Refurbishment of Secondary System and High AVT Water Treatment of GENKAI # 1 and # 2

概要

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Kyushu Electric Power Company 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 both feed water iron concentration reduction to around 1 ppb as an indication of the effects and scale adhesion reduction of feed water pumps and feed water heaters.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 both the SG blow down demineralizing and the replacement of copper alloy tube heat exchangers to stainless steel and titan tubes eliminating the copper materials.Further more the scale adhesion mechanism was introduced of the high temperature region of the secondary system based on field examination for iron characterization of both AVT and of HAVT in Genkai units, confirming HAVT advantageous effect for prevention of the scale adhesion.