2010

Pitkänen, Jorma; Lipponen, Aarne

The surface inspection of thick copper electron beam (EB) welds plays an important role in the acceptance of nuclear fuel disposal. The main reasons to inspect these components are related to potential manufacturing and handling defects. In this work the data acquisition software, visualising tools for eddy current (EC) measurements and eddy current sensors were developed for detection of unwanted defects. The eddy current equipment was manufactured by IZFP and the visualising software in active co-operation with Posiva and IZFP for the inspections. The inspection procedure was produced during the development of the inspection techniques. The inspection method development aims to qualify the method for surface and near surface defect detection and sizing according to ENIQ [1]. The study includes technical justification to be carried out, and compilation of a defect catalogue and experience from measurements within the Posiva's research on issues related to manufacturing. The depth of penetration in copper components in eddy current testing is rather small. To detect surface breaking defects the eddy current inspection is a good solution. A simple approach was adopted using two techniques: * higher frequency was used to detect surface defects and to determine the dimensions of the defects except depth * lower frequency was used to detect defects having a ligament and for sizing of deeper surface breaking defects. The higher frequency was 30 kHz and the lower frequency was 200 Hz. The higher frequency probes were absolute bobbing coils and lower frequency probes combined transmitter - several receiver coils. To evaluate both methods, calibration blocks were manufactured by FNS for weld inspections [2]. These calibration specimens mainly consisted of electron discharge machined notches and holes of varying shapes, lengths and diameters in the range of 1 mm to 20 mm of depth. Also one copper lid specimen with 152 defects was manufac-tured and used for evaluation of weld inspection. Several copper welds have been measured to assess the performance of the eddy current inspection for detection of surface defects. Some metallographic studies to identify the origin of the indications will also conducted, and the results will be reported later in conjunction of the eddy current measurements. The results show the capability of the developed eddy current measurements to detect and size surface defects to 10 mm depth and as well as to see indications having ligament up to 5 mm. This seems reasonable according to the re-sults of EC-modeling.