Atmospheric radiation was detected on the U.S. West Coast within days of the incident, but radioactive particles in the ocean plume take considerably longer to travel the same distance.
Writing in the journal Deep-Sea Research 1, scientists with the Australian Research Council's Center of Excellence for Climate System Science said it is likely to be harmless when it arrives.
"Observers on the West Coast of the United States will be able to see a measurable increase in radioactive material three years after the event," researcher Erik van Sebille said in an ARC release Wednesday.
"However, people on those coastlines should not be concerned as the concentration of radioactive material quickly drops below World Health Organization safety levels as soon as it leaves Japanese waters."
Two energetic currents off the Japanese coast -- the Kuroshio Current and the Kurushio Extension -- are primarily responsible for accelerating the dilution of the radioactive material to safe levels, the researchers said.
Other currents in the open ocean will contribute to this dilution process and direct the radioactive particles to different areas along the U.S. West Coast, they said.
"Although some uncertainties remain around the total amount released and the likely concentrations that would be observed, we have shown unambiguously that the contact with the north-west American coasts will not be identical everywhere," researcher Vincent Rossi said.