[en] Prediction of dryout point is experimentally investigated with deionized water upflowing through narrow annular channel with 1.0 mm and 1.5 mm gap respectively. The annulus with narrow gap is bilaterally heated by AC current power supply. The experimental conditions covered a range of pressure from 0.8 to 3.5 MPa, mass flux of 26.6 to 68.8 kg·m_²·s^-1 and wall heat flux of 5 to 50 kW·m^-2. The location of dryout is obtained by observing a sudden rise in surface temperature. Kutateladze correlation is cited and modified to predict the location of dryout and proved to be not a proper one. Considering in detail the effects of geometry of annuli, pressure, mass flux and heat flux on dryout, an empirical correction is finally developed to predict dryout point in narrow annular gap under low flow condition, which has a good agreement with experimental data. (author)

[en] Highlights: • A thermal-hydraulic analysis code named TSACO-HCCB TBM was developed. • The code was verified by comparing with RELAP5. • The design basis accident in-vessel LOCA analysis was performed with this code. • This article is useful for design and operation of helium cooling system. -- Abstract: In this study, a thermal-hydraulic and safety analysis code (TSACO) for helium cooling system has been developed using Fortran 90 language, and the simulation has been performed for the cooling system of the Chinese helium cooled ceramic breeder test blanket module (CH HCCB TBM). The semi-implicit finite difference technique was adopted for the solution of the dynamic behavior of helium cooling system. Furthermore, a detailed illustration of the numerical solution for heat structures and critical model was presented. The code was verified by the comparison of RELAP5 code with the same initial condition, boundary condition, heat transfer and flow friction models. The TBM inlet/outlet temperatures and pressure drop were obtained and the results simulated by TSACO were shown in good agreement with those by RELAP5. Thereafter, the design basis accident in-vessel loss of coolant accident (LOCA), was investigated for the CH HCCB TBM cooling system. The critical flow model was also verified by comparing with RELAP5 code. The results indicated that the TBM can be cooled down effectively. The vacuum vessel (VV) pressure and the mass of helium spilled into the VV maintained below the design limits with a large margin

[en] Thermohydraulics characteristics in the secondary side of AP1000 steam generator (SG) are simulated based on the porous media models. The drift flux two-phase flow model coupled with a simplified flow boiling model is utilized. The heat transfer from primary side fluid to secondary side fluid is calculated three-dimensionally during iterations. The resistances caused by downcomer, tube bundle, support plates and primary separators are considered. Three-dimensional distributions of velocity, temperature, pressure, enthalpy, density, void fraction and flow vapor quality are obtained from the calculation by using the CFD code ANSYS FLUENT. Flow-induced vibration (FIV) damage is analyzed based on the cross flow velocity over the U-bend region of the outmost U-tube. The most severe FIV damages occur at the angles of −0.544 rad on the cold side and 0.353 rad on the hot side with maximum cross flow energies of 1145.2 J/m³ and 658.9 J/m³, respectively. Fouling is expected to deposit at the bottom of tube bundle since the velocity there is close to zero. The flow vapor qualities of mixture flowing into separators vary from each other significantly, with the maximum and minimum flow vapor quality in separators of 0.659 and 0.073, which is a severe challenge to the capacity design of separators. -- Highlights: • Secondary side of steam generator is simulated with porous media model. • Heat transfer from primary to secondary side is taken into account. • Localized flow characteristics of secondary side are obtained. • Parameters to analyze FIV damage, fouling and separator load are obtained

[en] Leak rate calculation is the foundation of Leak-Before-Break (LBB) technology application in Pressurized Water Reactor (PWR). In the paper, a leak rate Mathcad calculation code with different critical flow mathematical assumptions was completed. The code calculation results were contrasted from the published experimental data. The compared results show that the code calculation results are coincident with experimental data. However, the theoretical results are greater than experimental data with different crack L/D, stagnation pressures and subcooled temperatures in case of ignoring friction effect. While the crack friction effect is considered, the calculated results are well in accordance with the experimental data. Also, the different pressure drops are obtained and studied with variations of important parameters in detail. It demonstrates that the friction effect is a significant factor and must be considered in the crack leak rate calculation. The Mathcad code can be used to calculate the crack leak rate and provide application foundation of LBB in PWR pipe system. -- Highlights: • The leak rate mathematical models of LBB were studied and modified. • Mathcad programming of leak rate calculation and comparing with experimental data. • Studies of different initial conditions and friction effect. • Formed Mathcad code can be used to calculate the crack leak rate accurately

[en] A steam generator used in the nuclear power plant is the key component to connect the primary loop to the secondary loop. The concept of the once-through steam generator (OTSG) is developed for the integrated advanced nuclear reactor because superheated steam is generated by it and thus the moisture separator is not necessary. The structure of the nuclear reactor would become compact and the reactor safety would also be improved. The OTSG mounted vertically inside the reactor pressure vessel is a countercurrent heat exchanger consisting of annulsar tubes heated bilaterally. We established the homogeneous one-dimensional flow model for analyzing the thermal hydraulic characteristics of the OTSG during the steady and transient states. For obtaining the thermal hydraulics parameters of OTSG appropriate heat transfer and friction coefficients empirical correlation equations in the different heat transfer regimes are utilized. The enthalpy and temperature profiles of the primary and secondary coolants in the steady and transients states are calculated using the simulating code developed by the model. Other important values such as wall temperatures of the inner and outer tubes are also obtained. The important issues related to the structure design and safety of the OTSG are also discussed. (authors)

[en] In the present study, thermal-hydraulics characteristics of AP1000 passive residual heat removal heat exchanger (PRHR-HX) at initial operating stage were analyzed based on the porous media models. The data predicated by RELAP5 under the condition of the station blackout was employed as the inlet flow rate and temperature boundary of CFD calculation. The heat transfer from the primary side coolant to the in-containment refueling water storage tank (IRWST) side fluid was calculated in a three-dimensional geometry during iterations, and the distributed resistances were added into the C-type tube bundle regions. Three-dimensional distributions of velocity and temperature in the IRWST were calculated by the CFD code ANSYS FLUENT. The primary temperature, heat transfer coefficients of two sides and the heat transfer were obtained using the coupled heat transfer between the primary side and the IRWST side. The simulation results indicated that the water temperature rises gradually which leads to a thermal stratification phenomenon in the tank and the heat transfer capability decreases with an increase of water temperature. The present results indicated that the method containing coupled heat transfer from the primary side fluid to IRWST side fluid and porous media model is a suitable approach to study the transient thermal-hydraulics of PRHR/IRWST

[en] In this paper, a local radial point interpolation method (LRPIM) is given to obtain the numerical solution of the coupled equations in velocity and magnetic fields for the fully developed magnetohydrodynamic (MHD) flow through a straight pipe of rectangular section with arbitrary wall conductivity. Local weak forms are developed using weighted residual method locally from the governing equations of the full MHD. The shape functions from LPRIM possess delta function property. Essential boundary conditions can be applied as easily as that in the finite-element method. The implementation procedure of LRPIM method is node based, and it doesn't need any 'mesh' or 'element'. Computations have been carried out for different Hartmann numbers and different wall conductivity. Since the energy equation is uncoupled with velocity and magnetic field for the fully developed MHD flow, the finite volume method (FVM), which is effective on heat transfer problems, is applied to solve the energy equation with the obtained velocity fields. (author)

[en] Based on lots of experimental study for liquid sodium Critical Heat Flux (CHF), and combined with the two-phase flow thermal-hydraulic characteristics and physical properties of liquid sodium, the following two-phase flow patterns, thermal-hydraulic characteristics such as incipient boiling flow, bubbly flow, plug flow, annular flow and two direction annular flow, are analyzed. From the experimental results, investigated the heat-transfer crisis mechanism of the void explosion and liquid film destroyed or local dryout when liquid sodium occurs critical heat flux are also deeply

[en] A theoretical investigation on the thermal hydraulic characteristics of a new type of passive residual heat removal system (PRHRS) for an integrated pressurized water reactor is presented in this paper. The residual decay heat of the reactor core should be removed safely through multi-interknit natural circulation loops on the occasion of normal or accidental reactor shutdown. A one-dimensional model and a simulation code are developed to theoretically predict the transient behavior of the PRHRS. It is found that the calculated parameter (such as heat transfer capacity, pressure and mass flow rate) variation trends are reasonable. The decay heat can be safely removed by the PRHRS. However, the peak value of the secondary loop pressure is higher than the expected one. A protection measure of the secondary loop pressure should be considered in the model. (authors)

[en] Highlights: • Spraying characteristics in the pressurizer of Pressurized Water Reactor were tested. • Spray droplet collector was fabricated to obtain a 2-D spray flux distribution graph. • A photography chamber was specially implemented to measure the spray drop size. • An exponent was proposed for the discharge coefficient of the pressure-swirl nozzle. • A better empirical method for Probability Density Function of drop size was proposed. - Abstract: Spraying system in the pressurizer of Pressurized Water Reactor (PWR) power plant system is of great importance for system pressure control. An experimental study on the spray characteristics, including mass flow rate, spray flux distribution, spray cone angle and drop size spectrum, was conducted. A testing loop with nine swirling nozzles was established for the study. In order to measure the spray cone angle and drop size spectrum, two original devices including a spray droplet collector and a photographic chamber were designed and employed. The former was used to collect the spray droplet along the cross-section diameter, and the latter was made to isolate and measure the targeted spray droplet. Based on the experimental data, the curves of flow rate and spray cone angle versus nozzle pressure drop were obtained. Several typical spray flux distributions were derived and the results indicated that the flux distribution changes significantly with even small pressure changes. Thus, it was proposed that instability of the spray flux distribution should be considered in the pressurizer. Based on the spray drop pictures recorded by the high speed camera, Probability Density Function (PDF) of the drop size was obtained and compared with four ‘standard’ empirical distributions. It was found that the Nukiyama–Tanasawa distribution provides a better fit to the experimental PDF of the spray drop size. The present work introduces the experimental methodology and results of spray behaviour of the nozzle in pressurizer. The work is expected to be helpful for the optimization design of spraying systems