INES Not Applicable
Monitoring instruments (Lines A and B) at the side gutter drainage sounded a “High” alarm at 10:00, followed by an ‘Extremely High’ alarm at 10:10 on 22 February, 2015. Peak values were 5.63 kBq/L at 10:30 for Line A, and 7.23 kBq/L at 10:40 for Line B. The “High” alarm was set at 1.5 kBq/L, and “Extremely High” at 3.0 kBq/L – all the values are for Total Beta.
Multiple drainage gates including one downstream were subsequently closed.
No leakage from tanks was observed, and monitoring posts at the site boundary showed no abnormalities.
Confirming that the radioactivity in the water in the drainage returned to its normal range, the drainage gates were reopened to avoid the risk of water overflowing from the drainage, penetrating soil, and flowing into the ocean in an uncontrollable manner.
The drainage leads to the port which is outside of the controlled area of Fukushima Daiichi NPS. In light of the detection of contaminated water in the drainage, the frequency of monitoring at the drainage and at the port has been intensified .
Event date: Sun, 22-02-2015