A photoacoustic spectrometer, equipped with an 85 meter optical fiber, was used to perform absorption measurements of lanthanide and actinide samples, located in a glovebox. The spectrometer was tested using aqueous solutions of praseodymium and americium ions; the sensitivity for remote measurements was found to be similar to that achieved in the laboratory without the fiber.

We have developed instrumentation capable of measuring optical absorption spectra over a wavelength range of 200–1200 nm and a temperature range of 20–100°C. This fiber-optic based spectrometer generates data which allow the computation of metal-ligand equilibrium constants. Studies at five temperatures have been completed using praseodymium-diglycolate as a model system. Fundamental thermodynamic values (free energies, enthalpies, entropies) were obtained from the experimentally-determined stability constants.

Water flow in hard rocks takes place dominantly in fractures. In order to predict the transport of dissolved radioelements through a fractured rock it is necessary to take into account both the geometry of the fracture network and the hydraulic properties of the individual fractures. This paper describes a technique for studying mass transfer in a single fracture. The technique is positron emission tomography (PET) and it offers the potential for visualising quantitatively the migration of dissolved tracers. Preliminary experiments have been undertaken involving the flow of Na-22 and F-18 labelled solutions through artificial fractures. The results demonstrate that PET is well suited to this application.

The presence of laterally-extensive zones of zeolitized tuff underlying the proposed high-level nuclear waste repository at Yucca Mt., Nevada, has focused attention on the potential role of zeolite minerals, particularly clinoptilolite, in sorbing radionuclides and thereby retarding their migration. Ion exchange between zeolites and aqueous solutions depends on factors including compositions of the aqueous and zeolite phases and solution concentration. In addition, the thermodynamic stability of zeolite minerals and their susceptibility to diagenetic alteration also depend on aqueous and solid phase compositions. Therefore, spatial variations in zeolite compositions which have been observed at Yucca Mt., as well as natural or repository-induced changes in groundwater chemistry, may result in variations in the effectiveness of the zeolite minerals as retardation agents.

Ion exchange experiments were conducted to obtain isotherm data and to evaluate the use of thermodynamic models in describing and predicting the solid solution and ion exchange properties of clinoptilolite. The experimental data were interpreted using excess Gibbs energy models for the aqueous solution and zeolite phases to account for nonideality in the system. The results indicate that the thermodynamic models allow predictions of clinoptilolite ion exchange behavior at ionic strengths and relative concentrations for which data are absent, and provide a foundation for the interpretation of ion exchange equilibria in multicomponent geochemical systems.

Sorption and desorption measurements were made of strontium and cesium onto clinoptilolite and Calico Hills tuff. The object was to see whether there was a correlation between sorption of strontium and cesium onto Calico Hills Tuff and the clinoptilolite based on the content of clinoptilolite in the Calico Hills Tuff. If sorption onto Calico Hills Tuff is solely due to the presence of clinoptilolite, then the ratios of the sorption ratios on tuff to those on clinoptilolite at similar conditions should be the weight fraction of the clinoptilolite in the tuff. Since the tuff contained about 50% clinoptilolite, the ratios would be expected to be about 0.5 if sorption was due solely to clinoptilolite. The experimental evidence showed that the ratios were generally near 0.5 for both cesium and strontium sorption and that ion-exchange processes were operative for both the clinoptilolite and the tuff. However, the ratios differed to a small extent for different conditions, and there were indications that other sorption processes were also involved.

The effects on sorption on geological media caused by the presence of materials derived from a cementitious repository have been studied. This work includes an investigation of the influence of cellulosic degradation products on the sorption of tin and radium on London clay and Caithness flagstones and the sorption of radium as a function of calcium concentration.

Experimental conditions were chosen to simulate those expected close to a cementitious repository (pH=l1) and at the edge of the zone of migration of the calcium plume (pH=8). Work was carried out, (i) under baseline conditions in the absence of organic materials; (ii) with gluconate, acting as a well-characterized organic degradation product simulant; (iii) with authentic cellulosic degradation products.

This investigation has shown that the sorption of tin can be affected by the presence of cellulosic degradation products whereas the sorption of radium is little affected. The sorptive behaviour of radium is however strongly influenced by the calcium concentration.

Models of the transport of sorbing radioelements through geological materials have been developed. These models couple a surface-complexation model of sorption processes with transport simulations in the CHEQMATE code. The chemical model has been shown to reproduce trends observed in batch sorption experiments. This approach may ultimately be used to investigate possible limitations to the use of models using simple Kds in repository safety-assessments. The main aim of the study reported in this paper is to increase confidence in the use of the coupled models. Simulations of through-diffusion experiments of uranium with London clay and plutonium with sandstone are presented. In both cases gluconate is present, as a simulant of organic degradation products of cellulose likely to be present in a low- or intermediate-level waste repository.

In laboratory experiments immobilisation of Tc under oxic conditions was observed. The transport behaviour of redox-sensitive elements is not only controlled by the geochemical “frame conditions” which can be measured within the macro environment. Immobilisation behaviour of Tc strongly depends on micro environments and on microbial metabolism. Micro environments which may develope on the mineral surfaces can detoriate the mobility of Tc, furthermore the fixation of Tc is influenced by microbial activities.

The effects of trace contents of 15 elements in the sedimentary rocks on the Rs- and Rd-values (Maass, 1983) of the dissolved radionuclides of the elements C (as carbonates), Se, Sr, Tc, I, Cs, Pb, Ra, Ac, Pa, U, Np, Pu, Am. and Cm were investigated and discussed. For this purpose Sr, Ba, B, Corg., Pb, P, F, Cu, Zn, Cd, V, Mn, Fe, Co and N1 contents in the rocks were compared to the sorptlon/desorption coefficients of the above mentioned 15 radionuclides and plotted in x-y diagrammes (a total of 225). While the magnitude of most trace element contents has no or only a slight influence on the retention properties of most radionuclides, a distinct correlation between the trace element contents and the magnitude of the distribution coefficients was found for some radionuclides. Particularly copper, organic carbon, and barium are found to take a positive influence on the Rs-/Rd-values of certain radionuclides. The presence of other trace elements (eg. B and F) can have a negative effect on the retention behaviour of the rock matrix as regards certain dissolved radionuclides. Seen as a whole, the magnitude of the desorption coefficients (Rd-val-ues) appears to be more closely correlated to the trace element contents than to the sorption coefficients (Rs-values).

Characteristics of the migration of 85Sr and 137cs in a solution of pH 12 through coastal sandy soil have been investigated by both column and batch tests. Desorption behaviors of the 85Sr and 137Cs by the sandy soil in both column and batch tests were examined by sequential extraction techniques, in order to study difference in the adsorption behavior of the 85Sr and 137Cs under dynamic (column) and static (batch) conditions. The dominant components of the sandy soil to the adsorption of the 85Sr ancj 137Cs were tested in batch tests.

The adsorption of the 85Sr by the sandy soil was a function of pH, while that of the 137Cs was independent of pH of the solution. Most of the 85Sr was reversively adsorbed with the sandy soil under both static and dynamic conditions. Approximately 85 percent of the 137Cs was irreversibly sorbed by the sandy soil in the column test, which was greater than that in the batch test. The desorption behaviors of the 137Cs adsorbed by kaolinite and by sericite resembled that of the sandy soil. Most of the 85Sr was reversively adsorbed by kaolinite, chlorite, sericite, FeOOH, Ti02 and Mn02 which is similar to the desorption behavior of 85Sr by the sandy soil. The distribution coefficients of the 85Sr for kaolinite, FeOOH, Mn02 and Ti02 were larger by several times than those for the chlorite and the sericite.

Therefore, the dominant components of the sandy soil contributing to the adsorption of 137Cs would be sericite, and those of 85Sr would be kaolinite, FeOOH, Ti02 and Mn02.

Results of systematic measurements on the diffusion of radionuclides through sandy, marlaceous and clayley sediment rocks from strata overlying the Gorleben salt dome are presented. The tracer nuclides used were U-233, Ra-226, Pb-210, and Ni-63. It is shown that, among other parameters, diffusion coefficients and distribution coefficients could be derived from breakthrough curves. Moreover, it is demonstrated that the diffusion behaviour of nuclides such as Pb and Ni can be enhanced enormously in sediment rocks by complex forming agents (EDTA).

Batch experiments, mineralogical studies, and geochemical modeling were conducted to evaluate the effectiveness of sphagnum peat, calcium carbonate, and hydrated lime in removing dissolved concentrations of As, Mo, NO3, and U present in uranium-tailings pore water at Gunnison, Colorado. Amounts of As, Mo, and U removal by sphagnum peat, calcium carbonate, and hydrated lime at 5.0, 2.5, and 2.5 wt.%, respectively, were typically above 97 %. Nitrate removal ranged between 55 and 80 %. Significant contaminant removal was achieved by sphagnum peat alone at pH 3.18. Addition of 2.5 wt.% calcium carbonate to the sphagnum peat-tailings system resulted in formation of soluble uranyl carbonato complexes, which decreased the amount of U(VI) fixed onto sphagnum peat by a factor of 2. Addition of 2.5 wt.% hydrated lime to the acidic tailings increased Mo concentrations by a factor of 2 under moderately alkaline conditions (pH 12). During neutralization of tailings-pore water, precipitation of ferric oxyhydroxides may provide additional removal of As, Mo, and U(VI) from solution through adsorption and coprecipitation processes.

The feasibility of in situ phosphate- and metal- (calcium, aluminum, and iron) solution treatment for 90Sr immobilization was investigated. Batch and column experiments were performed to find optimum conditions for coprecipitation of 90Sr with Ca-, Al-, and Fe-phosphate compounds in contaminated soils. Separate columns were packed with artificially 85Sr-contaminated acid soil as well as 90Sr-contaminated soil from the Oak Ridge Reservation. After metal-phosphate treatment, the columns were then leached successively with either tapwater or 0.001 M CaCl2 solution. Most of the 85Sr coprecipitated with the metal phosphate compounds. Immobilization of 85Sr and 90Sr was affected by such factors as solution pH, metal and phosphate concentration, metal-to-phosphate ratio, and soil characteristics. Equilibration time after treatments also affected 85Sr immobilization. Many technology aspects still need to be investigated before field applications are feasible, but these experiments indicate that phosphate-based in situ immobilization should prevent groundwater contamination and will be useful as a treatment technology for 90Sr-contaminated sites.

Diffusive transport rates for aqueous species in a porous medium are a function of sorption, molecular diffusion, and sample tortuosity. With heterogeneous natural samples, an understanding of the effect of multiple transport paths and sorption mechanisms is particularly important since a small amount of radioisotope traveling via a faster-than-anticipated transport path may invalidate the predictions of transport codes which assume average behavior. Static-diffusion experiments using aqueous 238U tracer in tuff indicated that U transport was faster in regions of greater porosity and that apparent diffusion coefficients depended on the scale (mm or μm) over which concentration gradients were measured in Topopah Spring Tuff. If a significant fraction of actinides in high-level waste are released to the environment in forms that do not sorb to the matrix, they may be similarly transported along fast paths in porous regions of the tuff. To test this, aqueous diffusion rates in tuff were measured for 238U and 239Pu leached from doped glass. Measured transport rates and patterns were consistent in both systems with a dual-porosity transport model In addition, filtration or channelling of actinides associated with colloidal particles may significandy affect the radionuclide transport rate in Topopah Spring tuff.

This paper addresses the problem of evaluation of radionuclide retardation in fractured rocks. Pore space around permeable fractures was examined by means of the fracture profiling technique which comprises porosity measurements and chemical analyses along the profiles perpendicular to the fracture surfaces.

Scanning electron micrographs show that the examined interfaces contain microfractures and tube-like diffusion channels. These are most frequent within 2 - 4 cm from the surface of the examined fractures. Porosity and chemistry of these interfaces are fracture specific. It is possible that diffusion into the rock matrix is restricted into the interfaces around the permeable fractures.

The microfracturing of rock matrix around fractures was studied experimentally by determining the diffusion properties of a non-sorbing tracer. The diffusivities were measured by tracer techniques using 36C1 isotope as a tracer and 0.0044 M or 1 M NaCl solutions. The diffusivities were also determined by measuring the electrical resistivities of the samples saturated with 1 M NaCl solution. The rock samples were granite around a partially filled carbonate fracture and gneiss around a slickenside fracture.

The apparent diffusivities of all the studied samples were approximately of the same order of magnitude. None of the variables, i.e. salt concentration of the solution, rock and fracture type or distance from the fracture surface, had any significant effect on the apparent diffusivities.

The effective diffusivities and porosities, on the other hand, depended strongly on the salt concentration of tha water used to saturate the rock samples. Possible reasons for this could be the alteration of the pore structure or change of the electrical double layer during the saturation of the rock with strong NaCl solution.

The geological formation surrounding a nuclear fuel waste disposal vault is an important barrier to the migration of radionuclides to the biosphere. Field investigations of plutonic rocks in the Canadian Shield have shown that open, water-bearing fractures form the main potential migration paths for radionuclides through the geosphere. Any interaction between the radionuclides in solution and the minerals in these fractures will retard radionuclide movement towards the biosphere. The minerals lining these open fractures are products of rock alteration and have themselves been subject to varying degrees of alteration over time. Accordingly, the fracture mineralogy is quite different from the bulk mineralogy of the intact host rock.

The degree to which measured radionuclide sorption varied with mineralogy was examined by laboratory sorption studies using static batch techniques and autoradiography combined with petrography. Fission products (Sr, Cs) and actinides (U, Np, Pu) were among the radionuclides studied. It was found that most fracture-infilling minerals such as hematite, goethite, illite, kaolinite, chlorite, epidote, gypsum and muscovite show preferential sorption for certain radionuclides. Calcite sorbs actinides such as U, Np and Pu from solution, but not ion exchangeable radionuclides such as Cs and Sr. Quartz shows the least affinity for any of the radionuclides studied.

It is concluded that variations in the type, amount and composition of fracture-infilling minerals must be considered in the assessment of the suitability of any geological formation as a radioactive wastes disposal site.

Radionuclides transported by ground water flowing through fractures may be delayed by interactions with the fracture surfaces. The migration of radionuclides in fractures was studied under well defined laboratory conditions using tonal-ite drill core columns with a fracture running parallel to the core axis. The hydrodynamic characterization of the columns was performed using tritiated water, pertechnetate and chloride ions as non-sorbing tracers. Strontium and neptunium were used to study the retardation of radionuclides on the fracture surfaces.

The experimental set-up is described, and break-through curves of non-sorbing tracers, strontium and neptunium are presented. The results were interpreted using models for dispersion and diffusion into the rock matrix. From the shape of the break-through curves it was concluded that for non-sorbing tracers there was very little or no diffusion at all into the rock matrix. Retardation of strontium in a column with intact tonalite surfaces indicated a Ka factor identical with that earlier determined by batch experiments. The break-through curve of neptunium indicated a non-sorbing fraction.

A radioactive tracer experiment has been performed in a highly conductive fracture zone, using a dipole geometry. Anions (131I− and 82Br−) and complexed metal ions (51Cr-EDTA, 58Co-EDTA, 111In-EDTA, 140La-DOTA, 160Tb-EDTA, 169Yb-EDTA and 177Lu-DOTA) have been injected and their properties as non-sorbing tracers were evaluated. Besides, studies of slightlysorbing cations (24Na+, 58Co2+, 86Rb+ and 201T1+) were performed. 99mTcO4 and its chemical analogue 186ReO4 were also injected to study the behaviour of Tc at low redox-potentials. Breakthrough was obtained for Re and for all metal complexes and anions. Some differences in the recovery yields could be seen. No transport of cations, except for Na, could be measured. No breakthrough of Tc could be observed. This indicates that TcO4− was reduced and sorbed.

Core samples of the Topopah Spring Member of the Paintbrush Tuff from drill hole UE25A#1 were analyzed for Sr and Nd isotopes and selected minor and trace elements to constrain the origin of a zcolitized zone associated with the lower vitrophyre. The Sm-Nd radiogenic isotope system was unperturbed by the alteration, but the Rb-Sr system was severely disturbed in the altered zone. The thick, densely welded high-silica rhyolite is remarkably uniform in composition with only a slight decrease in initial 87Sr/86Sr ratios with depth (0.7129–0.7125). Quartz latite in the upper part of the Topopah Spring has significantly lower initial Sr isotope ratios (0.7095–0.7114). Locally in the altered zone, Sr and Ca were gained in substantial amounts, and K, Rb, and Y were removed. Ti, Zr, Nb, Ba, La, Ce, Sm, and Nd were relatively immobile during the alteration. Sr added to the altered zone had an isotopic composition of 0.7119 ± 0.0002 and was probably derived from dissolution of glass in the bulk Topopah Spring (high silica rhyolite + quartz latite) and transported downward by infiltration.