As regards access to the core shroud and to the surface to be examined, two alternatives might be considered: inspection from outside the component, moving along the so-called annulus between the reactor vessel wall and the component (OD inspection), or from the interior (ID inspection).

With a view to addressing this problem, Tecnatom has in recent years launched several projects, grouped under the generic name TEIDE, in order to develop scanners and NDT techniques achieving the maximum inspection coverage of this component.

The decision was taken to perform ID inspections, which provide the following advantages:

• Maximum inspected weld length. This avoids interferences with the jet pumps and the systems present in the annulus and affecting OD inspections. Besides, the repairs performed on in-service core shrouds in all cases imply the addition of new fixed elements on their outer surface, since the fuel assembly space must be left free.
• Reduction of inspection times and of unforeseen events: maintenance of planning schedules, reduction of personnel doses, reduced critical path time.
• High inspection accuracy and repeatability.
• Simplification of equipment positioning work (similar to the installation of fuel assemblies).

As regards inspection techniques, the decision was taken to carry out acquisition simultaneously using both ultrasonics (UT) and eddy currents (ET). The ultrasonic technique includes different sensors grouped on a single probe, providing dimensioning in length and depth of cracks open either onto the inner or outer surface (main volumetric examination).

For its part, the eddy current technique is justified by the greater accuracy it guarantees in the length dimensioning of defects open onto the scanning surface (complementary surface examination). In addition, this technique guarantees a high degree of reliability in defect detection and in real-time display.