Fuel deposits and water chemistry at TVO I power station during the first three fuel cycles

TVO 1 is a 660 MWe direct-cycle, light-water cooled BWR of Asea-Atom design. The unit has just completed the 4th cycle. Sampling of deposits on fuel surfaces has been performed by Asea-Atom after each cycle. The deposits consist mainly of iron (78-86%) excepting two rods in a bundle belonging to the first reload. On these two rods the amounts of Cr and Cu were exceptionally high indicating differences in the deposition processes between the initial fuel and the first reload. In general the crud thickness is highest at a height of 1 to 1.5 meters from the bottom plate of the bundle. The average concentrations of the corrosion products vary from 3.6 to 10.3 g/m2/bundle. Inexplicable large variations of the crud amount between the bundles and between the individual rods in a bundle have been measured. Growth rate of deposits is decreased and water chemistry is improved with improved operation of the plant. During normal operation many impurities are below the detection limit thus making the interpretation of the results difficult. (author)