Re-suspension of the radioactive fallout after the Fukushima accident: Risk of internal dose during the first week and the first two months

1
Re-suspension of the radioactive fallout after
the Fukushima accident Risk of internal dose
during the first week and the first two months
M. Yamauchi, M. Takeda, M. Makino, T. Owada
(1) Kyoto University, Japan (2) Swedish
Institute of Space Physics (IRF), Kiruna,
Sweden (3) AIST, Tsukuba, Japan (4) Kakioka
Magnetic Observatory, JMA, Ishioka, Japan
2
Total release
1017 Bq for 131,132I 1016 Bq for 134,137Cs
15 of Chernobyl Accident (Estimate by Nuclear
and Industrial Safety Agency, Japan)
3
Three types of fallout
(c)
(b)
(a)
(a)
(b)
(c)
(fallout process is presented at Poster tonight)
4
Measurement methods
multipoint, main feature
supplement
Main feature
weather data (wind, rain, sunshine)
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Overview (PGdose rate) 2 month
PG dropped to zero on 14 and 20 March (Poster)
PG recovery despite enough ionizing radiation
Rain
cf. after Chernobyl
(PG at Helsinki)
Accident
29/4 1/5
10/5
6
PG drop without rain recover _at_ higher dose
rate ? re-suspension until rain settle the
dust to the surface
7
20 March
14 March
Large-scale re-suspension during 16-20 March
8
How about after the rain?
PG dropped to zero on 14 and 20 March (see Poster)
PG recovery despite enough ionizing radiation
Daily variation with peak at local noon
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Re-suspension after rain
(LTUT-9h)
21 March
daily variation ? re-suspension during day
10
Daily variation in the dose rate ???
anti-correlation
from Fukushima to Iitate
Correlate with wind in Iitate but not in
Fukushima-shi ? could be instrumental effect?
(by temperature)
11
Inter-regional transport
Alternating wind direction (diffusive process) ?
Likely from high-dose sites to low-dose sites ?
Ratio of two dose values should approach to
unity
12
Check at large distance
We can assume the same 131I/137Cs ratio ? Ratio
of dose rates approached to unity ? Diffusive
secondary transport
13
But, exception Iitate
Not approaching to unity Episode of departing
from unity ? keep supplied from surroundings ?
from FNPP-1? / from trees?
14
Anomaly events
PG dropped to zero on 14 and 20 March (see Poster)
PG recovery despite enough ionizing radiation
Daily variation with peak at local noon
Reset of recovery and daily variation new
deposition!
15
correlation?
8 April (yes) ? large-scale event 18 April
(no) 26 April (?)
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minor re-suspension (release) from the FNPP-1 ?
3 month after the accident
17
Yes!
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Summary
Combination of different data helps understanding
the motion of the radioactive dust that gives
risk of internal dose. Radioactive dust was
suspended above the ground first two days (14-16
March). Re-suspension was quite significant
until the first rain settled the radioactive dust
to the surface (16-20 March). Until end of
April, dust are re-suspended to move from
highly-contaminated area to moderately-contaminate
d area in average. Occasionally, bulk inflow
events occurred. It might be either large-scale
transport (e.g., from FNPP-1) or local transport
(e.g., from trees). Minor release from the
FNPP-1 (most likely re-suspension) continued for
more than 3 months.
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Vertical Electric field
( potential gradient PG)
Global current 1kA Ionospheric potential200kV
about 100 V/m under clear sky
Rain cloud Ordinary cloud local
generator Thunderstorm global generator Clear
sky Dry air return current inside highly
resistive air
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Ion density n dn/dt q - an2 - ßnN
q production (by cosmic ray, radon, and
?-ray) aneutralization ßattaching to aerosol
(density N)
negative ion
positive ion
?


?
?



?
aerosol
?
?


?
?

?

molecule
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With atmospheric electric (E) field
negative ion
positive ion
?


?
?


E

?
aerosol
?
?


?
?

?

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Atmospheric electric field near ground
Conductivity near the ground is very very low (
10-14/Om)
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2011-3-13 (00 UT)
2011-3-14 (00 UT)
2011-3-15 (00 UT)
2011-3-16 (00 UT)
24
2011-3-17 (00 UT)
2011-3-18 (00 UT)
2011-3-19 (00 UT)
2011-3-20 (00 UT)
2011-3-21 (00 UT)
2011-3-22 (00 UT)
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recovery phase
The night-time background is returning, but this
recovery resets around 8 April, 18 April, 10 May.
gt Rain-forced fallout from trees?
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Chernobyl examples of PG change
? Only one drop with rain
PG at Helsinki after Chernobyl Accident
Rain
26/4 29/4 1/5
10/5
Accident Plume released to north
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cf. Past examples of PG reaction
PG at Tuscon after Navada Test
Shower
Shower
12 16 20
24 4 8
Harris, 1955 (JGR)
Nuclear Tests Wet (hard) /long
distance Chernobyl Wet (hard)/long distance
Dry/short distance Fukushima Wet (soft) Dry /
both gt 100 km
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Map
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Time line (1) Nuclear Plant
Vent
2011-03-11 (06 UT) Earthquake 2011-03-12 (01
UT) Venting (reactor 1) 2011-03-12 (07 UT)
Explosion (reactor 1) 2011-03-13 (00 UT)
Venting (reactor 3) 2011-03-13 (02 UT) Venting
(reactor 2) 2011-03-13 (20 UT) Venting
(reactor 3) 2011-03-14 (02 UT) Explosion
(reactor 3) 2011-03-14 (15 UT) Venting
(reactor 2) 2011-03-14 (21 UT) Explosion
(reactor 2)
high-P building
cooler
reactor
The explosions are by H2 which is leaked from
vent line
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Plume detected by Dosimeter
Passage of radioactive plumes judged by radiation
dose rate