CHEMICAL DECONTAMINATION METHOD

To grasp a state of removing carbonic acid in treatment water with high accuracy.SOLUTION: A chemical decontamination method is a chemical decontamination method for performing chemical decontamination with treatment water including carbonic acid for a system of a nuclear power plant having a member including a nickel-based alloy. The method has a step for reducing the carbonic acid in the treatment water held in a tank. The step for reducing the carbonic acid includes the steps of: acquiring a target addition amount which is an addition amount of a hydroxide of an alkali metal necessary for making the treatment water in the tank into treatment water of target pH which is pH being a target; acquiring the target addition amount for the treatment water in the tank again after a lapse of fixed time after the acquisition of the target addition amount; and determining whether or not a difference between the target addition amount acquired again and the target addition amount acquired before the lapse of fixed time with respect to the step of acquiring the target addition amount again is lower than a predetermined reference value.SELECTED DRAWING: Figure 3 【課題】処理水中の炭酸の除去状況を高い精度で把握する。【解決手段】化学除染方法は、ニッケル基合金を含む部材を有する原子力プラントの系統に対して、炭酸を含む処理水によって化学除染を行う化学除染方法であって、前記処理水をタンクに保持された前記処理水中の炭酸を低減する工程を有し、前記炭酸を低減する工程は、前記タンク中の前記処理水を目標とするｐＨである目標ｐＨとするために必要なアルカリ金属の水酸化物の添加量である目標添加量を取得する工程と、前記目標添加量を取得して一定の時間が経過した後に、前記タンク中の前記処理水に対する目標添加量を再度取得する工程と、再度取得された前記目標添加量と、前記目標添加量を再度取得する工程に対して前記一定の時間経過前に取得された前記目標添加量との差分が予め定めた基準値を下回っているか否かを判定する工程とを含む。【選択図】図３