Deaerating operation during startup periods in Japanese BWRs

The IGSCC has been mitigated by application of effective countermeasures on water chemistry environment. Hydrogen water chemistry (HWC) has been implemented to reduce the reactor water dissolved oxygen concentration and electrochemical corrosion potential (ECP) during plant operation to reduced crack growth rate of in sensitized stainless steel. But the HWC has not been implemented during startup periods. The crack growth rate of sensitized stainless steel will increase obviously during startup period by increasing in temperature under high dissolved oxygen conditions [1]. The deaerating operation has been applied routinely in Japanese BWRs to reduce reactor water dissolved oxygen quickly and easily before plant startup [2,3]. The main condenser is vacuumed up before start in the deaerating operation. The reactor is connected with the main condenser by opening the main steam bypass valves or the main steam drain valves. The deaerating operation is started with keeping the reactor water temperature about 70 to 90 degrees centigrade. The deaerating operation will come to an end when the reactor water dissolved concentration will decrease below 200 ppb. This paper shows the procedure and actual results of deaerating operation. (authors)