Monitoring of BWR water chemistry and oxide films on samples at Olkiluoto 1 during the fuel cycle 2000-2001

A flow-through cell unit has been installed in the shutdown cooling system 321 at Olkiluoto 1 in May 2000 in order to collect the data needed for establishing the correlations between rate of activity incorporation, water chemistry data and the properties of oxide films formed on material samples. Observations and correlations related to susceptibility to stress corrosion cracking and other forms of corrosion are also looked for. The monitoring unit provides relevant hightemperature water chemistry information that can be well used both for assessing long-term trends and for sensitive detection of rapid changes in the coolant environment. Also the material sample cell has been verified to give a representative view of activity incorporation and oxidation of construction materials in the primary coolant. The results have indicated marked differences between the behaviour of different isotopes and different materials. It has become evident that he thickness of the oxide film is not the only factor that correlates with the extent of activity build-up. (orig.)