福島の避難区域の環境放射能…何が起きているか？
What is happening to radioactivity in theenvironment of the Fukushima exclusion
zone?

アレクセイ・コノプリョフ
福島大学 環境放射能研究所教授

Aleksei Konoplev

Institute of EnvironmentalRadioactivity
Fukushima University

Worldwide 131I and 137Cs deposition

After Marzo, 2014

堆積における初期r-Cs化学形態
Initial r-Cs chemical forms in the fallout
Chernobyl: insoluble fuel andsoluble condensation particles

After Salbu, 1996

Fukushima: soluble
condensation particles, but also
insoluble glassy hot particles –“Cs balls”: 48-318 particles per gsoil; 8.5-32% of radioactivity(Ikehara et al., 2018)

After Abe, Adachi et al., 2014

土壌・堆積物中のr-Cs保持の概念モデルとその化学形態の変換
Conceptual model of r-Cs retention in soils and sediments andtransformation of its chemical forms

𝑪𝒕𝒐𝒕𝒔 (𝒕)𝒕𝒐𝒕
𝑲𝒅 (𝒕) =𝑪𝒘 (𝒕)

𝑪𝒆𝒙
𝒔 (𝒕)
𝒆𝒙
𝑲𝒅 (𝒕) =𝑪𝒘 (𝒕)4誤って放出された放射性核種の環境中での運命と輸送
Fate and transport of accidentally released radionuclides in theenvironment

Study areas and observation sites inFukushima Exclusion Zone

Rivers: Abukuma, Niida, Maeda
Dam Reservoirs: Sakashita, Yokokawa
Ponds: Inkyozaka, Suzuuchi, Funasawa, Kashiramori (Okuma);
Shimofukazawa, Biwa (Futaba)福島の流域からの放射性セシウムの流出

Radiocesium wash-off from the catchments of Fukushima
Data of JMA

Mean annual precipitation at 5 meteo-stations inFukushima Exclusion Zone, mmHaramachi
Namie
IitateTsushima
Tomioka1380±190

1490±2001310±190

1450±160

1590±70

Generally, relatively high precipitation, air temperatures and steep
slopes in the region promote higher wash-off of radiocesium andrelatively fast natural attenuation.

Niida River: R-Cs vertical distribution on
floodplain – accumulation and lossGrass matts installation
for sediments collectionExtreme floods during tropical storms as a factor ofsediments redistribution and natural decontamination

Natural attenuation due to extreme
flood events in Fukushima

N6: During several days of extreme flood in September 2015
accumulation of sediments occurred for 35-40 cm

Dose rate at h=1 m:
After 2015.9.16
Before 2015.9.16
0,85 µSv/h
6 µSv/hFieldwork on Abukuma riverin 2018

Changes in riverhydrochemistryfrom upstream
to the mouthcause r-Cs
remobilization

Irrigation ponds in close proximity of FDNPP(Konoplev et al., 2016; Wakiyama et al., 2017)

Okuma town
InkyozakaSuzuuchiFunasawa

Kashiramori

FDNPP

Dynamics of annual means of dissolved
137Cs (Bq/L) in Okuma ponds

 R-Cs activity concentrations in ponds are much higher ascompared with rivers and dam reservoirs.
 R-Cs showed a persistent behavior in Okuma ponds: its activity
14
concentrations were not decreasing.

Dissolved 137Cs, Bq/L

Regular seasonal variations of dissolved 137Cs inOkuma ponds: 137Cs concentrations tend to grow inthe summer and decrease in the winter.

6Dynamics of dissolved 137Cs for Suzuuchi in2015-2017

420

2015/4/6

2015/10/23

2016/5/10

2016/11/26

2017/6/1415沈降は、水柱から底質への137Cs除去の主要な自然減衰プロセスである
Sedimentation is a key natural attenuation process of 137Cs removal fromthe water column to the bottom sediments
 There are deep reservoirs on
many Fukushima rivers at
Yokokawa Dam - Ota River,Takanokura Dam - Mizunashi
River, at Ogaki Dam – Ukedo River,
Sakashita Dam – Kuma River.
 These reservoirs in Fukushima
area play a role of the "traps" forthe contaminated sediments.

福島地域の横川ダムにおける粒子状r-Csトラップのモデリング
Modelling of particulate r-Cs trapping in Yokokawa dam of theFukushima area (Zheleznyak & Kivva)

洪水中の：横川ダムの懸濁態Cs-137濃度（左）と底質堆積物の137Cs堆積量（右）Particulate 137Cs concentration in watercolumn (left) and 137Cs deposition in bottom(right) of the Yokokawa reservoir during thehigh flood.

是正戦略の策定と意思決定のためには、⾧期的な大規模モニタリングプログラムを実施する必要があります。For
remediation strategy development and decision making thelong-term wide scale monitoring program should be in place;
福島由来のr-Csは土壌や堆積物の粒子に強く結びついています。 これは、表流水中のr-Csのより速い掃去と、表面流出と河川流を伴うまとめ
Mainmessages

懸濁物質上のr-Csの優勢な輸送を促進する。Fukushima-derived r-Cs is strongly bound by soil and sediment particles. This
promotes faster scavenging of r-Cs in surface waters andprevailing transport of r-Cs on suspended material with surface
runoff and river flow;
福島の立ち入り禁止区域における比較的高い降水量、気温、急な斜面は放射性セシウムの著しい洗い流しと汚染された流域の自然な減衰を促進する。Relatively high precipitation,
air temperature and steep slopes in Fukushima Exclusion Zone
promote significant wash-off of radiocesium and naturalattenuation of contaminated catchments;
台風時の極端な洪水は、福島県立排除区での放射能汚染の迅速かつ効率的な自己浄化をもたらします。Extreme flood
events during typhoons result in fast and efficient selfpurification of radioactive contamination in Fukushima
Exclusion Zone.

ご清聴ありがとうございました!
Thank you very much for your attention!
http://www.ier.fukushima-u.ac.jp/