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SPECIAL FEATURE
Robotics Enable Corrosion Inspection Inside Nuclear Reactor
XTIKM ]VLMZ UWZM LQNÅK]T\ KWVLQ\QWV[¸ although the NRU is shut down during in-service inspections, the calandria vessel [\QTT KWV\IQV[ N]MT ZWL[ IVL PMI^a _I\MZ¸ and the inspection tools must be precisely positioned, the decision was made to develop a motorized, software-controlled robotic arm and interchangeable inspec- tion tools, Zeller comments.
Designing Robotics for NDT Inspection Instead of relying on manually oper- ated levers and pulleys for motion and position, the robotic inspection system is designed to be completely automated, so that every single operation that an inspector would typically perform during an NDT assessment is automatically ex- ecuted by the robotic arm and the NDT inspection tool at the end of the arm (known as an end effector or inspection
head). The computerized robotic arm is moved and positioned using electric mo- tors that are controlled by motion control software specially designed for this proj- ect. The NDT inspection head is driven by data acquisition software. A three- dimensional schematic of the inspection tools and the vessel wall was entered into the motion control software, which is used to map the path and position of the arm. The data acquisition software is able to plot position coordinates along the cir- cumference of the vessel wall using initial position coordinates previously inputted into the software, enabling it to precisely identify the location of any anomalies indicated by the test data. The robotic arm and attached inspec- \QWV PMIL Å\ \PZW]OP \PM
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on the reactor's upper deck plate and extend ~30 ft down to reach the bottom of the vessel. All system components had
to be constructed of materials approved for insertion into a fueled nuclear reac- tor core and were required to be tested and proven to work in an environment with very high levels of radiation. Ad- ditionally, all of the components needed to be waterproof, because the arm and test equipment will be submerged in heavy water during the inspections. This required some components, such as the electric motors, to be enclosed in _I\MZXZWWN KI[M[ ÅTTML _Q\P QVMZ\ OI[ \W maintain pressure in the event that a leak developed. Four inspection heads that can be
rotated into various orientations were de- signed and built for the NRU's in-service inspections. The heads use either phased array ultrasonic testing (PAUT) or eddy current array testing (ECT) technologies. PAUT, which generates sound waves of short wavelength and high frequency to
The PAUT head on the robotic arm generates sound waves at an ultrasonic frequency selected for this application (5 MHz) to measure material thickness as well as detect flaws. Photo courtesy of Eclipse Scientific.
26 MATERIALS PERFORMANCE March 2012 NACE International, Vol. 51, No. 3