One of the ageing phenomena of pressure boundary components of light water reactors is environmentally- assisted cracking. The project CASTOC (5th framework programme of the EC) was launched in September 2000 with six European partners and terminated in August 2003. It focused in particular on the crack growth behavior of low-alloy steels and to some extent to weld metal, heat affected zone and the influence of an austenitic cladding. The main objective was directed to a more detailed understanding of the acting mechanisms and to generate data on crack growth rates under complex loading conditions to simulate transients in load and in water chemistry which may occur during operation or start-up/shut-down of a plant. Autoclave tests were performed with Western and Russian type reactor pressure vessel (RPV) steels under simulated boiling water reactor (BWR)/normal water chemistry (NWC) and pressurized water reactor (VVER) conditions. The investigations were performed with fracture mechanics specimens of different size and geometries. The applied loading comprised cyclic loads, static loads and load spectra where the static load was periodically interrupted by partial unloading. With regard to water chemistry, the oxygen content (VVER) and impurities of sulphate and chlorides (BWR) were varied beyond allowable limits for continuous operation. The current paper summarizes the most important crack growth results obtained under simulated VVER conditions. The influence of oxygen content and the effect of specimen size (CT25 versus CT50 specimens) on the crack growth rates are shown. The results are discussed in the context of the current crack growth rate curves in the corresponding nuclear codes.