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M. Yamauchi , M. Takeda, M. Makino, T. Owada

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

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M. Yamauchi , M. Takeda, M. Makino, T. Owada

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  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)

  5. Overview (PG+dose 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 @ 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

  9. Re-suspension after rain (LT=UT-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 (?)

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

  17. Yes!

  18. 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.

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

  20. Ion density n: dn/dt = q - αn2 - βnN q: production (by cosmic ray, radon, and -ray) α：neutralization β：attaching to aerosol (density N) negative ion positive ion  + +   + + +  aerosol   + +   +  + molecule

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

  22. Atmospheric electric field near ground Conductivity near the ground is very very low (~ 10-14/Ωm)

  23. 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)

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

  26. 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

  27. 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 > 100 km

  28. Map

  29. 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

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

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