The unit was operating at nominal power. While performing scheduled refueling (replacement) of a spent fuel assembly (FA) in the 41-40 fuel channel FA separation from the connecting bar occurred, which is a deviation from the normal refueling process. In accordance with the technical specification the unit was scrammed by emergency protection system button. The 41-40 returned to its usual location. Radiation situation in the central hall, sanitary-protective zone and in the supervision area remained unchanged. Breach of unit limiting conditions for operation was not observed. After the reactor was brought to cold shutdown the FA in question was transferred to the spent fuel pool. The 41-40 fuel channel was sealed with a plug in the defueled condition. During the coming preventive maintenance outage detailed inspection of the fuel channel and of the affected FA will be undertaken.