Civil Engineering Reference
In-Depth Information
model, WRF,
3
in a way that it generated JRodos-usable local meteorological fields
for Japan on the basis of global prognostic and re-analysis meteorological predic-
tion data publically available from the American NOMAD server.
4
Since March
17, 2011, the meteorological data field generation became operational and was used
for carrying out prognostic calculations with JRodos for different points in time.
The third step consisted in obtaining radiological source terms from the German
Gesellschaft f
¨
r Reaktorsicherheit
5
(GRS) and integrating them into JRodos. In all,
GRS provided two source terms, one for a release from a few destroyed fuel
elements (“gap release”) and one for a core melt scenario, respectively.
The IKET Accident Consequence Group used the upgraded JRodos system for
performing own dose assessments for potential releases from the Fukushima-
Daiichi nuclear power plant. Only the first 300 km around the site were taken
into account because emergency measures are limited to the vicinity of a site. The
first assessments were devoted mainly to find out whether Tokyo was endangered
and up to which distance from the facility a potential for emergency measures
existed. Both questions were covered by calculations using the above-mentioned
GRS source terms or in-house source term assumptions and a number of weather
variations. The only reference values available consisted of dose rate measurements
close to the facility that were provided by GRS and placed on publically accessible
web pages.
6
By middle/end of the first week local dose rates measurements (in micro-Sievert/
h) for more locations became published. This allowed for the first time at least a
rough estimate of the releases from the reactors and from the spent fuel storage
pool. The source term estimated in this way was clearly higher than the GRS fuel
element source term, but still considerably below the GRS core melt source term,
indicating a release of a few parts per million of the initial core inventory of
Fukushima-Daiichi Unit 2.
The measurements had shown that the source term was dominated by iodine and
cesium,
7
and further estimates concentrated on these two radionuclides. Moreover,
the releases decreased markedly after March 17, thus putting the emphasis on
recalculations of the prior release period. Assuming a release of roughly
1.0
10
16
Bq over four days (March 12, 2011-March 16, 2011) the re-analysis
data of the meteorological WRF model were used to estimate the soil contamination
by cesium 137 (Fig.
22.1
).
The values calculated are comparable with data measured by U.S. and Japanese
institutions published under
http://energy.gov/articles/us-department-energy-
releases-radiation-monitoring-data-fukushima-area
, cf. Fig.
22.2
.
3
WRF stands for Weather Research and Forecasting, cf.
http://www.wrf-model.org/index.php
4
Data from the Global Forecast Systems (GFS), cf.
http://www.emc.ncep.noaa.gov/FGS/
