Phased Array Techniques - Benefit in Efficiency and Effectiveness for Nuclear and Non-Nuclear Applications
E. Fischer, G. Engl, F. Mohr, H. Diehl, Siemens, Erlangen, Germany
ABSTRACT
Starting with the successful blind test and the subsequent examinations of BWR-RPV-feedwater nozzle inner radii nozzle bore from the O.D. surface, the application of the phased array techniques for the inspection of reactor components has been consequently extended over the past decade. Up till now, a large variety of ISI problem areas was covered by the implementation of phased array techniques. In most of the cases the driving force to implement this (at least at first view) complex technology was twofold: This technology offered a considerably higher reliability of the inspection in terms of detection, sizing and characterization accompanied by savings in inspection time - mostly in conjunction with a considerable reduction of the radiation exposure to the inspection personnel. The last two criteria can be translated into reduced cost of the examination, even if the price of the UT-equipment and of the individual probes for phased array applications is considerably higher when compared with the conventional "equivalent". Some examples provide solid proof for these considerations:
The nozzle inner radius of the ECCS piping into the (ferritic clad) Main Coolant Piping.
The control rod ligaments in the PWR-RPV top head respectively of the BWR-RPV bottom head.
Consequently, also the examination of the adjacent circumferential weld(s) between top/bottom head dome and top/bottom flange was enhanced and extended by the use of phased array techniques.
Other examples for the successful application of phased array technology are: BWR-RPV-ISI from I.D. and O:D. surfaces, RPV Core Shroud, RPV Bottom Ligaments, Pressurizer Ligaments and Nozzle-to-Dome welds.
Most recently, complicated geometries together with the problem of stainless steel weld inspection in BWR pipe to nozzle areas posed a very difficult ISI problem which could only be solved satisfactorily with the phased array approach.
A most remarkable milestone for the phased array application was the successful examination of the 2 RPV's (W/Framatome design) in Koeberg, South Africa. The on vessel time for the entire examination (10 year scope and entire core region of the shell) was 7,5 days. This and the following topics are covered by separate papers:
The phased array techniques have also been implemented into the ISI of VVER components, like the RPV (from I.D. and O.D. surfaces) and S/G collector flanges. The pioneer plants for these activities are Paks (Hungary) and Bohunice/Mochovce (Slovakia).
Publication Source: First International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components , 20 - 22 October 1998, Amsterdam, Netherlands. Held by the Joint Research Centre of the European Commission. Publisher:Woodhead Publishing Limited
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