The dispersion plate fuel assembly, owing to its favorable characteristics of low temperature gradient, high stability, and excellent thermal conductivity, has become a focal point in the research of novel high-performance fuel elements. However, the current literature lacks a comprehensive understanding of the fuel plate’s performance, particularly with regard to the bubbling phenomenon in the fuel plate cladding. In this study, we have implemented a fission gas release model, building upon previous analyses of fuel plate performance under steady-state operation. By comparing our calculation results with the Forsberg-Massih model, we find a close correspondence in trends, thereby validating the accuracy of our computational approach. Furthermore, we utilize the upgraded FROBA-PLATEs code to predict the blistering behavior of fuel plates under specific quasi-steady-state conditions. Our results demonstrate that the occurrence position and threshold temperature of blistering in the fuel assembly can be precisely predicted using this approach.

Application research of two new liquid entrainment models for separately predicting the beginning of entrainment and branch entrainment quality is performed which is a continuation of previous experimental and theoretical studies on the entrainment at T-junction. The new onset entrainment model and branch quality model are developed on the basis of the scaling experiment for studying ADS-4 entrainment phenomenon in AP1000 plant, and the two new models along with previously published entrainment models are compared. The results show that previous models in the background of entrainment through a small break of primary pipe are not suitable for predicting the entrainment through a large size branch (e.g. ADS-4 pipe), while the two new models have a larger applicability. Also, the new entrainment models are written into the RELAP5 code, and then a typical 2-in SBLOCA transient in AP1000 is simulated separately by the modified RELAP5 and the original RELAP5 to further discuss the applicability of new models for the simulation of entrainment through ADS-4. The results show that the modified RELAP5 can get more reasonable simulation results. In view of original RELAP5 overestimated core coolant inventory, the modified RELAP5 can get a conservative core coolant inventory. Hence we can conclude that the new entrainment models are more suitable for the simulation of entrainment through ADS-4. (C) 2017 Elsevier Ltd. All rights reserved.

With the T‐junction formed by the fourth stage automatic depressurization system (ADS‐4) and hot leg in AP1000 nuclear power plant as object of study ,a small‐scale experiment research on entrainment at T‐junction was performed .The visualiza‐tion research indicates that the entrainment phenomena through a large size branch are apparently different from those through a small branch .Two entrainment mechanisms could be found in the stratified flow entrainment area .Intermittent flow entrainment tends to occur at a lower Froude number and a lower gas chamber height .Annular flow entrainment always arises at a higher Froude number .Also ,the experimental research shows that the reverse flow is observable in a large size branch inlet .The geometry of the branch has an important effect on the onset entrainment .In addition ,liquid cross‐flow does not seem to affect the onset entrainment .

The onset entrainment and stable entrainment for T-j unction composed of a large downward-oriented branch and a horizontal main pipe were researched based on visualization experiment.The gas entrainment experiment results were compared with the calculating results from RELAP5 .The experimental results indicate that the forma-tion of vortex at the onset entrainment is similar with the previous research results.A new vortex-free entrainment formation is observed during stable entrainment. The entrainment quantity of gas has linear relation to the pressure difference.The entrain-ment quantity of gas decreases with the increase of pressure difference between the branch and the horizontal main pipe.

An experimental and theoretical study was performed for establishing the model of liquid entrainment at T‐junction consisting of hot leg for AP1000 nuclear power plant and ADS‐4 pipe , including onset entrainment and stable entrainment models . Based on the experimental and theoretical analyses ,onset entrainment model and steady‐state entrainment model were established ,which accord with experiment data well .The influence of entrance length on entrainment was discussed to determine the entrance length of the test section . The effect of liquid flow on onset entrainment and stable entrainment was analyzed ,and the experiment results show that the effect of liquid flow on entrainment through ADS‐4 pipe can be neglected .

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. (C) 2015 Elsevier Inc. All rights reserved.

Experimental and theoretical studies have been performed for entrainment at T-junction consisting of hot leg and ADS-4 pipe. Research of basic influence factors on onset entrainment and stable entrainment is conducted and the effects of gas chamber height and gas Froude number on entrainment are discussed on the basis of experimental data. Based on visualization research, the flow regime in the main pipe is recorded by high-speed camera. Three kinds of entrainment phenomena including stratified entrainment, annular entrainment and intermittent entrainment can be clearly found, and feature of each phenomenon is summarized. Also, Onset entrainment model is established and accords with experimental data well.

An experimental and theoretical research has been performed for liquid entrainment at T-junction consisting of hot leg and ADS-4 pipe in view of the insufficiency of existing studies. Based on visualization research, three kinds of entrainment phenomena including intermittent entrainment, stratified entrainment and annular entrainment are clearly observed, and the feature of each flow regime is summarized and recorded by high-speed camera. Also, the flow pattern map is plotted from the experimental data to indicate the transition conditions of different flow regimes. For the purpose of modeling and expanding previous research, the influence of entrance length on entrainment is discussed on the basis of two different test sections. The effect of liquid flow on onset entrainment and stable entrainment is analyzed, and experiment results show that the effect of liquid flow on entrainment through ADS-4 pipe can be neglected. Also, onset entrainment model and branch quality model are established and accord with experimental data well. (C) 2014 Elsevier Inc. All rights reserved.