Transient Study Of In-box LOCA In Dual-Functional LeadLithium Blanket

The helium-cooled lead lithium blanket is considered as one of the candidate blanket concepts selected for the fusion DEMO reactors and beyond,which has the advantages of simple structure,strong heat removal capacity and high tritium breeding ratio.However,due to the harsh environment such as high-energy neutron irradiation,high thermal load and great pressure gradient,there is a high possibility that one or some of the thousands of coolant pipes will break in the breeding zone,which is so-called In-box Loss of Coolant Accident(In-box LOCA).When the accident occurs,high pressure helium rapidly injects into the PbLi channel,creating a complex two-phase flow and pressure shock that may cause the peak pressure to exceed the design limit and threaten the integrity of the blanket structure.Therefore,it is of great significance to study the transient process of in-box LOCA to improve the safety of the blanket and avoid the leakage of radioactive material.In this paper,by means of numerical simulation and experiment,the transient process of high-pressure He jection into PbLi in Dual-Functional Lead Lithium(DFLL)blanket was studied,mainly including:1)A Two-way Fluid-Solid Intereaction method is constructed based on He and PbLi two-phase flow:first,Volume of Fluid(VOF)method is used to realize the tracking of the interface of He and PbLi two-phase flow.Then,based on the theory of Fluid-Solid Intereaction,a Two-way Fluid-Solid Intereaction analysis method is constructed by using CFD software,which is applicable to describe the in-box LOCA.The compressible model is used to simulate the propagation process of pressure wave.Through the comparison and verification between the calculation examples of shock wave propagation and the calculation examples of He and PbLi two-phase flow,the capture ability of pressure wave propagation between He and PbLi and the simulation ability of two-phase propagation are verified numerically.2)Pressure wave propagation experiments of high-pressure He injection into PbLi are conducted,and the above method is verified based on KYLIN-II-S,a safety loop experiment platform for liquid heavy metals.The experimental data of pressure wave propagation of PbLi injected by high pressure He(>8 MPa)are obtained.It was found that a significant Fluid-Solid Intereaction effect was generated during the impact process in the experiment,and the pressure wave presented two stages:rapid shock stage and steady growth stage.The rapid shock stage lasted about 0.064s,forming pressure peaks greater than 6 MPa for several times.The experimental conditions were simulated by using the Two-way Fluid-Solid Intereaction method,and compared with the method without considering Fluid-Solid Intereaction,the results showed that the Two-way Fluid-Solid Intereaction method is in better agreement with the experimental results.3)The propagation characteristics of pressure waves and structural responses of internal rupture accidents are studied:based on the above Two-way Fluid-Solid Intereaction method,the Fluid-Solid Intereaction analysis model of DFLL blanket is established to study the propagation of pressure waves and structural transient response under in-box LOCA in DFLL blanket.The study found that after the rupture occurred,the blanket experienced three stages of pressure step up,pressure shock and pressure gentle,and the peak pressure shock occurred in the region with high resistance zone in blanket(corner,entrance and exit),resulting in the peak pressure reaching twice of the inlet pressure of He gas.Meanwhile,the influence rules of different fracture positions and sizes on structural stress are analyzed,and the corresponding safety design improvement Suggestions are put forward.4)The characteristics and consequences of the two-phase flow of in-box LCOA is studied:based on the model of Two-way Fluid-Solid Intereaction of DFLL blanket,analysis of the characteristics and consequences of the two-phase flow after the in-box LOCA are studied.It found that within 0.3 s after the in-box LOCA,the volume fraction of He in the PbLi flow channel of the blanket was more than 60%.At this time,the fusion reactor has not been shut down in time(response time is about 3 s).Before the reactor completely shuts down,the nuclear thermal deposition load on the magnet system increases exponentially,so it is recommended to give a margin in the blanket shielding design.In the process of high-pressure He injection,due to the repeated oscillation of the pressure in the blanket module,the PbLi will reverse flow to the he flow channel.This process lasts only about 4 ms,and no blockage will be formed.In this thesis,according to the research approach of "Two-way Fluid-Solid Intereaction method→experimental verification→simulation of transient process of in-box LOCA",the characteristics of pressure propagation and structural response of DFLL blanket is illuminated.This paper explores the characteristics of He and PbLi two-phase flow and its influence on shielding performance,and puts forward corresponding improvement Suggestions,which provide strong support for the safety design and performance improvement of He-cooled lithium lead liquid blanket.