, vortices are generated downstream of the blockage, causing increase in the resistance. The length of backflow zone increases with the increase of the Reynolds number. The wake area formed downstream of the blockage presented periodic changes with the time and the period is about 0.8s. For the blockage of the interior subchannels, in the backflow zone, two rows of asymmetrically distributed vortices, and the vortices interfere with each other and cause squeeze deformation. For the blockage of the side and corner sub-channels, the formed vortices have irregular shape and nonuniformed distribution, and the flow field is more complex and changeable. This is believed to be caused by the high intensity turbulence and the influence of the wall.

Bubbling deaeration is widely applied in marine steam power system (MSPS), and direct contact condensation (DCC) of steam injected into water under low subcooled water is the thermodynamic foundation of this technology. Due to the small delta-T below saturation of the flow field, the steam condensation potential is small, and there is a violent steam plume evolution. The process and the growth, merging, breaking and collapse of bubbles, which produce severe pressure oscillation and vibration noise. In response to this problem, the flow pattern evolution and acoustic characteristics of underwater steam injection in the range of different subcooling degrees (10–0.2°C) and steam mass flow (18kg/h) were studied through experiments. Studies have found that the degree of subcooling has an important impact on the evolution of the steam plume and the spectral characteristics of noise. The change in the shape of the steam plume determines the amplitude and spectral characteristics of the noise sound pressure. As the ambient water temperature rises, the steam plume shape changes differently, and the phenomena such as “tail oscillation”, “congestion”, and “steam recirculation” appear in sequence. Affected by the evolution of the above-mentioned steam plume shape, the noise sound pressure amplitude changes with the subcooling. The temperature first rises and then falls, and it rises slightly when it is close to the saturation temperature. At the same time, the noise spectrum shifts from medium and low frequency to low frequency. When it is close to the saturation temperature, the spectrum tends to move to medium frequency.

The floating reactor system will be rolling, heaving and other movements affected by waves, wind, etc. These motions will introduce additional inertial force field into the rod bundle, thus affecting the flow characteristics in the rod bundle channel. In order to study the influence of rolling motion on the flow characteristics of rod bundle, a visualization research of the flow field of rod bundle channel with a pitch-to-diameter ratio of 1.326 was carried out under rolling motion. The results show that under a small driving force, the rolling motion has a significant effect on the flow field in the rod bundle, affecting the velocity distribution in different sub-channels, and there is transverse mixing between adjacent sub-channels. With the increase of driving force, the influence of rolling motion is gradually weakened. The flow field distribution under rolling motion is significantly different from that under pulsating flow. The experimental results show that the influence of rolling motion on the middle sub-channel of the rod bundle channel is small, and the influence on the edge sub-channel is large. The velocity field of the subchannels on both sides of the edge fluctuates periodically, and the wave phase is inverse. This study shows that the flow field variation caused by rolling motion is different from that caused by pulsating flow, and the flow field of fuel assembly in floating reactor system under ocean condition is further studied.