PURPOSE: To provide a method of controlling the quality of water which enables reduction of the concentration of 6OCO ions even in change of the operational environment in the future, by providing a turbine, a condenser, a purifying device, etc., by using as an index the inventory of CO accumulated on a cladding tube of a fuel rod and by controlling the quality of cooling water inside a reactor toward the reduction of the inventory.
CONSTITUTION: As to a corrosion product brought into a reactor pressure vessel 10, a sample collected through a supply water sampling line 14 is measured by a concentration measuring device 17. A hollow yarn membrane filter of 100% by volume is used for a condensate prefilter 4 so that an iron concentration among measured values be 0.1ppb or below, for instance, and oxygen is injected into supply water on the downstream side of a condensate demineralizer 5 and on the upstream side of a supply water pump 6. Thereby the concentration of dissolved oxygen is controlled to be within the range of 20ppb to 200ppb and thus reduction of the corrosion of a carbon steel piping is enabled. When an iron removal rate of the demineralizer 5 lowers and the iron concentration of the supply water is ready to exceed 0.0ppb, the demineralizer 5 is washed back so as to reduce the inventory of accumulated iron. Thereby the quantity of leaking iron is reduced and the iron concentration is lowered.
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