Simulation Design And Thermal Hydraulic Characteristics Study Of ADS Upward Spiral Flow Windowless Spallation Target

Spallation target is the key coupling component of accelerator driven sub-critical system(ADS),which determines the power level of the overall system and maintains the security and stability of the system.Liquid metal windowless spallation target(referred to as windowless target)has potential advantages in thermal transport and is a more advanced candidate target for ADS.The formation method of a free surface in windowless target affects the distribution characteristics of the internal flow field,and then determines the power level of the target system.Liquid metal windowless spallation target based on upward spiral flow(referred to as upward spiral flow target,UST)is a new type conceptual design scheme of ADS windowless target,which employs a stationary impeller to generate upward spiral flow.The upward spiral flow sprays outward under centrifugation and forms a free surface.In this work,simulation design and thermal hydraulic characteristics study of UST have been carried out by using the combined methods of computer-aided design modeling and computational fluid dynamics analysis,and the combined methods of numerical simulation and experiment verification.By studying the regulation effects of UST structures on stagnation zone below the free surface,two types of optimized targets are finally established based on the preferred target structures and the corresponding structural parameters.Compared with the initial target,the optimal targets have smaller stagnation zone and better thermal transport performances.The main research contents are as follows:1.The regulation effects of the structural parameters on the distributions of the internal flow field and the stagnation zone are studied for each functional section of UST.The analysis for the impeller shows that the impeller has a very significant regulation effect on the flow field distribution in the target.The center shaft of the impeller mainly plays a role in guiding flow,and the blades of the impeller mainly play a role in generating spiral flow.The analysis for the transition section shows that the length of the transition section should be selected to be consistent with the incident depth of the beam.The analysis for the outlet section shows that the structural parameters of the expanding tube have little influence on the internal flow field distribution and can be adjusted flexibly in the specific range of model setting according to design requirement.Through comparative analysis,a preliminary target UST-A is established base on the preferred structural parameters of each functional section.Compared with the initial target,UST-A can reduce the volume of the stagnation zone by about 79%.2.To verifiy the simulation design methods,an experimental testing target was manufactured with the same geometry of UST-A,and a visualized water experimental loop was built to carry out hydraulic experiments.Through the comparisons between experiments and simulations,under the current working conditions,the experimental results are basically consistent with the simulation results,and the flow states observed in the experiments are also consistent with the simulation predictions.Although there are some uncertainties in the numerical simulations,the numerical results can reproduce the actual free surface flow process in UST,which shows that the current simulation methods have certain effectiveness and reliability.3.In order to further reduce the stagnation zone,structural optimizations are performed for the transition section and the outflow section.A special target is designed by adding a necking tube under the expanding tube in the outlet,which makes the fluid speed up at the necking tube and then spray out at the outlet of the expanding tube.The optimized target can significantly improve the flow field distribution and greatly reduce the stagnation zone under the free surface.The diameter of the necking tube is selected as 80%of the inlet diameter,which not only reduces the stagnation zone,but also ensures the effective beam action area.The structural parameters of the expanding tube have little effect on the distrbutions of the flow field and the stagnation zone,and can be selected according to design requirements.Finally,an optimized target UST-B is established base on the preferred target geometry and the structural parameters of the necking tube and the expanding tube.Compared with UST-A,UST-B can further reduce the volume of the stagnation zone by about 69%.4.For UST-A and UST-B,the whole velocities of the fluid in the free surface zone increase with the inlet flowrate increasing in the range of 6?9 m~3/h,and the sizes of the stagnation zone decrease accordingly.The current flowrate range is suitable for UST to form stable free surface and flow field.It can be considered that the target has good applicability of flow conditions.The variations of the flow field and the stagnation zone are not obvious after expanding the integral sizes of UST-B,which reflects the target has better extensibility.Based on UST-B,the collaborative analyses of the outer target tube and the inner target tube are carried out.Several deflectors are added on the expanding tube of the inner target tube to restrict the flow direction and weaken the influence of the external target tube.The new structure can reduce the entirety sizes of the target and make the structure more compact.As a result,the integrated structure of UST-B is established.5.The deposition heat distributions in UST-A and UST-B by spallation reaction under different beam conditions are calculated by using the toolkit GEANT4.Then,the coupling simulations of the flow field and the temperature field are carried out by loading the deposition heat.The energy and the distribution of the beam determine the action range of the beam-target coupling zone area and the distribution of deposition heat.The high temperature fluid region in the target is located in the stagnation zone when circular beam is applied.The use of annular beam can greatly reduce the fluid temperature rise.For the same power level of the beam,UST-A has lower deposition heat power density and lower temperature rise than those of UST-B,because the diameter of the beam printfoot applied to UST-A is larger than that of UST-B.For the same power density of the deposition heat,UST-B has a lower temperature rise than UST-A.To ensure the same beam condition,UST-B needs to expand the integral target,which will increase the space occupation of the target.In general,the optimized targets are obtained by studying the regulation effects of the UST structures on the distributions of flow field and stagnation zone.Then,based on the optimized targets,the flow field performances and the thermal transport performances are analyzed,while the flow conditions and the beam conditions are evaluated.The research achievements have engineering application prospects.