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.