Study On Bubble Distribution And Movement Behavior Of Lead Based Reactor Under SGTR Accident

Lead-cooled fast reactor had become one of the most promising Generation IV reactor types due to its good transmutation potential and nuclear fuel value-added ability.Due to the common pool structural arrangement of lead-cooled fast reactor,the complex and changeable thermalhydraulic phenomena in the primary circuit may lead to the Steam Generator Tube Rupture(SGTR).The large number of bubbles generated by the direct contact of the working medium in the primary and secondary loop may increase the void fraction inside the core or affect the heat transfer capacity of the local area,thus threatening the normal operation of the reactor.Therefore,it is necessary to analyze the motion behavior characteristics of bubbles inside the reactor.This paper mainly studies the motion and regional distribution of bubbles generated in the Steam Generator Tube Rupture accident.The research object is the natural circulation lead-cooled fast reactor SNCLFR-100,which is solved by constructing the three-dimensional model of computational fluid dynamics method.Based on the simulation results,the bubble distribution law is summarized.By changing the height and orientation of the leakage point,the bubble motion behavior characteristics,bubble size distribution and bubble area distribution are compared and analyzed.The main research contents and conclusions are as follows :(1)Based on the SNCLFR-100 three-dimensional model of natural circulation lead-cooled fast reactor,the accuracy of computational fluid dynamics method for predicting the flow and heat transfer process of leadbased coolant is verified,and the turbulence model and turbulent Prandtl number model suitable for simulating the coolant flow and heat transfer of the lead-cooled fast reactor are optimized.The deviation between the calculated results under different models and the reactor design data is within ± 5 %,and the relative error between the calculation results and the design values is characterized by dimensionless numbers θ.After comprehensive consideration,the calculation model combining the standard k-ε turbulence model with the Jischa turbulence Prandtl number model is selected for subsequent numerical simulation.(2)According to the bubble floating terminal velocity,the influence of changing the drag coefficient calculation correlation on the correctness of the DPM discrete phase model is evaluated,and the trajectory tracking of the bubble motion in the primary loop under the SGTR accident of the leadcooled fast reactor is realized by using the DPM model,so as to study the influence of different drag calculation models on the bubble motion.According to the calculation formula of bubble terminal velocity,the correctness of the DPM model is verified,and the boundary conditions and numerical solution methods are set according to the actual working conditions of the natural circulation lead-cooled fast reactor.The different drag coefficient models are compared and analyzed by numerical simulation method,and bubbles on each monitoring surface are extracted by probabilistically selecting a more conservative drag model to characterize the force of bubbles following the coolant,which then lay a theoretical foundation for the subsequent analysis of the bubble motion law.(3)According to the verified calculation model and numerical method,the characteristics of bubble motion and bubble retention are studied.The effects of different heights and orientations of leakage points on the characteristics of bubble motion behavior are compared and analyzed from the perspectives of bubble trajectory tracking,bubble size distribution and bubble retention probability in each region.The conclusions are as follows : Firstly,with the increase of the height of the leakage point,the number of bubbles entering the core decreases under the middle condition,while the number of bubbles entering the core increases under the inner condition.The change of the height of the leakage point has little effect on the side and outer conditions.Secondly,the motion behavior of bubbles of different sizes is also affected by the height of the leakage point.The probability of small-sized bubbles entering the core inside and outside will increase with the increase of height,but the middle condition shows the opposite trend,and the side condition is less affected.For medium and large-sized bubbles,there will be more bubbles accumulated under the horizontal partition under the side condition.Finally,the probability of bubble retention in each region is analyzed.The overall bubble entering the core maintains a decreasing trend with the increase of height,and the bubbles retained in the lower chamber will increase accordingly.For different positions at the same leakage point height,the probability of retained bubbles in the lower chamber changes little.In the remaining areas,the central and inner working conditions will reach the peak of bubble retention faster,and the outer working conditions will continue to increase.In summary,this paper studies the characteristics of internal bubble motion under SGTR accident of natural circulation lead-cooled fast reactor,and compares and analyzes the influence of different leakage point heights and orientations on it.The results have certain reference value for the subsequent study of the influence of increasing core void fraction.