Granite groundwaters

In Fig. 4 the evolution of pH and Eh (mV) for a Spanish granitic groundwater in contact with FEBEX bentonite is shown, together with the spatial distribution of the bentonite blocks. 

Initially, Oz diffuses through the bentonite and granitic domains, controlling the redox state of the system. Once 02 is exhausted, granitic groundwater controls the redox state of the system. The results of these calculations performed with the PHREEQC geochemical code (Parkhust Appelo 1999) clearly indicate that there is a substantial variability in pH/pe space along the temporal and spatial evolution of the near field of a repositoiy. This has clear consequences for the subsequent interactions with the Fe canister material and finally with the spent fuel matrix. 

Fig- 2. Radioelement concentrations in solutions contacted with powdered spent fuel (UO2 bum-up 50 MW d/kg U -y-dose rate 10 Mrad/h solid surface/solution volume ratio 1000/m at 25 °C) after sequential filtration (filter pore size 450 nm - white bars filter pore size 1.8 nm -> grey bars) solutions consist of concentrated brine (5 mol/kg NaCl) and simulated granitic groundwater (I = 2.8 x 10 1 mol/L, pH 8) (Geckeis et at. 1998). 

Degueldre, C., Pfeiffer, H. R., Alexander, W., Wernli, B. Bruetsch, R. 1996a. Colloid properties in granitic groundwater systems. I. Sampling and characterization. Applied Geochemistry, 11, 677-695. 

Proposed species in granitic groundwater are given in Table VIII. Since many of the relevant stability constants are not known, especially for actinide complexes with OH", CO32" and PO ", any final conclusive predictions of speciation in groundwater are impossible. 

Proposed radionuclide species in non-oxidizing granitic groundwater... 

Standard granite groundwater (GGW), with a composition based on reported analyses of naturally occurring groundwaters associated with granitic formations (7). 

Since iron oxides and iron oxyhydroxides are commonly found as fracture-infilling materials, samples with a particle size of 100 to lS um were contacted with granite groundwater containing ... 

The coupons were contacted with granite groundwater or brine containing six radionuclides for 28 d. The coupons were removed and the solutions assayed to determine the amount of sorbed radionuclides. 

OXYHYDROXIDES FORMED DURING 101 d EXPOSURE TO GRANITE GROUNDWATER... 

B. Coupon Autoradiograph after 2Bd desorption in granite groundwater... 

The interaction of cesium ions with feldspars at 150°C and 200°C has been studied in distilled water, granite groundwater and saline solution Pollucite, CsAlSi206, was identified by infrared spectroscopy, and was formed as a cubic crystalline phase. Surface analytical techniques (XPS, SAM, SIMS and SEM/ EDX) show Cs to be sorbed onto the mineral surfaces and alteration products. The mechanism of pollucite formation and its relevance to cesium transport/ retardation in the near field of a nuclear waste-disposal vault is discussed. 

The water was doubly distilled and deionized before use. Granite groundwater (G.G.W.) and standard Canadian Shield saline solutions (SCSSS) were prepared according to the method of Vandergraaf (3). 

Solute Rain Average River water Range Granite groundwater Basalt groundwater Seawater... 

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