The refurbishment of the Lipno I TG2 Francis turbine, situated on River Vltava, with maximum net head of 165 m and required operational range from 0 to 67MW of turbine power was performed in 2014. The new hydraulic design of the spiral case, distributor and runner was developed for this project. After about 1000 hours of operation the site inspection was performed and the cracks were found on 8 runner blades of 17 blades altogether. The all cracks were found near runner hub beginning from the

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... ailing edge. The dimensions of the cracks were different with maximum length of 123 mm and minimum length of 3 mm. The runner was repaired and the intensive investigation was started to define the main cause of the cracks creation and to determine the measures for their elimination. This paper presents the program of this investigation which consists of static and dynamic blade strain measurement, CFD and FEM analysis, discusses the crack causes and overview the solution how to return the turbine successfully to operation.