movements of radioactive materials that was released by the fukushima nuclear accident m. yamauchi...
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Movements of radioactive materials that was released by the
Fukushima Nuclear Accident
M. Yamauchi
Total release:
1017 Bq for 131I & 1016 Bq for 137Cs
~ 15% of Chernobyl Accident(Estimate by Nuclear and Industrial Safety Agency, Japan)
Three types of fallouts
Motivation
“Spread” and “dynamics” of the nuclear product is geophysics problem.
We are experts of estimating particle motion from multipoint measurements.
This is a new research field (first time dense-network observation).
Urgently needed because of internal dose problem.
Strong demand from general public “Why do scientists not help?”
Takeda, Yamauchi, Makino, and Owada (2011): Initial effect of the Fukushima accident on atmospheric electricity, Geophys. Res. Lett., 38, L15811, doi:10.1029/2011GL048511.
Yamauchi, M., Takeda, M., Makino, M., Owada, T., and Miyagi, I. (2012): Settlement process of radioactive dust to the ground inferred from the atmospheric electric field measurement, Ann. Geophys., 30, 49-56, doi:10.5194/angeo-30-49-2012.
Yamauchi, M. (2012): Secondary wind transport of radioactive materials after the Fukushima accident, Earth Planets Space, 64(1), e1-e4, doi:10.5047/eps.2012.01.002.
Measurement methods
q: production (by cosmic ray, radon, and -ray)α: neutralizationβ: attaching to aerosol (density N)
Ion density n: dn/dt = q - αn2 - βnN
aerosol
+
positive ion+
+
++
+
+
++
negative ion
molecule
aerosol
With atmospheric electric (E) field
+
+
+
++
+
+
++
negative ion positive ion
E
Vertical Electric field (= potential gradient: PG)
= about 100 V/m under clear sky
Rain cloud: Ordinary cloud = dipole electric field (local generator)Thunderstorm = strong dipole electric field (global generator)
Clear sky:Dry air = electrostatic problems
Global current: 1kAIonospheric potential:200kV
Atmospheric electric field near ground
Conductivity near the ground is very very low (~ 10-14/Ωm)
Effect of the propagation
cf. After Nuclear Test
PG (=vertical E-field)
conductivity (by + ions)
Shower
conductivity (by - ions)
Harris, 1955 (JGR)
12 16 20 24 4 8
cf. Conductivity after Chernobyl
Tuomi, 1988 (Geophysica)
Nuclear Tests = Wet (hard)Chernobyl = Wet (hard)/long distance + Dry/short distanceFukushima = Wet (soft) + Dry / both > 100 km
Ionosphere
Earth
EE
E’
radioactive dust cloud
Nion
Vi
σ =2eNion μion
Ionosphere
Earth
EE
E’
Nion
Vi
σ =2eNion μion
radioactive contamination
effect of global fallout of radioactive dust (nuclear test)
Pierce, 1972 (JGR)
extra dry contamination downstream of Windscale
= downstream
Pierce, 1959 (Pure and Applied Geophysics)Pierce, 1972 (JGR)
different contaminationsdry (by wind) contamination
wet (by rain) contamination
subsurface migration
transport surface wind high-altitude
fallout soft touch on the ground/leaf
hard press to the ground/leaf
chemical bind to soil
resuspension
easy to float and blown off
difficult to float no float
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)
Time line (1): Nuclear PlantVent
reactor
cooler
high-P building
The explosions are by H2 which is leaked from vent line
Time line (2): Release of Radionuclide
0.01
0.1
1
10
100
11 12 13 14 15 16 17 18 19 20 21 22 23
Shirakawa Fukushima MinamiSoma Iwaki Iitate
Massive release even after large evens at the nuclear site until 21 March when first heavy rain fall at the nuclear site.
Time line (3): Vertical E-field (PG)
Six periods of different contamination conditions1. dry contamination, 2. blow away 3. floating, 4. wet contamination5. minor re-suspension 6. recovery
Main Sub
Electrometer Electrostatic sensor type
Field mill type
Collector
Type Water-dropper Mechanical
Height 2.55 m 1.00m
Separation from the wall
1.17 m
Sampling 1 sec 1sec
Latitude Longitude
3613'56"N 14011'11"E
PG measurement at Kakioka
Map
2011-3-13 (00 UT) 2011-3-14 (00 UT)
2011-3-15 (00 UT) 2011-3-16 (00 UT)
Behavior: 3 days
dry contaminationsdry contamination by wind
wet contamination by rain
subsurface migration
fallout soft touch on the ground/leaf
hard press to the ground/leaf
chemical bind to soil
re-suspension
easy to float and blown off
difficult to float no float
dry contamination phase
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)
wet contamination phase
wet contaminationsdry contamination by wind
wet contamination by rain
subsurface migration
fallout soft touch on the ground/leaf
hard press to the ground/leaf
chemical bind to soil
re-suspension
easy to float and blown off
difficult to float no float
Israël, 1973
daily variation (LT=UT-9h)
cf. 2000-2009 statistics (quiet days)
sub-surface migrationdry contamination by wind
wet contamination by rain
subsurface migration
fallout soft touch on the ground/leaf
hard press to the ground/leaf
chemical bind to soil
re-suspension
easy to float and blown off
difficult to float no float
recovery phase
The night-time background is returning, but this recovery resets around 8 April, 18 April, 10 May. => Rain-forced fallout from trees?
due to new fallout from trees?
Is it really no re-suspension?
Alternating wind direction Similar to diffusion process Secondary transport from high-dose sites to low-dose sites ratio approaches unity
systematic check
Obvious candidate for different decay
Different I/Cs ratios (different physical decay) in different regions.
because
half-life is 8 days for I & 2~30 years for Cs
11.21.41.61.82
2.22.42.62.83
0 10 20 30 40 50
C1=60 & C2=20
20 & 88 & 3
8 & 2
3 & 2
days
rati
o of
dos
e
dose rate C*exp(-t/TI) + (-t/TCs): TI=8 days, TCs>2 years, C=I/Cs ratio at t=0
ratio of dose [C1 + exp(+t/T)]/[C2 + exp(+t/T)] : T≈8 days
approach unity,
but with exceptions
(1) Takahagi= I/Cs ratio
(2) Iitate= slow decay
Interpretation for Takahagi
Why is Iitate special?
Wind transport (extra inflow)?If so, what is the transport distance?
Extra weathering loss afterward?
Can wind cause daily variation?
Summary
Networks of Radiation dose measurement & Atmospheric electric field (PG) measurement help understanding the motion of the radioactive dust.
First time to detect the moment of dry contamination (this is impossible without PG measurement).
Re-suspension and secondary transport are significant until end of April, i.e., 50 days after the accident. This give duration of risk for the internal dose through breathing.
It is not too late to put portable electric field instrument (e.g., field mill) after any nuclear accident because it is useful for more than one month.