Primary water chemistry control at units of Paks Nuclear Power Plant

The primary water chemistry of the four identical units of Paks Nuclear Power Plant has been developed based on Western-type PWR units, taking into consideration some Soviet-Russian modifications. The political changes in 90s have also influenced the water chemistry specifications and directions. At PWR units the transition operational modes have been developed while in case of VVER units - in lack of central uniform regulation - this question has become the competence and responsibility of each individual plant. This problem has resulted in separate water chemistry developments with a considerable time delay. The needs for life-time extensions all over the World have made the development of start-up and shut-down chemistry procedures extremely important, since they considerably influence the long term and safe operation of plants. The uniformly structured limit value system, the principles applied for the system development, and the logic schemes for actions to be taken are discussed in the paper, both for normal operation and transition modes. (author)