Simulation Study On Tritium Transport In Glove Box Of CFETR Based On The Typical Incidence

The China Fusion Engineering Test Reactor(CFETR)is China’s self-designed and ongoing next-generation fusion reactor project.To ensure the safety of tritium handling and operation during the fuel cycle system,CFETR has a tritium confinement system to ensure that the radioactivity level is maintained below the safety limit.In accordance with CFETR tritium multiple-confinement design principles,critical tritium-related equipment or components are set in a secondary confinement,that is,glove box,equipped with Glovebox Detritiation System(GDS).When the tritium concentration in the glove box exceeds the safety setting,the GDS will be activated,and the contaminated glove box will be detritiated by pure nitrogen purge.However,how to ensure the efficiency of the GDS system for tritium removal directly affects the consequences of a typical operational event of tritium leakage,which has not been fully studied.Therefore,the following research work is carried out in this paper based on the CFD numerical simulation software COMSOL Multiphysics.(1)Selection of the Tokamak Exhaust Processing system(TEP)typical incident and preliminary study of tritium transport process in TEP glove boxBy analyzing the tritium inventory in each system of the CFETR fuel cycle and the characteristics of TEP,referring to the accident analysis report of Thermonuclear Experimental Reactor(ITER),the glove box of the TEP system was selected as the object of this study and the initial events and related accident time sequences of TEP typical incident were developed.Based on the preliminary design parameters of CFETR,the three-dimensional transport process of tritium in TEP glove box is studied by using COMSOL Multiphysics software.By laying out spatially representative monitoring points and obtaining real-time transient information on tritium concentration at the monitoring points,a quantitative study of the transport behavior of tritium in the glove box during the whole cycle of the operational event sequence(including tritium release,alarm,pump stop,tritium removal,etc.)is carried out.(2)Proposal of ventilation detritiation efficiency parameter and analysis of the effect of GDS ventilation flow on tritium transport pracessBy analyzing the information of transient changes of tritium concentration at the monitoring points during the tritium removal stage,the concept of half-exclusion period is proposed to evaluate the detritiation efficiency of GDS.The value of half-exhaustion period reflects the tritium removal efficiency of GDS.The smaller the value of halfexhaustion period,the faster the tritium is removed from the glove box,and the higher detritiation efficiency of GDS is.The detritiation efficiency of GDS with different airflow rates is further simulated,and the reasons and mechanisms of the effect of airflow rate on the tritium removal efficiency is analyzed.It is shown that increasing the supply air flow rate can enhance the convection of the gas in the glove box and thus directly increase the detritiation efficiency of the GDS.However,when the supply air flow rate is high,it becomes less effective to continue increasing the tritium removal efficiency of the GDS by increasing the supply air flow rate.(3)Influence of different ventilation patterns on GDS detritiation efficiencyThe design principles of GDS ventilation patterns are developed by combining the glove box layout and engineering ventilation design experience.Based on this principle,a total of 25 different ventilation patterns are designed,and the detritiation efficiency of all ventilation patterns under typical incident are simulated and analyzed.The results show that,among all the patterns,the highest detritiation efficiency can be obtained with pattern A-8(the supply vent and exhaust vent are located at the diagonal ends of the top surface),and this pattern improves the detritiation efficiency by about 58%without increasing the supply air flow rate.By comparing the flow field characteristics under different pattern,it was demonstrated that a flow field with a smaller scale of back-mixing may be more efficient in the tritium removal process.The detritiation efficiency of GDS is more sensitive to the location of supply vent,and that is because the location change of exhaust vent affects the flow field near exhaust vent only,while the location change of supply vent may affect the flow field in the whole glove box.In this paper,numerical simulation method is used to investigate the tritium transport process in the glove box of the TEP secondary safety containment system of the CFETR during a typical incident.The transport process of tritium during the full cycle of the TEP typical incident sequence in the glove box is quantitatively simulated,and a more effective GDS ventilation pattern is obtained by comparing the tritium removal characteristics of 25 designed ventilation patterns.This study will provide data to support the detailed design being conducted by CFETR to ensure more efficient removal of tritium from the three-dimensional space in the case of an accidental tritium leak.