Long-term simulations of the 137Cs dispersion from the Fukushima accident in the world ocean.

The LAMER calculation code was used for simulation of the distribution of (137)Cs released after the Fukushima accident into the Pacific and Indian Oceans. The maximum (137)Cs concentration predicted for surface waters of the open NW Pacific Ocean in 2012 (21 Bq/m(3) at 38 °N, 164 °E) will be comparable to that observed during the early 1960s after atmospheric nuclear weapons tests. The (137)Cs in surface waters of the Pacific Ocean will reach the US coast 4-5 y after the accident, however, the levels will be low (<3 Bq/m(3)). All the North Pacific Ocean will be labeled with Fukushima (137)Cs 10 y after the accident with concentrations below 1 Bq/m(3). Thirty years after the accident the (137)Cs levels in the Pacific and Indian Oceans will be below 0.1 Bq/m(3), i.e. undetectable on the present global fallout background. The effective dose commitment with ingestion of marine biota found in 2012 in the open NW Pacific Ocean was estimated to be 1.7 μSv/y, mostly delivered by (134,137)Cs. The estimated dose is by about a factor of 500 lower than the present dose limit for the public.