[en] As part of the IRR2 reactor preventive maintenance, an ultrasonic scanning system was developed for inspection of the reactor tank wall. The design validation was carried out in a full-sized mock-up. An important issue tested in the mock-up experiments was the ultrasonic scanning system sensitivity to electromagnetic noise. Indeed, the system was approved only after the noise levels were found to be tolerable. However, when the Ultrasonic Inspection System was first operated in the IRR2 reactor, unacceptable noise levels were measured, i. e., system immunity to electromagnetic noise demonstrated in the mock-up testing proved to be irrelevant for the IRR2 reactor itself Various methods of noise reduction were attempted; consequently, noise interference was reduced to an acceptable level