Development of Nondestructive Testing Techniques for Gas-Cooled Plasma-Facing Components

A concept for a gas-cooled plasma-facing component (PFC) has been investigated that utilizes a multijet pressurized gas (helium or nitrogen) for the extraction of heat energy. A finger-type module of the gas-cooled PFC is designed and fabricated to withstand 5 MW/m2 heat flux. Two nondestructive testing techniques, namely, (1) ultrasonic flaw detection and (2) eddy current thermography (ECT), are implemented for assessment of the curved and straight interfaces of the gas-cooled finger-type module. First, an ultrasonic technique with phased array (PA) C-scan imaging is implemented. The ultrasonic probe, PA test parameters, and test sensitivity are optimized using CIVA 10.1 simulation. Validation of the ultrasonic technique is performed on calibrated samples with reference defects with 0.5-, 1-, and 2-mm–diameter flat bottom holes. Further, metallic joints of similar (W/WL-10) and dissimilar (WL-10/Type 304 stainless steel) materials used in fabrication of the gas-cooled PFCs are investigated. Second, the ECT technique with a specially designed thermal wave excitation coil is implemented to assess the heat transfer characteristics of the gas-cooled PFC. Transient thermal profiles are obtained using COMSOL simulation for known reference defects ranging from 0% to 100% of the bond area. Experimental validation is performed on a sample with calibrated reference defects. Thermal profiles on the gas-cooled PFCs are investigated successfully. Ultrasonic testing techniques realize the size and location of defects present at the joint interfaces, and the ECT provides heat transfer characteristics, which helps to assess the quality of the multilayered gas-cooled PFCs effectively, and the obtained results are utilized for improvements in the fabrication technologies. This paper presents in detail the experimental methods, their simulations, and the results of the nondestructive tests conducted on the gas-cooled finger-type module of the PFC.