Modeling of 137Cs as a Tracer in a Regional Model for the Western Pacific, after the Fukushima-Daiichi Nuclear Power Plant Accident of March 2011

In this study, results are presented from the first operational ocean tracer dispersion model operated by the National Oceanic and Atmospheric Administration/National Weather Service/National Centers for Environmental Prediction (NOAA/NWS/NCEP). This study addresses the dispersion of radionuclide contaminants after the Fukushima-Daiichi nuclear accident that was triggered by the 11 March 2011 earthquake and tsunami. The tracer capabilities of the Hybrid Coordinate Ocean Model (HYCOM) were used in a regional domain for the northwestern Pacific, with nesting lateral boundary conditions using daily nowcast-forecast fields from the global operational Real-Time Ocean Forecast System (RTOFS-Global), a 1/12 degrees HYCOM global forecast from NCEP, based on data-assimilative 1/12 degrees HYCOM Global Ocean Forecast System (GOFS) analyses from the Naval Research Laboratory/Naval Oceanographic Office (NRL/NAVOCEANO). This regional model, RTOFS Episodic Tracers for a region of the North West Pacific (RTOFS-ET_WPA), was in operation until the beginning of 2014, when the simulated Cs-137 concentration was very close to the background level in the Pacific before the accident, which was about 2 Becquerel m(-3) [Bq; 1 Becquerel = 1 (nuclear decay) s(-1)].