Estimation of particulate and dissolved Cs discharge from rivers to the ocean near the Fukushima Dai-ichi Nuclear Power Plant using a simple model

Sakuma, Kazuyuki   ; Aoyama, Michio*; Nakanishi, Takahiro   ; Kurikami, Hiroshi  ; Machida, Masahiko  ; Yamada, Susumu  ; Iwata, Ayako

MERCURY is one of the models developed to simply predict Cs discharge from rivers to the ocean for understanding of Cs migration from seawater and sediment to the ecosystem and for estimating Cs discharge under heavy rainfall immediately. It is composed of a tank model, relationships between water discharge and suspended solids load, and two-component exponential models for river water Cs concentration. Using the MERCURY, Cs discharge to the ocean from five rivers near the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in 2018 and 2019 was estimated to be 0.23 and 0.81 TBq. Cs discharge in 2019 was larger than in 2018 due to the two huge typhoons in October 2019, Hagibis and Bualoi. Although the model has some limitations such as underestimating the Cs discharge during a heavy rainfall due to lack of modeling dependence of Cs concentration on sediment size, it can quickly evaluate the effect of Cs discharge from rivers to the coastal area near FDNPP.