Water quality control method and device in BWR type reactor primary coolant system

A specimen is sampled through a sampling line disposed to the upstream of a reactor cleanup device, to measure the concentration of iron and copper in a reactor water by using a concentration measuring device. Then, the ratio of Fe/Cu concentration is calculated based on the concentration of iron and copper in the measured reactor water. If the value is smaller than 2, the ratio of Fe/Cu concentration in the reactor water is controlled to greater than 2 by increasing the amount of iron in feedwater injected from an iron forming device to the side of the exit of an condensator desalter. With such procedures, copper deposited on the surface of fuel rods can be fixed to a stable chemical form of ferrite oxide. Accordingly, since the valence of Cu ions in fuel rod deposits can be kept identical with that of the valence of Cu ions in reactor water, accelerated corrosion of zirconium, as the main constituent element of the fuel cladding tube, can be prevented. With such procedures, integrity of the fuel cladding tube can be maintained throughout the use of the fuel. (I.N.)