Fundamental Study on Temperature Dependence of Deposition Rate of Silicic Acid − 13270

ABSTRACT The dynamic behavior of the silicic acid is one of the key factors to estimate the condition of the repository system after the backfill. This study experimentally examined the temperature dependence of dynamic behavior of supersaturated silicic acid in the co-presence of solid phase, considering Na ions around the repository, and evaluated the deposition rate constant, k, of silicic acid by using the first-order reaction equation considering the specific surface area. The values of k were in the range of 1.0×10 -11 to 1.0×10 -9 m/s in the temperature range of 288 K to 323 K. The deposition rate became larger with increments of temperature under the Na ion free condition. Besides, in the case of Na ions 0.6 M, colloidal silicic acid decreased dramatically at a certain time. This means that the diameter of the colloidal silicic acid became larger than the pore size of filter (0.45 μm) due to bridging of colloidal silicic acid. Furthermore, this study estimated the range of altering area and the aperture of flow-path in various value of k corresponding to temperature by using advection-dispersion model. The concentration in the flow-path became lower with increments of temperature, and when the value of k is larger than 1.0×10 -11 m/s, the deposition range of supersaturated silicic acid was estimated to be less than 20 m around the repository. In addition, the deposition of supersaturated silicic acid led the decrement of flow-path aperture, which was remarkable under the condition of relatively high temperature. Such a clogging in flow paths is expected as a retardation effect of radionuclides

Bafilomycin A1-sensitive pathway is required for the maturation of cystic fibrosis transmembrane conductance regulator

AbstractCystic fibrosis (CF) is the most common lethal genetic disease in Caucasians caused by the trafficking defects of CF transmembrane conductance regulator (CFTR), which is a cAMP-dependent Cl− channel at the plasma membrane. The trafficking pathway of CFTR is thought to be non-conventional because CFTR maturation is inhibited by the dysfunction of syntaxin 13, which is involved in protein recycling via endosomal pathway. In this study, to clarify whether the endosomal trafficking is required for CFTR maturation, we utilized a specific vacuolar H+-ATPase inhibitor, bafilomycin A1 (BafA1), which inhibits the protein trafficking from early endosome. Our data showed that low concentration of BafA1 (50nM) decreased the expression of mature CFTR but induced the accumulation of immature CFTR in the juxta-nuclear region containing an early endosome marker. Pulse-chase analysis showed that BafA1 inhibited the maturation of CFTR, but it slightly stabilized immature CFTR. These results indicate that BafA1-sensitive pathway is required for CFTR maturation and emphasize that endosomal trafficking pathway might be involved in the maturation of CFTR

A model of local distribution of saturation in a fractured layer, and its application

This paper describes a model of local distribution of liquid water (or steam) saturation in a fractured layer. The model, based on the Bernoulli trials as a probability density function of saturation, gives the following relation between the average value of the relative permeability for the water phase, k{sub rwa}, and the arithmetical mean of saturation, S{sub wa}: k{sub rwa}=S{sub wa}{sup m} where m is an index representing the non-uniformity of saturation (1<=m<=4). When m=4, the saturation is distributed uniformly. The proposed model also gives the average value for the relative permeability of the steam phase, k{sub rga}, as follows: k{sub rga}=1-S{sub wa}{sup m}-2S{sub wa}+2S{sub wa}{sup (2m+1)/3} These relations are applied to analysis of some experimental data already reported by the authors. Also, this presentation shows the validity of the Bernoulli trials as a density probability function of saturation in comparison with other kinds of such functions: the normal distribution, the triangle distribution and the beta distribution

MIMURA,“Dynamic behavior of silicic acid in the co-presence of the solid phase and Ca ions,”

ABSTRACT A main concern about cement materials for the construction of the repository is altering the groundwater to high alkalinity around the repository. Under such chemical condition, the behavior of the silicic acid is one of the key factors to estimate the initial condition of the repository system after the backfill. Since the solubility of silicic acid is extremely large in pH larger than 10, the silicic acid is supersaturated by mixing with the surrounding groundwater (pH 8). Supersaturated silicic acid would produce the polymeric silicic acid even in the presence of a solid phase (i.e., the flow-path surface). Such polymeric silicic acid also deposits gradually onto the flow-path surface while flowing downstream from the repository. However, the precipitation (or deposition) alters the surface to an amorphous one, which in turn strongly affects the sorption behavior of radionuclides. To estimate the spatial spread of the altered surface around the repository, this study examined the dynamic behaviors of supersaturated silicic acid in the co-presence of the solid phase and Ca ions. To determine the concentrations of both soluble silicic acid and its polymeric (colloidal) form in the solution, this study used the silicomolybdenum-yellow method and ICP-AES. As a silicate mineral, Mallinckrodt silicic acid powder (SiO 2 •0.23H 2 O, specific surface area 350 m 2 /g) was used. A Na 2 SiO 3 solution was diluted to a given concentration as a sample solution (pH&gt;10), then the pH value of the solution was adjusted to 8 in the co-presence of the solid phase and Ca ions (1.0 mM). The amount of solid phase was within the range of 0.1 g to 1.0 g. The concentrations of the soluble silicic acid, the polymeric silicic acid and Ca ions in the solution were monitored. This study evaluated the decrease rate, using the first-order reaction equation considering the specific surface area. In the results, the apparent rate constant, k, was 4.9x10 -11 m/s, smaller than that under the Ca ion free condition (k=2.0x10 -10 m/s). This means that Ca ions obstruct the deposition of silicic acid onto the surface. Moreover, the polymeric silicic acid was obviously observed, although the polymeric silicic acid could not be detected under the Ca ion free condition when the initial supersaturated concentration of silicic acid was less than 5 mM. In addition, the concentration of Ca ions in the solution immediately decreased down to 0.4 in WM2010 Conference, March 7-11, 2010, Phoenix, AZ 2 fraction, due to the contact with the solid phase of SiO 2 . After that, the fraction of Ca ions was kept at 0.4 in the solution. These suggest that Ca ions played two roles in producing the polymeric silicic acid in the presence of the solid phase. One is that Ca ions altered the surface of the SiO 2 solid phase by producing CSH gel on the surface of the solid phase. Such alteration affects the chemical property of the surface, also changing the surface area. The other is that the remaining Ca ions in the solution played a role in producing polymeric silicic acid as a pseudo-colloid. (Contrarily, it was confirmed that, when the Ca ion concentration exceeds 10 mM, the supersaturated silicic acid immediately produces the bridged compound and drops on the surface.) To estimate the altered surface due to polymeric silicic acid, we need a more reliable model to estimate these roles of Ca ions at less than 1.0 mM in the presence of silicic acid of a relatively low concentration such as 5 mM

Reduction in Apparent Permeability Owing to Surface Precipitation of Solutes by Drying Process and Its Effect on Geological Disposal

Disposal tunnels in geological repositories are ventilated continuously for over 50 years until their closure. Under these conditions, an unsaturated zone of mixed liquid and gas phases forms around the tunnels. Moreover, drying is assumed to progress from the host rock to the tunnels. To understand these drying processes, this study investigated the migration and precipitation of solutes via capillary forces during drying in packed columns using silica sand or glass beads as packed layers and X-ray CT analysis. In addition, the apparent permeability of a column packed with silica sand containing precipitation was examined using a flow experiment. The results indicate that the precipitation and accumulation of solutes were significant near the drying surfaces of the columns. The apparent mass transfer coefficient at a relatively early stage of the drying process indicates that the migration rate of solutes depends strongly on the capillary forces during the drying process. Furthermore, the apparent permeability of the columns with precipitation decreased significantly. These indicate that the precipitation and accumulation of solutes with drying in the groundwater reduce the porosity and permeability, and the advection of groundwater around the repository may be suppressed