Numerical Modeling of the Releases of 90Sr from Fukushima to the Ocean: An Evaluation of the Source Term

Abstract

A numerical model consisting of a 3D advection/diffusion equation, including uptake/release reactions between water and sediments described in a dynamic way, has been applied to simulate the marine releases of 90Sr from the Fukushima power plant after the March 2011 tsunami. This is a relevant issue since 90Sr releases are still occurring. The model used here had been successfully applied to simulate 137Cs releases. Assuming that the temporal trend of 90Sr releases was the same as for 137Cs during the four months after the accident simulated here, the source term could be evaluated, resulting in a total release of 80 TBq of 90Sr until the end of June, which is in the lower range of previous estimates. Computed vertical profiles of 90Sr in the water column have been compared with measured ones. The 90Sr inventories within the model domain have also been calculated for the water column and for bed sediments. Maximum dissolved inventory (obtained for April 10th, 2011) within the model domain results in about 58 TBq. Inventories in bed sediments are 3 orders of magnitude lower than in the water column due to the low reactivity of this radionuclide. 90Sr/137Cs ratios in the ocean have also been calculated and compared with measured values, showing both spatial and temporal variations.