[en] The increase of the pH of SG feedwater on the 1. unit of Dukovany NPP led to enhancement of chemical mode of secondary circuit, what was identified in particular by the following: Reduction of concentration of iron in SG feedwater, Reduction of concentration of Sodium and Sulfates in SG blowdown water. This reduction is caused by shutdown of CPS thus by elimination of release of Na ions and SO₄ from wrong operated ion-exchangers and their subsequent regeneration (part of cation exchanger in Na form and part of anion exchanger in SO₄ form). Reduction of the WANO SG chemical index to the minimum theoretical value. It will be necessary to change criteria characterizing this index or to introduce our own modified index. In relation to CPS shutdown the costs for operating chemicals and for demineralized flushing water were reduced. (authors)