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The Steam-Water Co-Current Flow (SWCOCF) in the AP1000 Pressurizer Surge Line (PZR SL) are important phenomena during the depressurization stage of the Small Break Loss-of-Coolant Accidents (SB-LOCAs), which affect the predictions of SWCOCF pressure drop in PZR SL and safety analyses. To investigate the pressure drop characteristics of SWCOCF in the PZR SL of AP1000, a PZR SL test model made of stainless steel is designed and a test loop is also established. The test section is mainly composed of a long inclined tube with a short acrylic visual section, a whole surge line tube and a vertical section. Two experiments were conducted: the single phase water experiment and the SWCOCF experiment. The total friction factor and the full-liquid two-phase friction multiplier as well as the liquid-only two-phase friction multiplier of the PZR SL tube were obtained, separately. The research results show that: the whole surge line two-phase friction multiplier increases with the increasing of mass quality, and decreases with the increasing of pressure. Two prediction models of two-phase friction multiplier for the surge line were developed based on the Martinelli-Nelson and Lockhart-Martinelli method, respectively. The fitted full-liquid two-phase friction multiplier model and the liquid-only two-phase friction multiplier model can predict the two-phase friction pressure drop in PZR SL very well. This paper may provide contributions to the design and safety analysis of AP1000 surge line. [ABSTRACT FROM AUTHOR]

To investigate Counter-Current Flow (CCF) characteristics in the Pressurizer Surge Line (PZR SL) assembly of the large advanced passive nuclear reactors, steam-water CCF experiments are carried out on a stainless steel test section, which is a 1:4 scaled-down model of the AP1000 PZR SL assembly. The inner diameter of the test PZR SL pipe is 90 mm, which also belongs to the large-diameter pipes, as same as the prototype PZR SL pipe, in the field of Counter-Current Flow Limitation (CCFL) researches. The present steam-water CCFL experiments are conducted under normal pressure and saturated temperature, with the PZR simulator collapse water level ranging from 350 to 900 mm. CCFL becomes severer at higher steam flow rate, and the most limiting CCFL effect locates between the PZR simulator bottom head and the vertical part of PZR SL pipe. The onset of CCFL and zero liquid penetration (ZP) are two critical conditions in the CCF development process, dividing the process into three stages: Before-CCFL, Partial-CCFL, and CCFL-ZP. According to the local CCFL conditions, the development of the CCFL process is also divided into four-regions since onset of CCFL. The present steam-water CCF data are well normalized in terms of dimensionless Kutateladze (Ku) numbers, and a Ku-type empirical partial CCFL correlation is developed. The comparisons of the present CCF data and partial CCFL correlation with the CCF data and correlations of former experiment researches validate that the present empirical partial CCFL correlation is conservative to predict steam-water partial CCFL in the prototype PZR SL assembly of the large advanced passive nuclear reactors. [ABSTRACT FROM AUTHOR]

For the previous experiments of entrainment at T-junction, the air–cold water two-phase flow is always selected as working medium, and the theoretical models of liquid entrainment are established mainly based on the experimental data of air–water entrainment through a small break. The saturated steam–water entrainment experiments are gravely insufficient, especially the steam–water experiments of entrainment through a large size branch are even fewer. Hence, a scale-down experiment of steam–water entrainment at T-junction has been conducted referring to liquid entrainment through ADS-4 (Fourth Stage Automatic Depressurization System) in AP1000 nuclear plant. The steam–water experimental results are comprehensively compared with the results of the previous similar air–water experiment: The visualization research shows that the same entrainment phenomena can be observed including intermittent flow entrainment, stratified flow entrainment and annular flow entrainment; The transition conditions between the two entrainment phenomena have a little difference but can be negligible; The comparison of experimental data of entrainment onset and stable entrainment indicates that the experimental data of steam–water and air–water have the same change tendency, and the air–water correlation can agree well with the steam–water data. Hence, we can make a conclusion that effect of different working mediums on liquid entrainment is negligible. In addition, based on the analysis of model formation, we suppose that effect of the system pressure on entrainment can be neglected under 0.22 MPa. [ABSTRACT FROM AUTHOR]

Abstract: This work presents the experimental research on the steady laminar natural convection heat transfer of air in three vertical thin rectangular channels with different gap clearance. The much higher ratio of width to gap clearance (60–24) and the ratio of length to gap clearance (800–320) make the rectangular channels similar with the coolant flow passage in plate type fuel reactors. The vertical rectangular channels were composed of two stainless steal plates and were heated by electrical heating rods. The wall temperatures were detected with the K-type thermocouples which were inserted into the blind holes drilled in the steal plates. Also the air temperatures at the inlet and outlet of the channel were detected. The wall heat fluxes added to the air flow were calculated by the Fourier heat conduction law. The heat transfer characteristics were analyzed, and the average Nusselt numbers in all the three channels could be well correlated with the Rayleigh number or the modified Rayleigh number in a uniform correlation. Furthermore, the maximum wall temperatures were investigated, which is a key parameter for the fuel’s integrity during some accidents. It was found that even the wall heat flux was up to 1500W/m2, the maximum wall temperature was lower than 350°C. All this work is valuable for the plate type reactor’s design and safety analysis. [Copyright &y& Elsevier]

• The critical Reynolds number increases only due to the viscosity decreases with increasing temperature. • The influence of transverse power distribution on friction factor is small. • The average Nusselt number is affected by the form of the transverse power distribution. • 15 correlations are evaluated for the heat transfer data. • New heat transfer correlations for laminar and transition region are developed. Characteristics of single-phase convective heat transfer in a rectangular channel are reported for heated and non-heated conditions. Results indicated that the friction factors were basically the same in the laminar region. However, in the transition and quasi-turbulent region, the heated friction factor was slightly lower than the non-heated values, and the value of non-uniform heating was slightly higher than that of uniform heating. The transition started critical Reynolds number increased from 2700 without heating to about 3000 with heating only due to the viscosity decreased with increasing temperatures. Due to the transition started and ended Reynolds number increased simultaneously under heating, the width of flow transition was almost the same as that without heating. The transverse power distribution influenced the average Nusselt number of the channel, although measured differences were small for uniform and non-uniform heating conditions. For the heat transfer data under uniform heating conditions obtained in this study, 15 correlations were evaluated. It is found that the existing correlations underestimated the experimental data for Re < 3000 and overestimated the data for 3000 < Re < 6000. A large database of heat transfer in rectangular channels including the experimental data obtained from this study and other researchers' work was established, and new heat transfer correlations for laminar (Re < 3000) and transition (3000 < Re < 10000) flows were developed. The Dittus-Boelter correlation was confirmed to provide a good prediction for the heat transfer for Re > 10000, with almost all data being within ±20% errors. [ABSTRACT FROM AUTHOR]