Nuclear Pump Research Articles

The Influence and Optimization of Geometrical Parameters on Coast-Down Characteristics of Nuclear Reactor Coolant Pumps

Coast-down characteristics are the crucial safety evaluation factors of nuclear reactor coolant pumps. The energy stored at the highest moment of inertia of the reactor coolant pump unit is utilized to maintain a normal coolant supply to the core of the cooling loop system for a short period of time during the coast-down transition. As a result of the high inertia moment of the rotor system, the unit requires a high reliability of the nuclear reactor coolant pump and consumes considerable energy in the start-up and normal operation. This paper considers the operational characteristics of the coast-down transition process based on the existing hydraulic model of the nuclear reactor coolant pump. With the implementation of an orthogonal test, the hydraulic performance of the nuclear reactor coolant pump was optimized, and the optimal combination of impeller geometrical parameters was selected using multivariate linear regression to prolong the coast-down time of the reactor coolant pump and to avoid serious nuclear accidents.

Equivalent circuit method for circulating current loss of transposed strands in multi‐turn coil of a canned induction motor

For the particularity of the transposition method in large induction motor, the equivalent circuit method for the circulating current losses of the transposed strands in stator winding with multi-turn coil is put forward. According to the unified theory of the electromagnetic field-circuit and combining with the distribution of various leakage magnetic fields of stator winding, the general circuit network model of the stator winding is proposed, which can be applicable to different transposition angles with the consideration of the accurate distribution of leakage magnetic fields. With the basic idea of discrete points and the linearisation, the method for the leakage reactance of the transposed strands is given with an application in a 5.5 MW nuclear power pump canned induction motor, which uses the strand slot leakage reactance and the end leakage reactance to simulate the slot leakage magnetic field and the end leakage magnetic field. Through experiment, the equivalent circuit method for the circulating current losses of the transposed strands in multi-turn coil is verified, which will provide a reference for the winding design and the winding loss calculation of the large induction motor.

Study on shaft-block under small break loss of coolant accident of nuclear main pump

To make sure that the reactor could be well protected under various accidents, hypotheses shall be made in design of the reactor to address possible accidents. Currently, the studies on shaft-block under small break loss of coolant accident (SBLOCA) are insufficient. This paper could provide more reference to this field. Firstly, external characteristics before and after the shaft-block accident under SBLOCA are obtained through experiments. Then, computational fluid dynamics (CFD) analysis is used to analyze the change of inner flow and the interaction between SBLOCA and shaft-block accident of the nuclear main pump. This paper shows that after the shaft-block accident happens, the speed of the main pump is reduced to zero quickly, while the disappearance of the flow takes a longer time. While the impellers are slowing down, different parts in the blades lose the ability to transfer energy to the fluid one after another, which in external characteristic is demonstrated with the head and torque reducing to negative values successively. Relatively significant change in the inner flow field of the pump happened in the shaft-block process, and clear regular change pattern could be found in rotor and stator blade interaction. The impact of SBLOCA on the shaft-block accident of the nuclear main pump is mainly on the external characteristic changes in the early stage of the accident, and the higher the extent of SBLOCA is, the more significant the impact will be.

Study on the influence of cavitation development on the performance of nuclear main pump

In order to study the influence of cavitation on the external characteristics and inner flow field of nuclear main pump, based on the continuity equation, Reynolds N-S equation and RNG k-ε turbulence model, the whole flow field cavitation numerical simulation on nuclear main pump model under the design condition is carried out. The performance and internal flow field variation law of the nuclear main pump are obtained through the comparison and analysis when 4 kinds of cavitation conditions are chosen. The results show that the head, efficiency and power of the nuclear main pump have different sensitivities to the reduction of net positive suction head available (NPSHa). With the development of the cavitation process in the pump, the head declines most sharply and the power most moderately. Under the condition of cavitation, the bubbles generated by cavitation have a squeezing effect on the impeller passage, which makes the flow area decrease and the relative velocity of the fluid increase. Meanwhile, the value of maximum velocity appears near the outlet of the blade. Meanwhile, the bubbles generated by cavitation change the flow state of the cavitation region, which makes the kinetic viscosity of fluids, the turbulent dissipation rate and the loss of turbulent dissipation reduce.

Research on the force of radial bearing of a nuclear main pump rotor system by database method

This paper discusses the method of solving the radial sliding bearing force of a nuclear main pump rotor system using the pre-built database. For a sliding bearing with a certain size, the Reynolds equation can be decomposed and be equivalent of the problem of solving the liquid film pressure in both pure rotation and pure extrusion states. A database for solving the bearing force is established by pre-calculating the liquid film pressure of the radial sliding bearing under these two states with different eccentricities. By comparing with three analytical models, the bearing forces obtained by this method are closer to the results obtained by the finite difference method. And compared with the finite difference method, the method is much faster.

Robot automation grinding process for nuclear reactor coolant pump based on reverse engineering

The nuclear reactor coolant pump (NRCP) is the heart of the nuclear power plant. This paper focuses on robot automation grinding processing for NRCP, which includes scanning, point cloud processing, grinding trajectory generation, and quality evaluation system based on reverse engineering. In this work, firstly, the point cloud of NRCP is obtained by robotic scanner system of hand-eye calibration. Secondly, the research proposes a novel method for point cloud simplification, denoising, and boundary extraction base on k neighborhood octree structure. More important, the efficient trajectory generation of grinding relies on transforming point cloud into adaptive triangular mesh. Lastly, quality evaluation system can calculate the deviation between point cloud and qualified workpiece. And the further path is generated according to the deviation. Experiments show that the accuracy of “246” hand-eye calibration method is less than 0.02 mm. The method of point cloud processing has obvious efficiency advantages over other researchers’ algorithms. The final results indicate that the error of grinding is less than 3 mm and efficiency can be improved by 2.5 times compared with manual grinding.

Study on grinding damage of high chromium alloy based on molecular dynamics

The new cast high chromium alloy is the conventional material of the nuclear main pump thrust-bearing with good wear and corrosion resistance. According to the structural characteristics of high chromium alloy, the simulation model and the coupling potential function were constructed to study the grinding damage layer using molecular dynamics method. The simulation results show that the crystal lattice distortion caused by carbon atoms in the formation of interstitial solid solution leads to the occurrence of amorphous structure after full relaxation. The break and recombination of metal bond and non-metal bond between atoms in the alloy result in the occurrence of damaged layer under grinding. And the bond angles between the atoms in the damage layer are less than that in the alloy matrix. The damage layer is mainly composed of atoms in front of the abrasive particle and the atoms of extrusion deformation in the bottom. Moreover, with the increase of grinding depth, the cutting force and the damage layer thickness increase. The study is conducive to understand the damage formation mechanism of high-chromium alloy materials in micro-nano processing, and provides a theoretical reference value for the actual processing.

Optimal design of the guide vane blade of the CAP1400 coolant pump based on the derived multi-source constrained zone

Abstract The vane takes over the role of guiding the high-speed flow and decreasing the unbalance radial forces from the rotating impeller, which is important for the safety and long-term serving of the coolant pump. To design the vane blade effectively, a new constrained zone generating the satisfied and efficient design variables was deduced out from the summarized multi-source constrained conditions. Based on the derived constrained zone, an optimization system comprised of the Computational Fluid Dynamics (CFD) analysis, the Latin Hypercube Sampling (LHS) method, the approximate model, and the Multi-Objective Particle Swarm Optimization (MOPSO) was established. Taking the 1:2.5 scaled 1400-MW canned nuclear coolant pump as the target, the optimal sample was gotten successfully, and the following conclusions could be concluded as: the influence degrees of the design variables were ranked with RSM analysis; the optimal sample’s efficiency was 2.2% higher than the target, and its head was about 3% greater; the unsteady analysis denoted that the optimal result could decrease the pressure fluctuation and the radial forces effectively, which means that it does good for the safety and long-term serving of the coolant pump. The study is expected to provide a technical reference for the third-generation nuclear power plant design.

Application of the Modified Inverse Design Method in the Optimization of the Runner Blade of a Mixed-Flow Pump

To improve the design speed and reduce the design cost for the previous blade design method, a modified inverse design method is presented. In the new method, after a series of physical and mathematical simplifications, a sail-like constrained area is proposed, which can be used to configure different runner blade shapes. Then, the new method is applied to redesign and optimize the runner blade of the scale core component of the 1400-MW canned nuclear coolant pump in an established multi-optimization system compromising the Computational Fluid Dynamics (CFD) analysis, the Response Surface Methodology (RSM) and the Non-dominated Sorting Genetic Algorithm-II (NSGA-II). After the execution of the optimization procedure, three optimal samples were ultimately obtained. Then, through comparative analysis using the target runner blade, it was found that the maximum efficiency improvement reached 1.6%, while the head improvement was about 10%. Overall, a promising runner blade inverse design method which will benefit the hydraulic design of the mixed-flow pump has been proposed.

Cavitation erosion behavior of Hastelloy™ C-276 weld by laser welding

Ni-based Hastelloy C-276 was chosen as the material of the stator and rotor cans of a nuclear main pump for its excellent resistance to corrosive environments and superior mechanical properties. In the present work, the cavitation erosion (CE) behavior of the Hastelloy C-276 thin sheet weld joint was tested. The results indicate that both the CE damages of the weld metal and the base metal initiate at grain boundaries preferentially. The solidification grain boundaries (SGBs) of the weld metal and the twin boundaries (TBs) of the base metal are more susceptible to CE. For the weld metal, due to the microstructure inhomogeneity, regions that show the highest damage intensity are located near the central line of the weld surface where the columnar dendrites interact with the nearly equiaxed dendrites. For the base metal, grains with more TBs are damaged faster compare to other grains. The surface roughness of the eroded surfaces increases with exposure time, and the surface roughness of the base metal increases faster than that of the weld metal. Overall, the resistance to CE of the weld metal is better than that of the base metal.

Preparation and Experimental Study of Graphite Material for Water Lubricated Thrust Bearing of Nuclear Main Pump

Based on technical difficulties of graphite water-lubricated thrust bearing such as preparation and properties detection, this paper investigated graphite bearing systematically from preparation and property testing, three different types of graphite (#1, #2 and #3) were carried out. The result indicated the tribological properties are poor if the graphitization of graphite is too high or low. The pads of water-lubricated thrust bearing are manufactured by the three kinds of graphite, and the start-stop test were carried out on a test platform for half-size bearing of nuclear primary pump. The result of start-stop test were indicated the graphitization have a visible influence on the wear loss mass of graphite pad.

Theoretical Solutions for Dynamic Characteristics of Liquid Annular Seals with Herringbone Grooves on the Stator Based on Bulk-Flow Theory

Liquid annular seals are primarily used to control the leakage in high-speed turbomachinery, especially in nuclear and petrochemical pumps. In this paper, a theoretical analysis method for dynamic characteristics of liquid seals with herringbone grooves on the stator is proposed based on bulk-flow theory. Steady-state velocities and leakage rates within the upstream and downstream spiral parts and the middle plain part taking account of the pumping effects are figured out first with the inertia term of the fluid within the whole seal. Then, the dynamic characteristics of the whole seal are solved based on Childs’ finite-length solutions and verified by comparing with experimental hydraulic forces. Moreover, characteristic coefficients and instability parameters of the herringbone-grooved teeth-on-stator (TOS) seals and teeth-on-rotor (TOR) seals of the same size under different pressure differences are predicted and compared in detail. The influences of the lengths of constituent parts on the dynamic characteristics and instability parameters of the model seals are theoretically investigated. The results show that the stability of the TOS seal is much better than that of the TOR seal under most operating conditions. And the lengths of the middle plain part significantly affect the dynamic characteristics and the stability parameter.

Experimental and numerical investigation on the pressure pulsation and instantaneous flow structure in a nuclear reactor coolant pump

Abstract The instantaneous vortical flow structure is one of the typical flow structures inside the nuclear reactor coolant pump (RCP), which would cause the unsteady pressure pulsations, vibrations of the unit and fatigue of components. Due to high safety requirement of the RCP during the actual operation of the nuclear power plants (NPPs), revealing instantaneous nature of vortical flow structure and its pressure pulsation becomes a crucial issue for studying the internal flow mechanism of the RCP. The purpose of this study is to shed comprehensive light on the pressure pulsation and instantaneous vortical flow structure in the RCP by using the experimental method and the numerical simulation method. Based on the result of comparison with the experiment and numerical simulation, it can be considered that the LES method can better identify instantaneous nature of vortical flow structures in the low frequency band. The instantaneous vortical flow structure is attached to the impeller RBPS (rotor blade pressure surface) and transient jet wake vortex flow structures between the impeller and diffuser under the rotor-stator interaction effect are fairly obvious by Q-criterion. On the other hand, in the axial-vorticity component distribution, the rotor-stator interaction effect between the impeller and diffuser cannot be clearly revealed. From the three-dimensional structures, the main vortex structures are in the front and back cavity of the right-hand side near the discharge nozzle and the right-hand side below the discharge nozzle in the spherical casing. Meanwhile, combined with pressure spectrum, it is convinced that their unsteady characteristic is the main reason that causes complex excitation frequencies in the low frequency band of the right-hand side near the discharge nozzle.

ETV7-Mediated DNAJC15 Repression Leads to Doxorubicin Resistance in Breast Cancer Cells

Breast cancer treatment often includes Doxorubicin as adjuvant as well as neoadjuvant chemotherapy. Despite its cytotoxicity, cells can develop drug resistance to Doxorubicin. Uncovering pathways and mechanisms involved in drug resistance is an urgent and critical aim for breast cancer research oriented to improve treatment efficacy. Here we show that Doxorubicin and other chemotherapeutic drugs induce the expression of ETV7, a transcriptional repressor member of ETS family of transcription factors. The ETV7 expression led to DNAJC15 down-regulation, a co-chaperone protein whose low expression was previously associated with drug resistance in breast and ovarian cancer. There was a corresponding reduction in Doxorubicin sensitivity of MCF7 and MDA-MB-231 breast cancer cells. We identified the binding site for ETV7 within DNAJC15 promoter and we also found that DNA methylation may be a factor in ETV7-mediated DNAJC15 transcriptional repression. These findings of an inverse correlation between ETV7 and DNAJC15 expression in MCF7 cells in terms of Doxorubicin resistance, correlated well with treatment responses of breast cancer patients with recurrent disease, based on our analyses of reported genome-wide expression arrays. Moreover, we demonstrated that ETV7-mediated Doxorubicin-resistance involves increased Doxorubicin efflux via nuclear pumps, which could be rescued in part by DNAJC15 up-regulation. With this study, we propose a novel role for ETV7 in breast cancer, and we identify DNAJC15 as a new target gene responsible for ETV7-mediated Doxorubicin-resistance. A better understanding of the opposing impacts of Doxorubicin could improve the design of combinatorial adjuvant regimens with the aim of avoiding resistance and relapse.

Safety integrity level evaluation of nuclear centrifugal pump based on performance degradation data

To reduce personnel and equipment risks related to centrifugal pumps in nuclear power plants, safety integrity level for centrifugal pumps must be evaluated. The safety integrity level evaluation m...

Simulation of a hydraulically controllable reactor coolant pump seal

Abstract A hydraulically controllable mechanical seal for a nuclear reactor coolant pump (RCP) is under development. Its purpose is to correct excessive or insufficient leakage through RCP seals, a current expensive problem. The non-rotating seal face contains an annular cavity, filled with pressurized fluid. By changing the pressure within the cavity, the deformation and geometry of the face can be changed. Since the face geometry determines the thickness of the lubricating film between the two seal faces and the leakage rate, the leakage rate can be controlled. Simulations indicate that the hydraulically controllable seal provides sufficient control to address many abnormal leakage rate scenarios.

Optimization of the cross section area on the meridian surface of the 1400-MW canned nuclear coolant pump based on a new medial axial transform design method

Canned coolant pump is the only rotating part of the nuclear island, which provides continuous power for the medium circulation. Therefore, new innovative approaches to improve the pump’s performances are of great significance. To adjust the hub and shroud profiles spontaneously and control the scale of the design parameters effectively, a special investigation about optimizing the distribution of the cross section area on the meridian surface would be done here. In order to represent the meridian shape accurately with the corresponding expected cross section area distribution, the new design strategy established on the Media Axis Transform (MAT) design theory was presented firstly. Then with the integration of the new meridian design approach, Computational Fluid Dynamic (CFD) analysis, Central Composite Design (CCD), Respond Surface Method (RSM) and Non-nominated Sorting Genetic Algorithm-II (NSGA-II), an optimization system was ultimately established. Taking the scale model of CAP1400 (on a scale of 1:2.5) as the reference, the optimal cross section area distribution was gotten successfully after the optimization. Ultimately, the optimal distribution of the cross section area was obtained, and through CFD analysis and inner flow analysis, it can be found that the performances of the optimal sample are improved in relative to the reference model from 0.8Qd to 1.2Qd. Most importantly, at the design point, the increasement of efficiency is 1.7%, while the head improvement is about 2.6%. The study here is expected to provide a new strategy for the meridian surface optimization of the large-scale turbomachinery with front and rear matching parts.

Research on the non-uniform inflow characteristics of the canned nuclear coolant pump

Computational fluid dynamics is used to analyze the velocity field of the inflow and the pressure loading on the blades of the reactor coolant pumps under different conditions. The Reynolds-averaged Navier-Stokes equations with the k-ε turbulence model were solved to simulate both steady and unsteady states of the inflows. The model was validated with experiments on the heads and efficiencies by testing a straight pipe at different flow rates. With this model, the paper demonstrates that, by replacing the straight pipe with a channel head, the inlet flow field of the impeller becomes non-uniform, forming a swirling flow under lateral pressure differences and a local low-energy region near the tube wall. The inlet distortion destroys the circular symmetry of the flow field and reduces the head and efficiency of the pump. The flow field in the impeller is more complicated and chaotic and imposes an unbalanced force on the impeller thus increasing the risk of fatigue failure of the impeller. Because of the significant effect of the non-uniform inflow induced by the channel head on the performance of the pump, understanding the underlying mechanism is of importance in improving the design of the reactor coolant pump.

Hilbert spectrum analysis of unsteady characteristics in centrifugal pump operation under cavitation status

Cavitation has negative influence on nuclear pump operation. In order to detect incipient cavitation effectively, experimental investigation was conducted for acquisition of current and vibration signals during cavitation process. In this research, a centrifugal pump was modeled for nuclear pump research. The data was analyzed by HHT method. The results show that Torque oscillation resulted from unsteady flow during cavitation process could result in energy variation. RMS of IMF in current signal is sensitive to cavitation occurrence. It could be regarded as the indicator of incipient cavitation. RMS variation of IMF in radial vibration signals experiences monotone increasing tendency when cavitation gets severe. Such variation regulation could be selected as the indicator of cavitation stage recognition. Hilbert-Huang transform is suitable for transient and non-stationary signal process. Time-frequency characteristics could be extracted from results of HHT process to reveal pump operation condition. The contents of current work could provide valuable references for further research on centrifugal pump operation detection.

Investigations of the unstable Q-H hump characteristic of a nuclear main pump

As an important component of the nuclear power plant, nuclear main pump has high requirement in terms of the operational stability. An important stability problem of the nuclear main pump unit is t...