Kyushu electric co. Genkai #1 and #2 are twin 500 Mw class first generation PWR power stations starting their commercial operation in 1975–1981. The units were recently altered their secondary water treatment from AVT to HAVT (High All Volatile Treatment) operation aiming to suppress erosion in piping and equipment, resulting in feed water iron concentration reduction to around 1 ppb as indication of the effects. The units had been successfully operated from the start of their commercial operation except for scale adhesion to SG and others, degradation of copper alloy material tubes in auxiliary heat exchangers and lower condenser vacuum derived from protective ferrous sulfate coating. Life cycle management program was implemented resulting in the alteration of water treatment to HAVT adopting the SG blow down demineralizing and the replacement of copper alloy tube heat exchangers to stainless steel and titan tubes. Further more the examination results were introduced, of the scale adhesion mechanism in the high temperature region of the secondary system based on actual plants iron characterization data and field examination results of HAVT of Genkai units, expecting HAVT application would be effective for the scale adhesion reduction.

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