Search Results (9)

This study investigates a shielded reactor coolant pump (RCP) using a thermo-fluid–structure interaction approach to numerically simulate the internal flow characteristics, impeller forces, and rotor vibration modes during rapid start-up following a loss of power accident under high-temperature and high-pressure conditions. A three-dimensional fluid–structure coupling model was established, employing the SST k-ω turbulence model and a one-way fluid–structure interaction method. The effects of three different start-up acceleration rates on pump head, pressure pulsation, vortex structures, turbulent kinetic energy distribution, and dynamic stress on the impeller were systematically analyzed. The results indicate that the medium-acceleration scenario (4.5 s start-up time) exhibits the most favorable performance in terms of pressure pulsation control, vorticity suppression, and stress distribution, effectively avoiding cavitation and structural resonance while ensuring a smooth and reliable start-up process. Modal analysis reveals that the rotor system is predominantly characterized by bending vibrations with satisfactory torsional stiffness and appropriately set critical speeds, presenting no resonance risks. This research provides theoretical foundations and engineering references for the safe restart of RCPs under extreme operational conditions. Full article

As the critical component of a nuclear power plant (NPP), the reactor coolant pump (RCP) will suffer energy losses during operation, which can lead to a series of safety issues and adversely affect the efficiency and stability of the NPP. In this study, the SST k-ω turbulence model is utilized to simulate the internal flow field of an axial-flow reactor coolant pump (RCP) under operating conditions of 0.8Q_N to 1.2Q_N. Combined with entropy production theory, the distribution characteristics and hydraulic causes of energy loss within different regions of the RCP are revealed. The research findings are as follows: the total entropy production in the RCP first decreases and then increases during operation; with turbulent entropy production consistently accounting for over 70% of the total, and direct entropy production accounting for less than 10%. The impeller and annular casing are always the main components responsible for hydraulic losses within the pump. As the flow rate increases, the total entropy production in the impeller initially decreases and then increases, accounting for between 34.3% and 51% of the total; with energy losses mainly concentrated on the suction side of the impeller blades. The total entropy production in the annular casing gradually increases under operating conditions ranging from 0.8Q_N to 1.2Q_N, accounting for between 20.4% and 50.3% of the total. Rotor-stator interaction (RSI), backflow, and flow separation near the volute tongue are significant causes of energy losses within the annular casing. Optimizing the geometric parameters of the impeller and annular casing is an effective way to reduce flow losses in axial-flow RCPs. The research results can provide a reference for the development of optimization techniques for RCPs. Full article

The reactor coolant pump (RCP) is the only rotating equipment in the primary circuit system of a nuclear power plant and the “heart” of the nuclear reactor. The L formula is defined, and the L/h_imp is introduced to study the influence of impeller blade type on the performance of the RCP. Twenty groups of models are designed, the concept of arc height ratio is proposed from the perspective of h_imp and L, and the distribution of internal entropy production within the impeller of the RCP under different Ls and h_imps of the impeller blade type is analyzed. The results show that when himp remains un-changed and L increases, the low-pressure area at the inlet of the impeller expands while the high-pressure area at the outlet decreases under the design flow or large flow conditions. The smoother blade profile reduces the occurrence of secondary flow phenomena and makes the RCP pressure distribution more uniform. Under design flow and large flow conditions, smaller L/h_imp and higher h_imp lead to higher efficiency and head performance. However, higher efficiency and lower head performance can be achieved under small flow conditions with larger L/h_imp and lower h_imp. Full article

In order to obtain the pressure pulsations of a reactor coolant pump during flow coast-down conditions, the time-domain characteristics of the flow passage under different times of flow coast-down were calculated by numerical calculation. Because the unsteady pressure pulsation signals in the RCP under flow coast-down are non-stationary and some phenomena may only occur in a short time, this paper analyzed them with the wavelet transform. The results show that the pressure fluctuation varies dramatically with the flow coast-down process and the variation rate of the pressure fluctuation coefficient can reach more than 60%. With the development of flow coast-down, there is a strong correlation between the pressure pulsation and number of impeller blades. The main frequency of the pressure pulsation gradually changes from high-frequency pulsation to low-frequency pulsation, and the regularity of the pressure pulsation is quickly destroyed, while the change in pressure pulsation regularity of the guide vane passage is more gentle than that of the impeller and pressurized water chamber. The change in wavelet intensity at the impeller outlet, guide vane inlet, and left side of the pressurized water chamber is more intense than at other areas. Full article

The annular seal between stator and rotor substantively acts as a bearing that affects the rotordynamic characteristic of the turbomachinery rotor system. The rotor wake turbulence in a canned motor Reactor Coolant Pump (RCP) will lead to inflow pressure distortion at the annular seal entrance, thus further affecting the seal rotordynamic characteristics and threatening the stable operation of RCP. In order to obtain the seal rotordynamic coefficients, a transient numerical method applies the mesh deformation technique to simulate the multiple-frequency elliptical rotor whirling orbit model. The transient solutions were proposed to solve the unsteady reaction forces of annular seals at five excitation frequencies for each case. The inflow pressure distortion patterns were simplified as harmonic functions, including two important influence parameters that are impeller blades number m and pressure fluctuation ratio $\lambda$. The numerical results showed that with nonuniform time-averaged pressure distribution at the entrance of the annular seal in Case 2, the inflow distortion significantly affects the seal rotordynamic coefficients, while the rotational spinning speed in Case 3 can weaken the time-averaged nonuniformity and accordingly make a dent in the influence. Increasing impeller blades number m and pressure fluctuation $\lambda$ both result in a sharp diminution of the negative stiffness $K_{eff}$, as well as an obvious increase in the effective damping $C_{eff}$, which will strengthen rotor misalignment and system stability. In addition, the larger impeller blades number m and higher pressure fluctuation $\lambda$ will make the effective damping $C_{eff}$ more independent of the whirling frequency. These results provide theoretical guidance for the operation safety of RCP. Full article

In order to study the effects of the suction and discharge conditions on the hydraulic performance and unsteady flow phenomena of an axial-flow reactor coolant pump (RCP), three RCP models with different suction and discharge configurations are analyzed by computational fluid dynamics (CFD) method. The CFD results are validated by experimental data. The hydraulic performance of the three RCP models shows little difference. However, the unsteady flow phenomena of RCP are significantly affected by the variation of suction and discharge conditions. Compared with that of Model E-S (baseline, elbow-single nozzle), the pressure pulsation in rotating frame of Model S-S (straight pipe-single nozzle) and Model E-D (elbow-double nozzles) is weakened in different degrees and forms, due to the more uniform flow fields upstream and downstream of the impeller, respectively. It indicates that the generalized rotor-stator interaction (RSI) actually exists between the rotating impeller and all stationary components causing the circumferentially non-uniform flow. Furthermore, improving the circumferential uniformity of the flow upstream and downstream of impeller (suction and discharge flow) also contributes to reducing the radial dynamic fluid force acting on the impeller. Compared with those of Model E-S, the dynamic F_X and F_Y of Model S-S are severely weakened, and those of Model E-D also gain a minor amplitude decrease at f_BPF. In contrast, the general pressure pulsation in fixed frame is mainly related to the rotating impeller and barely affected by the suction and discharge conditions. Full article

In order to study the influence of eccentricity on hydrodynamic characteristics of nuclear reactor coolant pump under different cavitation conditions, five different schemes were obtained by analyzing and optimizing the existing structural schemes. Based on the RNG k-ε model (Renormalization Group with k-epsilon turbulence models) and two-fluid two-phase flow model, the unsteady numerical analysis and test verification of different designed schemes are carried out by using the flow field software ANSYS CFX. The results of research show that different eccentricities will affect the nuclear reactor coolant pump’s head under different cavitation conditions, and the corresponding head in the scheme with the eccentricity of 5mm under the fracture cavitation condition is lower than that of the other schemes. When the impeller rotates at a certain angle from the initial position under critical and severe cavitation conditions, the radial force acting on the rotor system will fluctuate greatly. Under the condition of fracture cavitation, the radial force changed periodically and the resultant force value is small. Compared to the original scheme, the peak value of radial force is 6° clockwise after eccentricity of the impeller appeared. With the aggravation of cavitation condition, the axial force value of impeller decreases, but the corresponding amplitude of the impeller increases. Under critical and severe cavitation conditions, the maximum axial force amplitude of the nuclear reactor coolant pump appears in the two times blade frequency, and in the broken cavitation condition, the maximum axial force amplitude appears at the shaft frequency. When the eccentricity is 20 mm, the axial force fluctuates most under critical and severe cavitation conditions, and when the eccentricity is 10 mm, the corresponding axial force is smaller than that of the original scheme. When the eccentricity is 5 mm, the axial force on the impeller is the smallest, but the amplitude is the largest under the condition of fracture cavitation. Full article

This paper studies the influence of added mass, centrifugal force and hydraulic load on natural frequencies of a Reactor Coolant Pump (RCP) impeller. A series of comparative studies under different conditions were carried out on a modal test bench and a simulation platform. Modal analysis of a full-scale RCP impeller was conducted by simulation, and an improved design of impeller was proposed to prevent hydraulic resonance. These results indicated that hydraulic load increases natural frequencies of the impeller. While the centrifugal force slightly reduces them, but it is negligible. Because the distribution of hydraulic load has an effect to natural frequencies, a solution of cutting inlet edges of blades can be used to increase the natural frequency that may cause hydraulic resonance. In summary, our research shows that both added mass and hydraulic load have a significant influence on natural frequencies of the RCP impeller, and redistributing the hydraulic load can alter natural frequencies of the impeller. Full article

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. Full article