Inspections of pressure vessel head penetrations

The problem of cracks in CRDM vessel head penetrations calls for specific inspection techniques to detect potential defects in such nozzles without dismantling the CRDMs and the thermal sleeve. Using specific, thin eddy current coils, defects have been detected with a depth of less than 1 mm. Thin ultrasonic probes determined and verified crack sizes. A gap scanner is used to manoeuvre probes into the gap between nozzle and thermal sleeve. The optimised adjustment of the inspection probe by the manipulation system provides the required resolution and sensitivity. A remote inspection with the described manipulators and probes saves time and radiation dose. (orig.)