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FEM simulation for the qualification of ITER first wall components

The first wall components consist of beryllium (Be) on the surface, high strength copper as heat sink material (CuCrZr), and stainless steel as structural material. Electron beam high heat flux (HHF) testing represents one of the most appropriate methods to qualify the design and manufactory techniques of the component.

Due to the toxicity of Be, special security considerations should be taken into account. Practically, a sophisticated temperature measurement system is installed to trigger a shutdown process during testing if the Be surface temperature reaches a certain level, with the purpose of avoiding Be evaporation. However, it is helpful if the potential temperature can be calculated before testing. The finite element method (FEM) simulation is a proper way to solve this problem. It is feasible to predict the acceptance of the testing conditions without performing any HHF test.

Besides, 3D thermo-mechanical simulation provides the stress and strain distribution of the mock-up during testing, which is used to predict the failure trigger of the mock up. Figure 1 shows the temperature distribution calculated by FEM for the demonstration mock up loaded with 2 MW/m² for 30 s with coolant water velocity of 3 m/s and coolant temperature of 70 °C. The result shows that a maximum temperature of 370 °C is achieved at the Be top surface. Figure 2 shows the equivalent stress distribution of the MU loaded with 2 MW/m² for 30 s, which indicates that the maximum equivalent stress (588 MPa) occurs between the middle tile (Be2) and the adjacent CuCrZr joint.

The high stress concentration indicates the joining corner is prone to being the starting point of failure. This prediction is in a very good agreement with experimental results. The picture at the top-left of figure 2 is taken by infrared camera and shows the mock up during the experiment. It shows the overheating of the predicted failure location at the corner of the middle tile Be2.

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Temperature distributionFigure 1. Temperature distribution of demonstration mock up loaded with 2 MW/m² for 30 s. Cooling water parameters: pressure 2 MPa; velocity 3 m/s; temperature 70 °C.

Equivalent stress distributionFigure 2. Equivalent stress distribution of MU under elastic assumption calculated by FEM. The infrared image of the failed MU (top-left) indicates the overheating of the tile Be2 at the corner.