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

10 17 Bq for 131,132 I & Bq for 134,137 Cs ~ 15% of Chernobyl Accident (Estimate by Nuclear and Industrial Safety Agency, Japan) Total release

(fallout process is presented at Poster tonight) (a) (b) (c) Three types of fallout (a)(b)(c)

Measurement methods multipoint, main feature supplement Main feature + weather data (wind, rain, sunshine)

Overview (PG+dose rate): 2 month PG dropped to zero on 14 and 20 March (Poster) PG recovery despite enough ionizing radiation cf. after Chernobyl 29/4 1/5 10/5 Rain Accident (PG at Helsinki)

PG drop without rain & higher dose rate  re-suspension until rain “settle” the dust to the surface

Large-scale re-suspension during March 14 March 20 March

How about after the rain? PG dropped to zero on 14 and 20 March (see Poster) Daily variation with peak at local noon PG recovery despite enough ionizing radiation

Re-suspension after rain (LT=UT-9h) daily variation  re-suspension during day 21 March ~

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)

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

Check at large distance We can assume the same 131 I/ 137 Cs ratio  Ratio of dose rates approached to unity  Diffusive secondary transport

* Not approaching to unity * Episode of departing from unity  keep supplied from surroundings  from FNPP-1? / from trees? But, exception: Iitate

Anomaly events PG dropped to zero on 14 and 20 March (see Poster) Daily variation with peak at local noon Reset of recovery and daily variation: new deposition! PG recovery despite enough ionizing radiation

8 April (yes)  large-scale event 18 April (no) 26 April (?) correlation?

minor re-suspension (release) from the FNPP-1 ? 3 month after the accident

Yes!

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-contaminated 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.

Vertical Electric field = 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 Global current: 1kA Ionospheric potential:200kV (= potential gradient: PG)

q: production (by cosmic ray, radon, and  -ray) α ： neutralization β ： attaching to aerosol (density N) Ion density n: dn/dt = q - αn 2 - βnN aerosol  + positive ion         negative ion molecule

aerosol With atmospheric electric (E) field          negative ion positive ion E

Atmospheric electric field near ground Conductivity near the ground is very very low (~ /Ωm)

(00 UT) (00 UT) (00 UT) (00 UT)

(00 UT) (00 UT) (00 UT) (00 UT) (00 UT) (00 UT)

recovery phase The night-time background is returning, but this recovery resets around 8 April, 18 April, 10 May. => Rain-forced fallout from trees?

Chernobyl examples of PG change 26/4 29/4 1/5 10/5 PG at Helsinki after Chernobyl Accident Rain Accident: Plume released to north  Only one drop & with rain

cf. Past examples of PG reaction PG at Tuscon after Navada Test Shower Harris, 1955 (JGR) Shower Nuclear Tests = Wet (hard) /long distance Chernobyl = Wet (hard)/long distance + Dry/short distance Fukushima = Wet (soft) + Dry / both > 100 km

Map

(~06 UT): Earthquake (~01 UT): Venting (reactor #1) (~07 UT): Explosion (reactor #1) (~00 UT): Venting (reactor #3) (~02 UT): Venting (reactor #2) (~20 UT): Venting (reactor #3) (~02 UT): Explosion (reactor #3) (~15 UT): Venting (reactor #2) (~21 UT): Explosion (reactor #2) Time line (1): Nuclear Plant reactor cooler high-P building The explosions are by H 2 which is leaked from vent line Vent

Plume detected by Dosimeter Passage of radioactive plumes judged by radiation dose rate