Remediation strategy and capping construction for the mill

Remediation strategy and capping construction for the mill tailings pond, Ningyo-toge Uranium Mine, Japan 2012. 11. 6 ～ 11. 8 ENVIRONET Annual Forum, IAEA HQ, Vienna Hiroshi Saito Ningyo-toge Environmental Engineering Center, Japan Atomic Energy Agency

1. History and current status 2. Basic idea of remediation 3. Ongoing remediation 1

1. History and current status 2

1. 1 Location and history Japan Sea Togo Mine Ningyo-toge Mine Tottori pref. ● Okayama pref. 1955 Discovery of U outcrop 1950’s – 1960’s Exploration 1960’s – 1980’s Mining (gallery/open-pit), Milling 1987 Mine-related activities terminated Environmental Remediation commenced Ningyo-toge Mill tailings 3

1. 2 Related facilities Japan Sea Waste Storage Katamo 17 Waste Rock Yards (incl. 2 remediation completed) Waste Incinerating Facilities Ore Test Facilities Togo Mine Tottori pref. Okayama pref. Refining and Conversion Facility Asabatake Kannokura Former Openpit Mine Uranium Enrichment Engineering Facilities Chojya Ningyo-toge Toge, Yotsugi Uranium Enrichment Demonstration Plant Akawase Exhibition Hall Nakatsugo Ningyo-toge Mine Water Treatment Facility Mine-related facilities Other facilities Mill Tailings Pond Heap-leaching Facility 4

1. 3 Current status of Mill Tailings Pond History 1965 Concrete dam built on riverbed Specifications - Approved volume : approx. 40, 000 m 3 - Current volume : approx. 87% filled - Dose rate : < 1 m. Sv/y - Radionuclides’ concentration rate : 238 U : 3. 0 Bq/g 226 Ra : 16 Bq/g Current status - Stable Upstream vs Submerged Downstream - Deposit tailing from former milling facility & mining waste from water treatment facility - Impound water as a buffer reservoir - Capping under construction (ONLY for Upstream) on pit i t c e l l o c e Seepag dam Concrete 64 m Downstream Mine water Mining waste 210 m Upstream Downstream Concrete dam Upstream 鉱さいたい積場

2. Basic idea of remediation 6

2. 1 Necessity of remediation of the Mill Tailings Pond - Structural health diagnostics shows enough seismic-resistance strength - Enough space left for expected waste However …. . - The site is leased land from locals must be remediated before return - Large social impact in the event of outflow dam failure caused by earthquake - Presence is a cause for worry for locals located upstream of water-source river Concrete dam Possi ble o utflow Necessary and The highest priority 7

2. 2 Remediation strategy - Two-step strategy (Upstream --> Downstream) - Experience/data used for Downstream - Capping to reduce radon emanation & gamma radiation minimize water infiltration use natural material only - Substitute facilities before Downstream remediation Upstream Site characterization Designing Capping Downstream Site characterization Designing Confirmation of remediation effectiveness Capping plus impermeable wall? Ultimate target Monitoring No Water treatment Returning land Substitute facilities Mine water reservoir Mining waste pit 8

2. 3 The merit of Two-step strategy Why Upstream first? - Not submerged - Considerably dried / stable - Downstream could be used as a water reservoir even during remediation Mining Mine waste water Upstream Downstream submerged 9

3. Ongoing remediation 10

3. 1 Area of remediation Ends of the steep capping slope Legend Mill Tailings Pond (Upstream) Capping Gabion work Soil improvement Uncovered area No tailing deposited (original ground-surface) 11

3. 2 Specifications of Multi-layered Capping Layer Upper-filter Drain Lower-filter Protection (against erosion) Vegetation Bentonite mixture Gradient modification Material Purpose Grass seeds (only for slope) Decomposed granite soil Prevent erosion Green surface to blend in with the scenery Sand Prevent clogging of Drain-layer Gravel Drain penetrated rainwater laterally Decomposed granite soil Prevent outflow of swollen Bentonite Mixture of decomposed granite soil and bentonite (>17. 2%） Lower dose-rate and Rn emanation Decomposed granite soil Contour the structure of capping - Studied in radioactive waste disposal fields - Swelling property Contoured (5%) Drainage channel Mill tai lings Drainage channel 12

3. 3 Construction (1) Bentonite mixture layer Wa ter Pump Hopper/Feeder (Decomposed (Bentonite) granite soil) Crusher/ Mixer Bentonite mixture layer Mixture of Bentonite and Decomposed granite soil compaction CONTROL Mixture rate (Bentonite > 17. 2%) Grain size (max. <10 mm) Thickness Hydraulic conductivity (< 1. 0× 10 -9 m/s ) Degree of compaction (> 95%) 13

Hopper/Feeder (Decomposed granite soil) 3. 3 Construction (1) Bentonite mixture layer Hopper/Feeder (Bentonite) Surface compactor (10 t) Surface compactor (1 t) Crusher/Mixer (150 m 3/d) Mixture of Bentonite and Decomposed granite soil 14

3. 3 Construction (2) Capping Bentonite mixture Layer Drain Layer Lower-filter Layer Upper-filter Layer Vegetation Layer 15

3. 3 Construction (3) Drainage channel Expecte d cappin g surfac e 50 cm Drainage channel Around the capping Drain hole for Drain Layer (every 0. 5 m) 16

3. 3 Construction (4) Gabion work / Mattress basket - Inexpensive - Flexible to topograpy - Not impede groundwater flow Constructed at the end of the capping slope (51 m length/ 5 m high/ 4 m width)) 17

3. 3 Construction (5) Soil improvement Vibrohummer 1. 2. 3. ～ 4. Casing Gravel 5. 6. Gravel pile Gravel Compaction Pile Method 1. Set a casing under Viblohummer. 2. Penetrate a casing down to the target depth. 3. Put gravel into the casing. 4. Pull out the casing to leave the gravel. 5. Penetrate the casing again to tamp down the gravel. 6. Repeat 3. ～ 5. 18

3. 3 Construction (5) Soil improvement ater w d n u Gro flow Gravel-filled Casing Viblohummer Gravel piles after soil improvement 19

3. 4 Monitoring for confirmation of effectiveness Drainage volume -- Confirmation of expected drainage ability (Reduce load to water treatment facility) Rn emanation rate / dose rate -- Radiation evaluation Surface water Penetrated rainwater Precipitation Freezing depth Settlement amount / rate -- Long-term stability Influence on drainage ability Underground temperature -- Freezing depth Influence on Drain Layer Drainage channel Mill ta ilings 1 -year monitoring results reflected in specifications of Downstream remediation 20