原因と対策2016� ��5月10日13時00� �.pdf

On January 8, 2016, at 10:45 AM, an alarm signal was triggered at the Ikata Nuclear Power Plant's Unit 3, indicating a temporary increase in the residual chlorine concentration in the discharge pit. The concentration exceeded the standard value of 0.02 ppm for about 20 minutes, with a maximum value of 0.029 ppm. The cause of the increase was attributed to the leakage of sodium hypochlorite from the seawater electrolysis device into the secondary seawater pipeline, which was then discharged into the pit. The leakage was due to a seat leak in the manual valve and check valve, which was caused by the formation of scale on the valve's internal surface. The scale was composed of calcium, which was generated during the seawater electrolysis process. The incident did not have any impact on the plant's operation or the surrounding environment.