Some water-chemical aspects of variable operation modes of WWER NPP

The presented review of literature consider both contradicting points of view about the necessity of periodical power changes in NPP: 1) the probability of accident is increasing due to water activity changes and hence the NPP should maintain the longest possible operation in a stable regime: 2) the power alterations are necessary as a radical tool against the corrosion denting of steam generators caused by hideout phenomena. Special attention is paid to the ways of reduction of corrosion products during the temporary transient operation modes, when the unit power is decreasing without reaching zero values. It is stated as a conclusion that in the transient operation modes suitable water-chemical conditions could be found allowing the operation of the primary and secondary coolant circuits to be performed without any negative consequences. 9 refs, 6 figs