Cesium-137 is a beta emitter that was released in huge concentrations from the Fukushima plant.
We will never know the truth about how much was actually released.
Atmospheric and ocean emissions have been continuous since the meltdowns started in Mach of 2011.
Below please find links to a study of oceanic dispersion of Fukushima radiation.
I will have to read the article to know what the authors used for their initial estimations of releases.
Regardless, the dispersion map produced in the study and available here in this video was very disturbing for anyone who lives on or near the Pacific Coast:
Description of the video
*Model simulations on the long-term dispersal of 137Cs released into the Pacific Ocean off Fukushima Published 7/9, 2012. (English explanation) *Erik Behrens et al 2012 Environ. Res. Lett. 7 034004
*GEOMAR | Helmholtz Centre for Ocean Research, Kiel *GEOMAR ヘルムホルツ海洋研究センター、キール http://www.geomar.de/news/article/fukushima-wo-bleibt-das-radioaktive-wasser/
Behrens, E., F.U. Schwarzkopf, J.F. Lübbecke and C.W. Böning, 2012: Model simulations on the long-term dispersal of 137Cs released into the Pacific Ocean off Fukushima. Environmental Research Letters, 7, http://dx.doi.org/10.1088/1748-9326/7/3/034004
hat tip: CB at Enenews