Barrier function of crystalline rock

Transcription

1 12 th NAWG 2011 Barrier function of crystalline rock - Evaluation based on in-situ characterization and experiments at the Mizunami Underground Laboratory (MIU), Japan - H Yoshida* T.Tsuruta S.Nishimoto* Y.Asahara* *) Nagoya University, Graduate School of Environmental Studies, Nagoya, Japan )JAEA (Japan Atomic Energy Agency) Tono-Geoscience Centre, Mizunami, Japan 1/19

2 Analogous studies relevant to barrier function and geological stability Redox Redox front in buried gravels Fe-oxyhydroxides accumulation and elemental migration Crystalline rocks Analogue of NF geochemistry (LPG site) Fault stability Fracture NF processes Fracture development and its stability (Sealing) Redox front in crystalline rock and sedimentary rock Mass transport Host rock alteration and its retardation capacity Uranium series nuclide migration in sedimentary rock Sedimentary rocks accretionary complexes Fault and fracture barrier function Altered host rock Host rock stability Japan Specific 2/19

3 Content *Background *Characteristics of crystalline rock (URL and LPG site) -alteration, fractures and fault *Studies of the barrier function -sorption capacity of altered rock -formation processes and long-term stability -structural model relevant to nuclide migration *Concluding remarks 3/19

4 Background; Understanding of characteristics of deep crystalline rock Crystalline rocks Fault Repository Alteration zone Fractures More than 300 meters depth Repository inevitably crosses the alteration zones, fractured zone and faults in crystalline rocks in Japan. Case of MIU site; more than 50% is altered. Toki granite; up to -300m Fractures and faults MIU site The influences of alteration, secondary minerals and microfractures on chemical sorption and/or physical retardation mast be assessed to determine the barrier function. Conceptual view of panel allocation This will be necessary to assess the retardation capacity at a site and to allocate panels. 4/19

5 Fault and fracture system in crystalline rock (ex1:lpg site) Coast: Oil storage sites LPG Storage site Seto inner see depth ca 20m Fault frequency: every a few hundreds meters Depth: 200m 100m Difficulties : exclude all faults from the surface investigation 5/19

6 Alteration of deep granitic rock in Japan (case of LPG site) Alteration zone; up to 60% Depth;200m below seabed in crystalline rock Length;400m 400m Width:20m, Highth:30m Used for retardation capacity investigation Bi=Biotite Pl=Plagioclas e Qz=Quartz Kf=K-feldspar 5cm Fresh rock Altered rock Bi Bi Chl Kf Qz Pl Kf Bi Pl Fe Pl LPG cavern Kf Scale bar = 1 mm Kf Qz Bi 6/19 Fe

7 Altered rock characterization (mineralogy and pore geometry) Fresh Gr. A K-Feld B Altered Gr. Chl Fe-ox Bt Qz Qz K-Feld K-Feld a K-Feld Micro-fracture Ser K 15 0 Ca Altered Gr Fe K 15 0 Ca 20 0 Fe Microfracture development Dissolution of K, Ca and Fe-ox precipitation Bt Fresh Gr. Density Porosity /g cm -3 (%) Specific surface area/m 2 g -1 Adsorption capacity (STP)/cm 3 g -1 Average of pore diameter/nm Fresh G Pore size distributions of fresh and altered granite Altered Gr Results of pore analysis (Rock density, porosity, specific surface area and average of pore diameter) 7/19

8 Cs sorption experiments (Unaltered vs Altered rock) Fresh Gr. Altered Gr. 1 Composition of simulated groundwater [mol L -1 ] Cs NaHCO 3 CaSO 4 +5H 2 O KCl MgSO x x x x x 10-5 Solution ph 8.5 Grain size <100um Liquid/Solid ratio 10 cm 3 g -1 Sample bottle 30 ml of Poly(propyrene) bottle Sorption period Temperature 109 days with shaking 298 K Kd [m 3 kg -1 ] Fresh Gr Altered Gr1 Altered Gr2 Kd values obtained from batch sorption experiments for the series of granite samples. Experimental condition of synthetic water and solid materials used for the batch sorption experiments. 8/19

9 Flow-through experiments (Altered rock) bucket sample cup sample sample holder /capsule microdispersal cell inlet for test solution centrifuge rotor collection chamber for effluent Schematic of centrifuge system for flow-through experiment Core sample φ1.5cmx2.0cm 3000rmp Cs+ C/C 0 Kd' [dm 3 g -1 ] Where the sorption takes places. b) Altered Gr Pore volume [PV] Kd' calculated from the breakthrough curve for altered Gr K-Feld Almost same as the value from sorption exp. K-Feld Bt C/C Pore volume [PV] Breakthrough curve as a function of pore volume for altered Gr Qz 15.6 mm EPMA picture of a polished thin-section, showing accessible micro-fractures and pores (arrows) in the altered Gr, revealed in green by a contrast medium (3Na 2 WO 4 9WO 3 ; sodium metatungstate solution). The contrast medium was introduced by the centrifuge technique. K-Feld;Potasium-Feldspar, Qz;Quartz, Bt;Biotite. 9/19 Qz

10 Summary and conclusion (1);altered host rock Crystalline rocks Fault Repository Alteration zone Fractures More than 300 meters depth Repository inevitably crosses the alteration zones along the fractured zones and faults in crystalline rocks in Japan. Altered host rock; Alteration occurs widely along fractures and fault zones in deep crystalline rocks distributed in the orogenic area of Japan and will be encountered when a repository is constructed within crystalline host rock. Retardation capacity of altered Gr; The investigation results give insights into radionuclides retardation processes to be occurred in any altered and fractured crystalline rocks. It is not necessary to exclude areas with alteration when allocating disposal panels in a repository constructed in an orogenic field/japan. Conceptual view of panel allocation 10/19

11 Fault and fracture system in crystalline rock (ex2: URL site) MIZ-1 DH-2 F-1(in shaft) Depth Mizunami-G. Crystalline rocks Toki-Gr. Alteration zone Fractured zone Intact zone Fault Repository Fractures More than 300m deep Repository inevitably crosses the fractured zone and faults in crystalline rocks in Japan. Faults Fault Use the knowledge to develop a realistic conceptual model Conceptual view of panel allocation (NUMO) 11/19

12 Characterization of fault and fracture system (MIU site) Photo① Photo② Photo③ Alteration analysis Fracture and filling analysis Fracture and filling analysis Photo④ Photo① Photo② Photo③ Hydraulic test Fault and gauge analysis Fault plane Alteration analysis + Sorption exp. Photo④ 12/19

13 Fractures: Process of formation (fracture fillings) Relationship between wall rock alteration and fracture filling formation Dissolution mail Occurrence of crystal type Precipitation main Nishimoto & Yoshida (2010) Lithos Ca,K,Fe from rock matrix used as sources of filling mineral formation. 13/19

14 Process of fracture and fault formation in crystalline rock Ex. Kakkonda Gr. (Sasaki et al.2003) Fault and fracture frequencies are higher than continental type granite. Fracture fillings: Qz, Epi. Chl. Feldspar:Ca reaching Illitization Bt K reaching Chloritization Fracture fillings: Chl. Zeo. Cal. Feldspar:Ca reaching, Smectization Bt Fe reaching Fracture fillings:fe & Mn oxides Bt Vermiculite Yoshida (2011 in press. This concept is adaptable in plutonic crystalline rocks in Japan. Fracture and fault Stability analysis 14/19

15 Long-term stability analysis of fault (dating of fault gauge) Gauge with host rock breccia Gauge without brecciate materials M403.7R-SE M232.4E M292.8R M252.9R < Clay minerals Scale bar = 5mm Rb-Sr dating method applied both clay minerals 15/19

16 Activity estimated by dating of fault gauge Part of without breccia ca.50ma Close temperature ( ) Each age estimated by different method relevant to each thermal evidence in Toki-Gr. Altered rock Apatite Fission track age Gauge Sr-R age Age (Ma) Dyke Zircon age Monazite U-Pb age ±2.0Ma ±2.0Ma Alteration, fracturing and faulting of Toki granite during the formation Ground surface MizunamiG. Ground surface Part of with breccia ca. 33Ma Ground surface ca.30ma~; Low-T thermal alteration ca.50ma;faulting and thermal alteration ±0.2Ma ±1.4Ma ca.70ma; intrusion Host rock alteration Rb-Sr age (fault gauge time 16/19

17 Hydrological properties in and around fault in crystalline rock High conductive zone Conductivity around the fault Fault gauge: low conductivity Fractures in the altered zone around the fault: low conductivity (due to the clayey filling minerals) Fractures in the fresh host rock; relatively higher conductivity (the zone developed asymmetry along the fault) 4.6E-07(m/sec) 2.9E-07 Low conductive zone 2.4E E E-11 17/19

18 Conceptual structural model relevant to nuclides migration Fracture and alteration zone symmetry structure Fault Brecciated gauge zone Host rock Clayey fillings Altered zone Applied to in-situ experiment in MIU site Fault zone asymmetry structure Fracture fillings Several meters Fresh zone Altered zone W;width ρ porosity Kd; sorption capacity 18/19

19 Concluding remarks Fault and fractures in crystalline rock *Understanding of formation processes Specific distribution geometry of fault and fracture Concept can be transfer to the site characterization Barrier function of crystalline rock *Certain sorption capacity expected in altered host rock *Long-term stability of faults and fractures by characterization of fillings (texture, dating and geochemistry) *Development of the structural model relevant to nuclide migration Knowledge of MIU site data is important to prepare for orogenic underground realistic structure and environment. 19/19