[en] The corroded condition of four assembly channels was investigated after various service times. The inner surface of three of them in contact with the aqueous heat carrier was subjected to local nodule corrosion, the depth of which depends upon the neutron fluence. Within the scope of the electrochemical mechanism of the corrosion process an expression for the predicted thickness of the corrosion film of a nodule and an equation for calculation of the error are proposed. The linear regression method also provides close results in prediction for 20 years of service