Neutron diffraction measurement of residual stresses in an ITER-like tungsten-monoblock type plasma-facing component

Abstract

Neutron diffraction measurements have been carried out for non-destructive characterization and numerical predictions validation of the residual stresses in a mock-up of the ITER-like divertor target plasma-facing component, made by hot radial pressing of 4 tungsten blocks to a CuCrZr cooling pipe via a soft copper interlayer. The neutron diffraction measurements were carried out, at room temperature, at FRM II reactor in Garching. Stress-relieved W and CuCrZr were examined as reference state before joining. The 3D stress tensor was determined in one of the two external W-blocks and CuCrZr pipe segments, scanning the mock-up from the outer surface of the W block towards the inner wall of the CuCrZr pipe with the interval of 0.4–0.5 mm. A residual stress distribution from tension to compression through the bonding line is detected, as expected from the requirement of force balance. Except at the interlayer, stresses well below 100 MPa are found, confirming the good fabrication quality of the investigated monoblock. These experimental results are comparable with the FEM-based numerical prediction, but at the interlayer and inside the pipe a sharper spatial resolution is needed for the neutron diffraction measurements to catch the hoop and axial stress gradient profile.