Continuing 137 Cs release to the sea from the Fukushima Dai-ichi Nuclear Power Plant through 2012

The rate of cesium-137 (Cs-137) release to the sea from the Fukushima Dai-ichi Nuclear Power Plant for the period until September 2012 was estimated. Publicly released data on Cs-137 radioactivity in seawater near the power plant by Tokyo Electric Power Company strongly suggest a continuing release of radionuclides to the sea. The plant has an artificial harbour facility, and the exchange rate of harbour water with surrounding seawater was estimated by the decrease in radioactivity immediately after an intense radioactive water release. The estimated exchange rate of water in the harbour was 0.44 d(-1) during the period from 6 to 19 April. The Cs-137 radioactivity in the harbour water was substantially higher than that of seawater outside and remained relatively stable after June 2011. A quasi-steady state was assumed with continuous water exchange, and the average release rate of Cs-137 was estimated to be 93 GBq d(-1) in summer 2011 and 8.1 GBq d(-1) in summer 2012.