Cs Migration Behaviour in the Environment and Its Long-Term Assessment after Decontamination Work in Fukushima

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1 1 Cs Migration Behaviour in the Environment and Its LongTerm Assessment after Decontamination Work in Fukushima Mikazu Yui, Kazuki Iijima, Yukio Tachi, and Shinichi Nakayama Fukushima Environmental Safety Center Japan Atomic Energy Agency

2 Decontamination Implementation 2 Special Decontamination Area(>20 m Sv /y) :11 Municipalities by National Government Intensive Contamination Survey Area (1 to 20m Sv /y) by Each Municipality Funded by Government :104 Municipalities, 8Prefecturs Based on the Guidelines for Decontamination Works Issued by Ministry of the Environment

3 Special Decontamination Area and Intensive Contamination Survey Area 3 Reference: Ministry of the Environment Government Offsite Decontamination Measures WWW Document,

4 Further Studies Needed for Decontamination works 4 Decontamination for Forest Decrease in Waste Generation Waste Storage and Disposal Possible Recontamination by Weather and Water Flow Based on Understanding of Cs Behavior in the Environment: Likely Dominated by Sorption Especially on Clay Minerals in the Soil Zone

5 Cs Transport Behavior 5 Cs Sorption Significantly Affected by Ionic Strength of Aqueous Solutions Kinds of Solid phases Organic Matter More Important is Reversibility of Cs Sorption on Natural Materials Cs is Rarely Detected from Water, It Means That Cs Sorption Likely Irreversible Cs Transport Accompanied by Solid Particles, Especially in Fresh Waters

6 Cs sorption on Montmorillonite 6 K d of Cs is consistent between batch and compacted systems

Claybased Modeling Approaches Sorption model Diffusion model Bentonite Montmorillonite Homogeneous EDL Mudstone / Horonobe Smectite Illite Pore distributionedl Granite / Grimsel BiotiteChlorite EDL?

7 Claybased Modeling Approaches Sorption model Diffusion model Bentonite Montmorillonite Homogeneous EDL Mudstone / Horonobe Smectite Illite Pore distributionedl Granite / Grimsel BiotiteChlorite EDL? Heterogeneous? Soil Clay minerals Unsaturated? EDL? 7 TSM for complex substrates smectite hematite quartz quartz Variation of clay feldspar feldspar hematite smectite f hematite feldspar quartz generic surface sites for SC, IE (OECD/NEA, 2005) Component Additivity (CA model) EDL diffusion model averaged pore width basal plane homogeneous pore ionic distribution (cation excess / anion exclusion) viscoelectric effect

Clay based model approach Cs/I in Horonobe mudstone 8 8 Sorption and diffusion of Cs/HTO/I as a function of salinity Mapping of sorbed Cs (EPMA) 10 1 Claybased CA sorption model a 10 0 illite Modeled

8 Clay based model approach Cs/I in Horonobe mudstone 8 8 Sorption and diffusion of Cs/HTO/I as a function of salinity Mapping of sorbed Cs (EPMA) 10 1 Claybased CA sorption model a 10 0 illite Modeled K d GWA Kd (m 3 kg 1 ) 10 1 smectite illite GWB rock fragment Elemental map for Cs Illite particle 10 2 Measured Kd batch TD smectite GWA (0.024M) GWB (0.24M) [Cs] eq (mol m 3 )

Experimental and Modeling Approach for Cs Contaminated Soils Soil Samples 9 Distribution and Relation between minerals and Cs Sorption mechanisms of Cs on Biotite (McKinley et al.

9 Experimental and Modeling Approach for Cs Contaminated Soils Soil Samples 9 Distribution and Relation between minerals and Cs Sorption mechanisms of Cs on Biotite (McKinley et al., 2004) Sorption and desorption mechanisms Claybased model and prediction Cs sorption modeling for Hanford sediments (Liu et al., 2003) Mechanistic Understanding K d setting / uncertainty Longterm transport Decontamination Safety of storage / disposal

10 Understanding of Effect of Organic Matter on Cs Sorption 10 Dependency of Organic Matter on Cs Sorption

11 Reversibility of Cs Sorption on Natural Materials 11 Distribution of Cs137 to different sorption sites in soils (Tsukada et al., 2009) Residual (unexchangeable) Organic Ion Exchange

12 12 The Most Difficult Decontamination Work is for Forest Forest Covers about 70% of Fukushima Prefecture The Limited Forest Decontamination is Likely Realistic under Consideration of Ecosystem Conservation and Disaster Prevention like Land Slides After Decontamination Works, Longterm Investigation of Cs Behavior from the Cs Source Term, the Nondecontaminatied Forest : RiverRiver Bed Dam Reservoir Estuary System Countermeasures to Prevent Cs Transport can be also Possible.

13 Overview of the FukushimaTRACE Project 13

14 Key phenomena in the Cs transport 14

15 Investigation & Simulation Area 15

16 Dam deposits investigation: Sampling of bottom deposits and dam water 16

Thin finegrained sediment at shallow part of the dam ca.

17 Dam deposits investigation: Depth distribution of radiocaesium in the bottom deposits 17 Thick finegrained sediment at deeper part of the dam 22 cm in thickness, constant Cs conc. Thin finegrained sediment at shallow part of the dam ca. 7 cm in thickness Radioactive Cs was NOT significantly detected in any lake water samples. Vertical axis:depth(m) Horizontal axis:concentration of radiocaesium(bq/kgdry)

18 River investigation: Dose rate across the river 18

Kuma Riv. Tomioka Riv. Assessment of recontamination Longterm dose rate monitoring Cs concentration drastically decreased at the closest point to estuary in Odaka River.

19 River investigation: Cs concentration along the river 5 km Concentration of Cs in flood channel 19 Sakashita Matsukiyama Odaka Riv. Dose rate, 1m (µsv/h) on 31 st May, 2012 Ottozawa Ohkuma Town office Yonomori Park Kainosaka Ogi Dam Transport by flowing water Forests Rivers & Estuaries Dams & reservoirs Ukedo Riv. Maeda Riv. Kuma Riv. Tomioka Riv. Assessment of recontamination Longterm dose rate monitoring Cs concentration drastically decreased at the closest point to estuary in Odaka River. Coastal sandbar was NOT formed at estuary in Odaka River, but formed in other rivers. Salinity at the closest point to estuary was similar to seawater in Odaka River, but two orders of magnitude lower in Ukedo River(see next slide). Cs was possibily desorbed from soil particles near estuary in Odaka River.

River investigation: Salinity of river water Odaka River estuary Ukedo River 20 ODAR1 UKER2 UKER1 estuary Sandbar ODAR2 at low tide unit: % left bank right bank surface 0.3 0.3 0.5m 2.0 2.1 1m(0.

7 at high tide unit: % left bank center right bank surface 2.3 2.1 2.0 0.5m 2.4 2.5 2.3 1m 2.3 2.5 at low tide unit: % left bank center right bank surface 0.01 0.

20 River investigation: Salinity of river water Odaka River estuary Ukedo River 20 ODAR1 UKER2 UKER1 estuary Sandbar ODAR2 at low tide unit: % left bank right bank surface m m(0.7m) at high tide unit: % left bank right bank surface m m at low tide unit: % left bank center right bank surface m m(0.7m) at high tide unit: % left bank center right bank surface m m at low tide unit: % left bank center right bank surface m m at high tide unit: % left bank center right bank surface m m atlow tide unit: % left bank center right bank surface m m m m 0.33 at high tide unit: % left bank center right bank surface m m m(1.2m) m 0.44

21 Conclusion 21 Understanding of Cs Behavior and Practical Ways for Decrease in Waste Generation Longterm Safety Assessment due to Cs Behavior from Undecontaminated Forest are Important. Continuous / Practical R&Ds are Needed to Decrease Uncertainties in Fukushima.

Long-term Assessment of Transport of Radioactive Contaminant in the Environment of Fukushima ( F-TRACE )

Long-term Assessment of Transport of Radioactive Contaminant in the Environment of Fukushima ( F-TRACE ) K. IIJIMA, T. Niizato, A. Kitamura, H. Sato, M. Yui Fukushima Environmental Research Group Fukushima