Water quality control method and device

An ion exchanger in the form of a metal ion is disposed in a reactor water cleanup device as a portion or the entire of an adsorbent, and purified water is passed therethrough to control the concentration of metal ions in the reactor water to a predetermined value utilizing an ion exchange equilibrium. Namely, an ion exchanger in the form of an aimed metal ion is used as a reactor water cleanup device. If purified water is flown to a cation exchanger which is formed into a metal ion previously, a predetermined amount of salts can be flown out and charged into the reactor by utilizing the equilibrium of the concentration between metal ions and that of H ions. Then, a slight amount of useful metal ions, for example, Ni2+ and Zn2+ are involved during formation of oxide membrane of pipelines and formed into a strong membrane, and deposition of radioactive metal ions such as Co-60 is suppressed to provide an effect of reducing radiation exposure. The concentration of metal elements such as nickel and zinc which tends to be adsorbed to ion exchange resins can be controlled effectively. (N.H.)