France’s Areva NP has demonstrated a new technique and manipulator to provide off-axis inspection for cracks in boiling water reactor (BWR) core shroud welds. Areva NP said the technique, which was demonstrated during a recent outage at a US BWR, uses a phased array ultrasound technology paired with a specialised multi-axis manipulator. Craig Ranson, senior vice president of Installed Base Services at Areva Inc, said the development of the new technique and manipulator would shorten examination times and reduce radiation exposure to personnel.
In BWRs, which are single-circuit reactors, coolant water is allowed to boil in the reactor core to produce steam which is transferred directly to electricity generating turbines. Core shrouds, stainless steel cylinders surrounding the fuel inside the reactor pressure vessel, are used in BWRs to separate upward and downward flows of water. Utilities are required to regularly examine the welds in the core shrouds using ultrasound tools to inspect for cracks parallel to the core shroud weld. However, perpendicular or "off-axis" cracking can also occur. Areva NP’s new tool was developed its to examine, accurately detect and characterise all flaws surrounding the weld, whatever their orientation.