The unit was operating at nominal power. Based on indications from the Burst Can Detection System instrumentaion personnel discovered increased steam activity at the fuel channels (FC) outlet which indicated breach of fuel assembly leak tightness. Once the affected fuel channel with a leaky fuel assembly was identified, efforts were started to extract the fuel assembly from the 47-45 FC. While extracting the fuel assembly radiation monitoring system alarm went off in the central (reactor) hall.
During normal operation at 500 MWe power a blowhole in the flange connection of reactor coolant pump (RCP) and its auxiliary pipeline was discovered. Leak rate did not exceed 6 m3/h. According to operating procedure the unit was shut down using reactor scram button (AZ-5).
Breach of unit safe operation limits and conditions did not occur. Radiation situation in the reactor building and on site was within prescribed limits.
Water leakage was caused by defect in the flange connection between the auxiliary pipeline and the pump casing.