Fukushima Daiichi Nuclear Power Plant Accident Analysis due to Atmospheric Dispersion

Date 2011-04-03 2011-04-04 2011-04-05
Hour 23 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00

Ground level air concentration [Bq/m3]
2011-04-04 21< 2011-04-04 22 >2011-04-04 23
Ground level air concentration [Bq/m3] 2011-04-04 22
2011-04-04 21< 2011-04-04 22 >2011-04-04 23


Table 1 Conditions
ModelsMeteorological model:RAMS, Particle transport model:HYPACTATMET
PeriodMarch 12th, 2011 - April 7th, 2011
Range600 km x 600 km with Fukushima Daiichi Nuclear Power Plant in its center
Horizontal latticeGrid1:600×600[km]、10km mesh
Vertical latticeσ-z coordinate system, Grid with 20km altitude divided into 30 layers
Radioactive material releasedIodine - 131
Release rate[Bq/s]Assumption based on released amount estimated by Nuclear Safety Commission*1
Release heightNormal:30m, Explosion:30m-200mBased on press release
Decay processRadioactive decay, dry deposition and wet deposition by precipitation
Dry deposition velocity0.01m/s
Washout parameter α1.2×10-4
Washout parameter β0.8
Number of released particlesca. 20 million particles
Meteorological dataMSM (Meso Scale Model) isobaric surface data and AMeDAS precipitation*2Japan Meteorological Agency
Topography data50m mesh numerical mapGeospatial Information Authority of Japan

*1 At this point of time, accurate release amount is still unknown. We estimated the release ratio by multiplying coefficient and dose rate at main gate of the facility.(Fig.2)
*2 Precipitation map made from AMeDAS data was derived and applied because precipitation data produced by a meteorological model was not sufficient.

These simulations are based on publicly available data and original assumptions. Audience should be aware that accuracy of calculation is limited. We would appreciate audience matter-of-factly comprehend our results. We frequently update the calculation whenever additional information is obtained.


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