5 research outputs found
Appearances of Fukushima Daiichi Nuclear Power Plant-Derived <sup>137</sup>Cs in Coastal Waters around Japan: Results from Marine Monitoring off Nuclear Power Plants and Facilities, 1983–2016
Monitoring
of <sup>137</sup>Cs in seawater in coastal areas around
Japan between 1983 and 2016 yielded new insights into the sources
and transport of Fukushima Daiichi Nuclear Power Plant (FDNPP)-derived <sup>137</sup>Cs, particularly along the west coast of Japan. Before the
FDNPP accident (1983–2010), the activity concentrations of <sup>137</sup>Cs, mainly from fallout, were decreasing exponentially.
Effective <sup>137</sup>Cs half-lives in surface seawater ranged from
15.6 to 18.4 yr. After the FDNPP accident (March 2011) <sup>137</sup>Cs activity concentrations in seawater off Fukushima and neighboring
prefectures immediately increased. Since May/June 2011, <sup>137</sup>Cs activity concentrations there have been declining, and they are
now approaching preaccident levels. Along the west coast of Japan
remote from FDNPP (i.e., the Japan Sea), however, radiocesium activity
concentrations started increasing by 2013, with earlier (May/June
2011) increases at some sites due to airborne transport and fallout.
The inventory of <sup>137</sup>Cs in the Japan Sea (in the main body
of the Tsushima Warm Current) in 2016 was calculated to be 0.97 ×
10<sup>14</sup> Bq, meaning that 0.44 × 10<sup>14</sup> Bq of
FDNPP-derived <sup>137</sup>Cs was added to the estimated global fallout <sup>137</sup>Cs inventory in 2016 (0.53 × 10<sup>14</sup> Bq). The
net increase of <sup>137</sup>Cs inventory in the Japan Sea through
the addition of FDNPP-derived <sup>137</sup>Cs accounts for approximately
0.2% of the total <sup>137</sup>Cs flux from the plant to the ocean
from the accident
Appearances of Fukushima Daiichi Nuclear Power Plant-Derived <sup>137</sup>Cs in Coastal Waters around Japan: Results from Marine Monitoring off Nuclear Power Plants and Facilities, 1983–2016
Monitoring
of <sup>137</sup>Cs in seawater in coastal areas around
Japan between 1983 and 2016 yielded new insights into the sources
and transport of Fukushima Daiichi Nuclear Power Plant (FDNPP)-derived <sup>137</sup>Cs, particularly along the west coast of Japan. Before the
FDNPP accident (1983–2010), the activity concentrations of <sup>137</sup>Cs, mainly from fallout, were decreasing exponentially.
Effective <sup>137</sup>Cs half-lives in surface seawater ranged from
15.6 to 18.4 yr. After the FDNPP accident (March 2011) <sup>137</sup>Cs activity concentrations in seawater off Fukushima and neighboring
prefectures immediately increased. Since May/June 2011, <sup>137</sup>Cs activity concentrations there have been declining, and they are
now approaching preaccident levels. Along the west coast of Japan
remote from FDNPP (i.e., the Japan Sea), however, radiocesium activity
concentrations started increasing by 2013, with earlier (May/June
2011) increases at some sites due to airborne transport and fallout.
The inventory of <sup>137</sup>Cs in the Japan Sea (in the main body
of the Tsushima Warm Current) in 2016 was calculated to be 0.97 ×
10<sup>14</sup> Bq, meaning that 0.44 × 10<sup>14</sup> Bq of
FDNPP-derived <sup>137</sup>Cs was added to the estimated global fallout <sup>137</sup>Cs inventory in 2016 (0.53 × 10<sup>14</sup> Bq). The
net increase of <sup>137</sup>Cs inventory in the Japan Sea through
the addition of FDNPP-derived <sup>137</sup>Cs accounts for approximately
0.2% of the total <sup>137</sup>Cs flux from the plant to the ocean
from the accident
The Contribution of Sources to the Sustained Elevated Inventory of <sup>137</sup>Cs in Offshore Waters East of Japan after the Fukushima Dai-ichi Nuclear Power Station Accident
We have evaluated
the contribution of sources of <sup>137</sup>Cs to the inventory of
radiocesium in waters (surface area: 6160
km<sup>2</sup>, water volume: 753 km<sup>3</sup>) off Fukushima Prefecture
and neighboring prefectures from May 2011 to February 2015. A time-series
of the inventory of <sup>137</sup>Cs in the offshore waters revealed
a clearly decreasing trend from May 2011 (283.4 TBq) to February 2015
(1.89 TBq). The <sup>137</sup>Cs inventory about four years after
the accident was approximately twice the background inventory of 1.1
TBq. The magnitudes of the <sup>137</sup>Cs influxes from sources
into offshore waters for periods of 182–183 days were estimated
from the first period (1 October 2011 to 31 March 2012: 15.3 TBq)
to the last period (1 October 2014 to 31 March 2015: 0.41 TBq). We
assumed that three sources contributed <sup>137</sup>Cs: continuous
direct discharge from the Fukushima Dai-ichi Nuclear Power Station
(FNPS) even after the massive discharge in late March 2011, desorption/dissolution
from sediments, and fluvial input. Quantification of these sources
indicated that the direct discharge from the FNPS is the principal
source of <sup>137</sup>Cs to maintain the relatively high inventory
in the offshore area