Chemistry of the secondary circuit of a WWER 440 MW nuclear power plant

The steam generator chemistry is affected by the presence of salts, corrosion products and other compounds in the secondary circuit. Impurities get deposited and corrosion active salts concentrate on heat exchange surfaces. The mean value of the annual deposit increment for steam generators of Czechoslovak nuclear power plants is 5.2-10.7 g.m-2. The deposit consists of up to 90% iron oxides, and to a lesser extent of silicon dioxide, and calcium and magnesium salts. 3-5% of corrosion products are surface blowdown. In order to improve steam generator reliability, it is recommended to revise the chemistry standards of feedwater, of boiler water, steam and condensate; to increase the amount of continuous surface blowdown to at least 1% and to optimize the point of its removal; to check the moisture content of outgoing steam; to develop suitable procedures of steam generator preservation during shutdowns; and to improve chemistry inspections. (M.D.)