Movements of radioactive materials that was released by the Fukushima Nuclear Accident

1. 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)

2. Three types of fallouts

3. 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?”

4. 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.

5. Measurement methods

6. 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

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

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

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

10. Effect of the propagation

11. cf. After Nuclear Test Shower PG (=vertical E-field) 12 16 20 24 4 8 conductivity (by + ions) conductivity (by - ions) Harris, 1955 (JGR)

12. cf. Conductivity after Chernobyl Tuomi, 1988 (Geophysica)

13. Nuclear Tests = Wet (hard) Chernobyl = Wet (hard)/long distance + Dry/short distance Fukushima =Wet (soft) + Dry / both > 100 km

14. Ionosphere Vi Ionosphere Vi radioactive dust cloud σ σ =2eNion μion =2eNion μion Nion Nion E E E E E’ E’ radioactive contamination Earth Earth

15. effect of global fallout of radioactive dust (nuclear test) Pierce, 1972 (JGR)

16. extra dry contamination downstream of Windscale = downstream Pierce, 1972 (JGR) Pierce, 1959 (Pure and Applied Geophysics)

17. different contaminations

18. 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

19. Time line (2): Release of Radionuclide Massive release even after large evens at the nuclear site until 21 March when first heavy rain fall at the nuclear site.

20. Time line (3): Vertical E-field (PG) Six periods of different contamination conditions 1. dry contamination, 2. blow away 3. floating, 4. wet contamination 5. minor re-suspension 6. recovery

21. PG measurement at Kakioka

22. Map

23. 2011-3-13 (00 UT) 2011-3-14 (00 UT) 2011-3-15 (00 UT) 2011-3-16 (00 UT)

24. Behavior: 3 days

25. dry contaminations

27. dry contamination phase

28. 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)

29. wet contamination phase

30. wet contaminations

31. daily variation (LT=UT-9h) cf. 2000-2009 statistics (quiet days) Israël, 1973

32. sub-surface migration

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

34. due to new fallout from trees?

35. 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

36. systematic check

38. 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

40. 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 C1=60 & C2=20 8 & 2 ratio of dose 20 & 8 8 & 3 3 & 2 days

41. approach unity, but with exceptions Takahagi = I/Cs ratio (2) Iitate = slow decay

42. Interpretation for Takahagi

43. Why is Iitate special? Wind transport (extra inflow)? If so, what is the transport distance? Extra weathering loss afterward?

44. Can wind cause daily variation?

45. 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.