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 137Cs released after the Fukushima accident into the Pacific and Indian Oceans. The maximum 137Cs concentration predicted for surface waters of the open NW Pacific Ocean in 2012 (21 Bq/m3 at 38°N, 164°E) will be comparable to that observed during the early 1960s after atmospheric nuclear weapons tests. The 137Cs 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/m3). All the North Pacific Ocean will be labeled with Fukushima 137Cs 10 y after the accident with concentrations below 1 Bq/m3. Thirty years after the accident the 137Cs levels in the Pacific and Indian Oceans will be below 0.1 Bq/m3, 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 134,137Cs. The estimated dose is by about a factor of 500 lower than the present dose limit for the public.