Lifting the control rod sleeves (CRS) is one of the initial steps of the refuelling of the VVER-400-213 type reactor, which are operating at Paks NPP. If any fuel-cassette adheres to the CRS during its lift, it can result in unplanned exposure of the workers. The monitoring system has been recalibrated, because the first calibration of the monitoring system had been implemented 20 years ago, and Paks NPP had changed the fuel cycle from 12 months to 15 months. The task was performed under the refuelling outage of unit 1 in 2018. During preparatory works performed for refuelling of the same unit, at 6th May 2021 the monitoring system indicated the adhesion of the one of the fuel cassettes to the CRS. This work provides an overview about the operation of the system, about completed tasks relating to recalibration of the measuring system and about the adhesion event on the unit 1.
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