Thermal-Hydraulic Design And Analysis Of CFETR Divertor

CFETR (China Fusion Engineering Test Reactor) is a research project to verify the feasibility of magnetic confinement fusion reactor in China. It should be tritium self-sustained by blanket aimed at getting fusion power of50～200MW. Its main parameters are major/minor radii of5.7m/1.6m and plasma current of10MA. In CFETR, divertor takes the missions of:1) controlling the plasma boundary2) exhausting heat and helium ash3) reducing the main plasma impurities. The thermal-hydraulic design of the divertor is particularly demanding because of the extreme high heat loads from the main plasma, the divertor region plasma and energetic particles.This article firstly discusses from the development of nuclear energy and the magnetic confinement fusion experimental reactor to the China Fusion Engineering Test Reactor (CFETR). The CFETR engineering models is designed on the base of the physical calculated magnetic configuration. We choose the most well developed ITER-like magnetic configuration to build the CFETR divertor. The whole divertor uses the Cassette structure and the first wall uses the Monoblock structure.The thermal hydraulic design for CFETR divertor is the key point of this article. There are totally60divertor modules in the design of CFETR that takes an angle of6°for each. All modules are divided into8groups for the design of cooling system. Each module has one main inlet pipe going through one lower port and one main outlet pipe coming back through the neighboring one. The cooling water serially go through the cassette body, the outer target, the outer baffle, the cassette body, the inner target, the inner baffle, the cassette body, the inner particle reflector, the dome, the outer particle reflector, the cassette body and then back to the outlet manifold. All the monoblock structures in first wall component are parallel cooled.It is important to do thermal hydraulic and mechanic analysis to verify that the divertor model could satisfy the engineering requirements. First of all, the hydraulic analysis shows that enlarge the diameter of the main tube, minimizing unnecessary corners and smoothing the sharps to avoid unnecessary pressure drop should be taken into consideration. Secondly, the thermo-hydraulic analysis for the divertor should consider the temperature limits for the materials, the critical heat flux margin of1.4. And the cooling water should be ensured no physical phase change during operation. And three different cooling structures (smooth tube, swirl tube with tape twist ratio of 2and4) have been studied to find the best cooling structure. And also a series of inlet mass rates are applied to the three cooling structures to define the optimal water mass rate to satisfy the design criteria. And one can note in this article that the structure with tape twist ratio of2takes the minimum cooling water of5.82kg/s which means the minimum pumping power loss of1.9KW and the most efficient cooling structure to meet the design criteria. Finally, the possibility of structure destruction caused by thermal stress should be well studied by thermal mechanic analysis. It is found that the structure with tape twist ratio of2could meet the criteria that the maximum stress is less than3Su. At the last of the article, the simulation of the divertor under the heat flux of10MW/m2is done to demonstrate that the structure with tape twist ratio of2could bear the extremely high heat flux while give a relaxed limitation.In all, compared the phenomena of the different divertor structure to the engineering criteria, the preliminary CFETR divertor structure has been designed and the manner for the coolant parameter optimization is proposed. This study provide a reference for the future CFETR divertor engineering design.