Study On Inner Fuel Cycle And Tritium Transport Simulation For CFETR Tritium Plant

In order to realize the early application of fusion energy,the design and construction of fusion reactors are being steadily promoted internationally.The baseline fusion power of Chinese Fusion Engineering Testing Reactor(CFETR)designed by our country is 500 MW,and the start-up tritium fuel inventory is about 2 kg.Tritium resource is extremely scarce and expensive,in addition to reducing the tritium inventory in the inner fuel cycle of CFETR tritium plant,it should process and recycle a large amount of tritium fast to reach the tritium self-sufficiency target.As an important radioactive source term,tritium is very easily release to gloveboxes and rooms of tritium plant due to tritium permeation and leakage which cause pollution,it not only causes the loss of valuable tritium resource,but also directly affects the safety of workers and the public.Thus,accurate simulation of tritium transport processes for fusion reactor becomes critical,it especially needs the research on accidental tritium release and tritium removal in tritium plant.From the perspective of in-pile tritium safety,this thesis has performed the inner fuel cycle simulation of CFETR tritium plant to estimate tritium source term in normal operation and research on fast fuel recovery.And we have carried out the tritium transport simulation of inner fuel cycle under typical incident and accident conditions to estimate tritium leakage,confinement,migration and removal in rooms of CFETR tritium plant.Firstly,we elaborated the fuel cycle theory and System Dynamics method,the systematic tritium fuel cycle model has been built and compared with tritium fuel cycle outcomes of Chinese Helium Cooled Ceramic Breeder Test Blanket System(CN HCCB-TBS).Then,we described the tritium transport theory,Finite Difference and Finite Element methods,the component-level tritium transport model has been built and compared with tritium incidental leakage results of International Thermonuclear Experimental Reactor(ITER).The room tritium transport model has been built and compared with experimental and simulated tritium accidental leakage results of tritium handling main cell at American Tritium System Test Assembly(TSTA).Verified the correctness of the systematic tritium fuel cycle,component-level and room tritium transport models,a set of accurate models have been provided for inner fuel cycle,tritium leakage and tritium transport simulation and safety analysis in room of CFETR tritium plant.Then,we brought the new technology of Direct Internal Recycling(DIR)into the inner fuel processing for CFETR tritium plant.Based on the dynamic system simulation code Simulink,the mean residence time model of inner fuel cycle of CFETR tritium plant has been built.Tritium inventories and permeation of all subsystems were calculated and we estimated the influence of the front-end DIR design(shortcut set before the Tokamak Exhaust Processing System TEP),rear-end DIR design(shortcut set through the first stage of TEP),DIR fraction and tritium processing time on tritium source term and safety.The research results show that besides the Storage and Delivery System(SDS),the largest tritium inventory in tritium flows of tritium plant is TEP.The front-end DIR design will retrieve more tritium than the rear-end DIR design to SDS,and it reduces the tritium inventories and permeation of vacuum pump in main processing loop and TEP.The front-end DIR design has obvious advantages.Thus,this thesis suggests appropriate use of the front-end DIR design to optimize the inner fuel cycle of CFETR tritium plant.Given the baseline tritium breeding rate(TBR=1.2),it is further evaluated that the minimum initial start-up amount of CFETR is 569.7 g.Based on the Finite Difference method,the tritium transport code EcosimPro has been used to simulate the three-stage fuel treatment process of TEP which is one key system in the inner fuel cycle of CFETR tritium plant with more detail component-level models.The tritium treatment status and tritium distribution of each sub-component were obtained,and the tritium processing performance of TEP was evaluated.The double-ended guillotine break infrequent accident of the TEP tritium processing line was selected as the fuel cycle incident in the CFETR tritium plant to simulate the tritium transport status of the glove box and the room,the TEP isolation response,and the safety containment feature of the secondary barrier glove box and its detritiation system were obtained.The research results show that the overall decontamination factor of TEP three processing stages reaches?2.6 × 108 which is able to meet the design target of tritium removal performance.Due to the secondary containment of the glove box and the effective tritium removal,the double-ended rupture of the TEP tritium processing pipe in incident will not cause major radiation leakage.Finally,in order to study the tritium transport behavior in the tritium plant room under accident condition,the tritium leakage caused by the simultaneous break of the TEP tritium processing pipeline and glove box was selected furtherly as a limiting accident in the inner fuel cycle of CFETR tritium plant.Based on the code COMSOL Multiphysics,a three-dimensional model of the TEP room was established,and the tritium migration and tritium removal behavior simulation of the room under accident condition has been carried out.The effect of various key factors such as room ventilation design,humidity condition,tritium gas and tritated water isotope exchange rate,and wall materials on tritium removal were evaluated.The research results show that in the event of an accident,it works better to operate the detritiation system with maximum ventilation ratio or increase the air outlet duct.Setting the air outlet duct on the top reduces the tritium concentration by about 25%compared to that on the side,which can reduce the downward accumulation of tritium in the room.Without changing the total ventilation,adding an air outlet can reduce the tritium concentration in the room by about 50%.With the greater isotope exchange rate,the more tritiated water is produced.From the perspective of in-pile tritium safety,the research work in this PhD dissertation has established a simulation process and method of three-level containment tritium cycle and transport behaviors from the tritium plant fuel cycle system to the key components,and finally to the tritium plant room.The tritium source term and tritium leakage safety analysis under normal operation and transient conditions have been studied systematically,and the internal fuel cycle and tritium safety containment design optimized,it can provide a certain reference for the tritium self-sufficiency and tritium safety research of fusion reactors.