Comparative modeling of an in situ diffusion experiment in granite at the Grimsel Test Site.

An in situ diffusion experiment was performed at the Grimsel Test Site (Switzerland). Several tracers ((3)H as HTO, (22)Na(+), (134)Cs(+), (131)I(-) with stable I(-) as carrier) were continuously circulated through a packed-off borehole and the decrease in tracer concentrations in the liquid phase was monitored for a period of about 2years. Subsequently, the borehole section was overcored and the tracer profiles in the rock analyzed ((3)H, (22)Na(+), (134)Cs(+)). (3)H and (22)Na(+) showed a similar decrease in activity in the circulation system (slightly larger drop for (3)H). The drop in activity for (134)Cs(+) was much more pronounced. Transport distances in the rock were about 20cm for (3)H, 10cm for (22)Na(+), and 1cm for (134)Cs(+). The dataset (except for (131)I(-) because of complete decay at the end of the experiment) was analyzed with different diffusion-sorption models by different teams (IDAEA-CSIC, UJV-Rez, JAEA) using different codes, with the goal of obtaining effective diffusion coefficients (De) and porosity (ϕ) or rock capacity (α) values. From the activity measurements in the rock, it was observed that it was not possible to recover the full tracer activity in the rock (no activity balance when adding the activities in the rock and in the fluid circulation system). A Borehole Disturbed Zone (BDZ) had to be taken into account to fit the experimental observations. The extension of the BDZ (1-2mm) is about the same magnitude than the mean grain size of the quartz and feldspar grains. IDAEA-CSIC and UJV-Rez tried directly to match the results of the in situ experiment, without forcing any laboratory-based parameter values into the models. JAEA conducted a predictive modeling based on laboratory diffusion data and their scaling to in situ conditions. The results from the different codes have been compared, also with results from small-scale laboratory experiments. Outstanding issues to be resolved are the need for a very large capacity factor in the BDZ for (3)H and the difference between apparent diffusion coefficients (Da) from the in situ experiment and out-leaching laboratory tests.

Matrix diffusion and sorption of Cs+, Na+, I- and HTO in granodiorite: Laboratory-scale results and their extrapolation to the in situ condition.

Matrix diffusion and sorption are important processes controlling radionuclide transport in crystalline rocks. Such processes are typically studied in the laboratory using borehole core samples however there is still much uncertainty on the changes to rock transport properties during coring and decompression. It is therefore important to show how such laboratory-based results compare with in situ conditions. This paper focuses on laboratory-scale mechanistic understanding and how this can be extrapolated to in situ conditions as part of the Long Term Diffusion (LTD) project at the Grimsel Test Site, Switzerland. Diffusion and sorption of (137)Cs(+), (22)Na(+), (125)I(-) and tritiated water (HTO) in Grimsel granodiorite were studied using through-diffusion and batch sorption experiments. Effective diffusivities (De) of these tracers showed typical cation excess and anion exclusion effects and their salinity dependence, although the extent of these effects varied due to the heterogeneous pore networks in the crystalline rock samples. Rock capacity factors (α) and distribution coefficients (Kd) for Cs(+) and Na(+) were found to be sensitive to porewater salinity. Through-diffusion experiments indicated dual depth profiles for Cs(+) and Na(+) which could be explained by a near-surface Kd increment. A microscopic analysis indicated that this is caused by high porosity and sorption capacities in disturbed biotite minerals on the surface of the samples. The Kd values derived from the dual profiles are likely to correspond to Kd dependence on the grain sizes of crushed samples in the batch sorption experiments. The results of the in situ LTD experiments were interpreted reasonably well by using transport parameters derived from laboratory data and extrapolating them to in situ conditions. These comparative experimental and modelling studies provided a way to extrapolate from laboratory scale to in situ condition. It is well known that the difference in porosity between laboratory and in situ conditions is a key factor to scale laboratory-derived De to in situ conditions. We also show that cation excess diffusion is likely to be a key mechanism in crystalline rocks and that high Kd in the disturbed surfaces is critically important to evaluate transport in both laboratory and in situ tests.

Glycaemic control and serum intact parathyroid hormone levels in diabetic patients on haemodialysis therapy.

BACKGROUND: Osteodystrophy is one of the long-term haemodialysis complications, and in diabetic patients, it mainly occurs as an aplastic or low-turnover type due to their low serum intact parathyroid hormone (iPTH) levels. In the present study, we investigated the role of glycaemic control to the serum iPTH levels in diabetic haemodialysis patients. METHODS: A total of 162 patients who had started haemodialysis at our hospital in the last 10 years were enrolled. Among them, 80 patients suffered from diabetic nephropathy as a primary cause of end-stage renal failure, 69 chronic glomerulonephritis, 9 polycystic kidney and 4 from other causes. We examined the serum iPTH and HbA(1c) levels of all patients at the start of haemodialysis. In 80 diabetic patients, we examined those levels both at the start of haemodialysis and 1 year later and investigated how glycaemic control affected the iPTH levels. RESULTS: The serum iPTH levels at the start of haemodialysis were significantly lower in patients with diabetes than without diabetes (P=0.032). The levels were lower in patients with poor glycaemic control than with good control (P=0.045). In the analysis of diabetic patients 1 year later, the serum iPTH levels were significantly reduced in those with poor glycaemic control (P=0.002). The multiple regression test showed that the serum HbA(1c) levels were strongly related to the serum iPTH levels (P<0.001). CONCLUSIONS: The status of glycaemic control in diabetic haemodialysis patients affects the serum iPTH levels. Good glycaemic control should be required to prevent osteodystrophy.