Fukushima Daiichi Nuclear Power Plant Accident Analysis due to Atmospheric Dispersion

Date 2011-03-25	2011-03-26	2011-03-27
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]

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Conditions

*Table 1 Conditions*
Items	Contents	Reference
Models	Meteorological model：RAMS, Particle transport model：HYPACT	ATMET
Period	March 12th, 2011 - April 7th, 2011
Range	600 km x 600 km with Fukushima Daiichi Nuclear Power Plant in its center
Horizontal lattice	Grid1：600×600[km]、10km mesh
Vertical lattice	σ-z coordinate system, Grid with 20km altitude divided into 30 layers
Radioactive material released	Iodine - 131
Release rate[Bq/s]	Assumption based on released amount estimated by Nuclear Safety Commission*1
Release height	Normal：30m, Explosion：30m-200m	Based on press release
Decay process	Radioactive decay, dry deposition and wet deposition by precipitation
Dry deposition velocity	0.01m/s
Washout parameter α	1.2×10^-4
Washout parameter β	0.8
Number of released particles	ca. 20 million particles
Meteorological data	MSM (Meso Scale Model) isobaric surface data and AMeDAS precipitation*2	Japan Meteorological Agency
Topography data	50m mesh numerical map	Geospatial 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.

Results