Observation of fallout deposition in an outdoor swimming pool 50 km away from the Fukushima Daiichi Nuclear Power Plant

Saegusa, Jun; Yasuda, Ryo; Kurikami, Hiroshi  

After the Fukushima Daiichi Nuclear Power Plant (NPP) accident, the fallout deposited in an outdoor swimming pool was observed. At a pool situated 50 km away from the NPP, the average concentrations of radiocesium for the water and sediment were quantified as 170 Bq L and 3.610 Bq kg, respectively. Taking account of these concentrations and of the water balance in and around the pool, the deposition density of radiocesium, as of August 2011, was precisely estimated to be 0.320.03 MBq m ( = 1). The density corroborated the previous results obtained by the other methods, i.e., airborne surveys, in-situ Ge surveys and soil samplings at neighboring locations. The radioactivity concentrations of Sr, Sr, Pu and Pu in the water were all less than the minimum detectable activities - 2, 0.1, 0.002 and 0.002 Bq L, respectively.