Sorption of Cesium, Radium, Protactinium, Uranium, Neptunium and Plutonium on Rapakivi Granite
Sorption of cesium, radium, protactinium, uranium, neptunium and plutonium on rapakivi granite
Tuula Huitti, Martti Hakanen Laboratory of Radiochemistry Department of Chemistry University of Helsinki
Antero Lindberg Geological Survey of Finland
December 1996
POSIVA OY Annankatu 42 D, FIN-00100 HELSINKI. FINLAND Phone (09) 2280 30 (nat.), (+358-9-) 2280 30 (int.) Fax (09) 2280 3719 (nat.). (+358-9-) 2280 3719 (int.) ISBN 951-652-022-7 ISSN 1239-3096
The conclusions and viewpoints presented in the report ere those of author(s) and do not necessarily coincide with those of Posiva. i - POSiVa report Raportmtunnus-Reponcode POSIVA-96-23
Annankatu 42 D, FIN-00100 HELSINKI, FINLAND Juikasuaika-Daie Puh. (09) 2280 30 - Int. Tel. +358 9 2280 30 December 1996
Tekija(t) - Author(s) Toimeksiantaja(t) - Commissioned by Tuula Huitti, Martti Hakanen, University of Helsinki Posiva Oy Antero Lindberg, Geological Survey of Finland
Nimeke - Title
SORPTION OF CESIUM, RADIUM, PROTACTINIUM, URANIUM, NEPTUNIUM AND PLUTONIUM ON RAPAKIVI GRANITE
Thvistelma - Abstract
Study was made of the sorption properties of rapakivi granite at Hasholmen in Loviisa for nuclides of spent fuel. R The rock samples were taken by core drilling from the wall of the repository for operating waste and represented three different alteration stages: fresh, weathered and altered. The rock was crushed to grain size < 2 mm. Water used in the experiments was a brackish groundwater from Hastholmen. The rock material was characterized by determination of cation exchange capacities, specific areas (N2/BET) and volumetric porosities. The amounts of amorphous and crystalline iron oxides were also determined. The sorption was studied by batch method and followed as a function of time and initial element concentration. Experiments were done under both aerobic and anaerobic conditions. The Rd values of rapakivi were compared with values of the rock/water systems at the three other investigation sites for spent fuel disposal (Kivetty in Aanekoski, Olkiluoto in Eurajoki and Romuvaara in Kuhmo). No major differences were found between the sorption on rapakivi and on the other rocks in brackish or in saline water. The effective diffusion of tritiated water increased with the porosity of the rock. The measured and calculated porosity values were almost the same for the different rock types. ISBN ISSN ISBN 951-652-022-7 ISSN 1239-3096 Sivumaara- Number of pages Kieli - Language 57 + Appendices English ti _ P0SiV3 TGDOrt Raportin tunnus - Report code POSIVA-96-23 Posiva Oy Annankatu 42 D, FIN-00100 HELSINKI, FINLAND Julkaisuaika-Date Puh. (09) 2280 30 - Int. Tel. +358 9 2280 30 Joulukuu 1996 Tekijä(t) - Author(s) Toimeksiantaja(t) - Commissioned by Tuula Huitti, Martti Hakanen, Helsingin yliopisto Posiva Oy Antero Lindberg, Geologian tutkimuskeskus Nimeke - Title CESIUMIN, RADIUMIN, PROTAKTINIUMIN, URAANIN, NEPTUNIUMIN JA PLUTO- NIUMIN SORPTIO RAPAKIVIGRANIITTIIN Tiivistelmä - Abstract Hästholmenilla Loviisassa esiintyvän rapakivigraniitin sorptio-ominaisuuksia tutkittiin käytetyn polttoaineen nuklideille. Cesiumin, radiumin, protaktiniumin, uraanin, neptuniumin ja plutoniumin Rd-arvot määritettiin ja veden diffuusiota rapakivigranikissa tutkittiin. Kivinäytteet olivat kairansydämiä VLJ-loppusijoitustilan seinästä. Näytteet olivat kolmea eri muuntumisastetta: muuttumatonta, rapautunutta ja muuttunutta rapakiveä. Kivi oli jauhettu raekokoon < 2 mm. Näissä kokeissa käytetty vesi oli Hästholmenin murtovettä. Kivimateriaalin ominaisuuksia selvitettiin määrittämällä kationinvaihtokapasiteetti, spesifinen pinta- ala (N2/BET) ja tilavuushuokoisuus. Amorfiset ja kiteiset rautaoksidit määritettiin myös. Sorptiota tutkittiin batch-menetelmällä sekä hapellisissa että hapettomissa olosuhteissa. Sorptiota seurattiin ajan ja kyseessä olevan aineen konsentraation funktiona. Rapakiven Rd-arvoja verrattiin kolmelta paikkatutkimusalueelta (Äänekosken Kivetty, Eurajoen Olkiluoto ja Kuhmon Romuvaara) saatuihin tuloksiin. Rapakiven ja muiden kivien sorptio-ominaisuuksille murtovedessä ja suolaisessa vedessä ei löydetty suuria eroja. Tritioidun veden efektiivinen diffuusio kasvoi, kun kiven huokoisuus kasvoi. Huokoisuuden mitatut ja laskennallisesti saadut arvot eivät eronneet paljoa eri kivien välillä. ISBN ISSN ISBN 951-652-022-7 ISSN 1239-3096 Sivumäärä - Number of pages Kieli - Language 57 + liitteet Englanti PREFACE This study is a part of the investigation programme of Posiva Oy and was carried out in the Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki. The contact persons at Posiva were Lauri Pollanen and Margit Snellman. The responsible researchers and writers of the report were Tuula Huitti and Martti Hakanen from the Laboratory of Radiochemistry. The rock samples were chosen and analysed for mineralogy by Antero Lindberg from the Geological Survey of Finland. CONTENTS ABSTRACT TDVISTELMA 1. INTRODUCTION 1 2. MATERIALS 2 2.1. Rock samples 2 2.1.1. Sample YT5/79.35 2 2.1.2. Sample YT5/100.55 3 2.1.3. Sample YT5/165 3 2.2. Crushed rock 5 2.3. Rock slices 5 2.4. Water 5 2.5. Radionuclides 7 3. METHODS 8 3.1. Characterization of sorption materials 8 3.1.1. Determination of cation exchange capacity (CEC) 8 3.1.2. Porosity determination 8 3.1.3. Determination of amorphous and crystalline iron in rocks 9 3.1.4. Detection of nuclides 9 3.2. Sorption 10 3.2.1. Sorption experiments with crushed rock 10 3.2.1.1. Spiking of sample solutions 10 3.2.1.2. Aerobic conditions 10 3.2.1.3. Anaerobic conditions 11 3.2.2. Calculation of Rd values 12 3.3. Diffusion 13 3.3.1. Diffusion cell 13 3.3.1. Diffusion in homogeneous matrix 14 4. RESULTS AND DISCUSSION 16 4.1. Cation exchange capacity, CEC values 16 4.2. Porosity of rock 17 4.3. Amorphous and crystalline minerals 17 4.4. Rd values for the rock 18 4.4.1. Cesium 18 4.4.2. Radium 22 4.4.3. Protactinium 26 4.4.4. Uranium 30 4.4.5. Neptunium 34 4.4.6. Plutonium 40 4.4.7. Technetium 45 4.5. Diffusion 47 5. SUMMARY OF THE RESULTS OF SORPTION AND DIFFUSION EXPERIMENTS 50 6. COMPARISON WITH RESULTS FOR OTHER INVESTIGATION SITES ROCKS 51 6.1. Cation exchange capacity 51 6.2. Redox-condition of the host rocks 51 6.3. Groundwaters 52 6.4. Sorption of cesium, strontium and radium 52 6.5. Sorption of redox sensitive elements 53 6.6. Effective diffusion of water 54 6.7. Conclusion 54 7. REFERENCES 57 APPENDIX I APPENDIX II 1. INTRODUCTION This study is a part of the research programme on nuclear waste management being carried out by Posiva Oy, the company which takes care of all Finnish spent nuclear fuel. With the aim of constructing a repository deep in the Finnish bedrock, Posiva is carrying out investigations at Kivetty, at Romuvaara, at Olkiluoto, near the TVO (Teollisuuden Voima Oy) nuclear power plant, and since January 1997 also at Hastholmen in Loviisa. The aim of this study was to determine the sorption of cesium, radium, protactinium, uranium, neptunium and plutonium on rapakivi granite in the brackish groundwater of Hastholmen. The studies were carried out under aerobic (Cs, Ra, Pa, U, Np, Pu) and anaerobic (Np, Pa, Pu and Tc) laboratory conditions. The cation exchange capacity was determined for the rock and the diffusion properties were investigated by measuring the effective diffusion of tritiated water in rocks of different degree of alteration. The sorption and diffusion properties of the rocks are briefly compared with those of host rocks at other sites under investigation by Posiva for the final disposal of spent fuel. 2. MATERIALS 2.1. Rock samples Rapakivi granite from near the Hastholmen power plant was chosen for the sorption experiments. Core sample YT5 was taken from an almost horizontal drillhole 110 metres below the ground surface, from the repository under construction for low- and intermediate- level reactor waste. Core length was 168 m and diameter 42 mm. The dominant type of rapakivi at Hastholmen is pyterlite, which contains very coarse (100 - 120 mm) phenocrysts of potassium feldspar in medium-grained (5 - 10 mm) ground mass. The phenocrysts are typically angular and without a plagioclase mantle, but there are always a few small phenocrysts with mantle. Ovoids, round phenocrysts with distinct plagioclase mantle, are typical of the other rapakivi type, wiborgite. Even-grained varieties of rapakivi commonly cut the older porphyritic and coarse-grained varieties. The drill core YT5 contains only narrow even-grained dikes. Drill core YT5 includes some fractures and densely fissured zones, where the rock is also chemically altered and partly weathered. The most distinguishing feature of the altered rock is the brownish colour of iron hydroxide (goethite) or iron oxide (hematite). Small (hair-like) fissures, which are tight and partly coated with chlorite and epidote, characterize the altered rock. In more highly weathered places, plagioclase has altered to clay (kaolinite) and the pores of the rock are visible macroscopically. Three different samples were chosen for the sorption experiments: fresh pyterlite (79.30 - 79.95 m), altered but still unbroken pyterlite (164.90 - 165.60 m) and a weathered and fractured rock (100.00 - 100.80 m). 2.1.1. Sample YT5/79.35 Sample YT5/79.35 is a porphyritic rapakivi with slightly rounded potassium feldspar phenocrysts 1 to 8 cm in diameter. The groundmass consists of plagioclase, quartz, biotite, potassium feldspar and hornblende of grain size 0.2 - 5 mm. In addition, in the study of a 3 thin section muscovite, chlorite, epidote, fluorite, apatite and opaques were observed as accessory minerals. The mineral composition is shown in Table 1. The texture of this sample is undisturbed, with subhedral minerals, which means that the fracturing of the bedrock (seen in other samples) was limited to certain zones. Quartz does not show any undulatory extinction, for example. Some "normal" alteration, such as sericitization of plagioclase and biotite formation on the borders of hornblende grains, was observed. 2.1.2. Sample YT5/100.55 Sample YT5/100.55 was taken as near a fracture zone as possible to get a 10 cm piece of rock. The fracture zone is an old breccia with many both open and cemented fissures, typically brown (hematite) and greenish (clay). Thin section study revealed crushed quartz and bent biotite (chlorite) flakes. Potassium feldspar contains hematite as irregular spots. Thin section study showed the main minerals to be potassium feldspar (one large phenocryst), plagioclase and quartz. Biotite is largely altered to chlorite, which is the most common secondary mineral, but in Table 1 also clay minerals (kaolinite, for example), which cannot be distinguished optically, are calculated as chlorite. Likewise the opaque minerals of this sample are secondary, as segregation from altering mafic minerals. Accessory minerals include fluorite, apatite, primary muscovite and possibly epidote. 2.1.3. Sample YT5/165 Sample YT5/165 is from a heavily fissured zone of the drill core, where hydrothermal alteration has changed the colour of the rock to reddish brown and the porosity is easily observed. Thin section study, indeed, showed that the feldspars are less altered than the second sample (YT5/100.55). Plagioclase is slightly sericitized but not clayish; potassium feldspar is fresh. Biotite is only slightly chloritized, but hornblende has entirely altered to chlorite also in this sample. Possibly the amount of chlorite given in Table 1 includes some 4 clay mineral (kaolinite). Quartz is clear, and fractured but not recrystallized. A very dense fissuring can be seen in the thin section and fissures are filled by hematite/goethite and clay. The mineral composition of the thin section is dominated by a potassium feldspar grain (20 mm in diameter). Other minerals are plagioclase and quartz. Biotite is an accessory, as are muscovite, epidote, opaques, carbonate, fluorite and apatite. Table 1. Mineral compositions of thin sections from drill core YT5 (vol.-%), calculated by point counting method (500 points/thin section). Hastholmen, Loviisa. Drill core length 79.35m 100.55m 165m Fresh Weathered Altered Minerals Quartz 32.2 16.2 16.6 Potassium feldspar 28.6 46.4" 68.6" Plagioclase 26.6 17.2 7.6 Biotite 3.8 4.2 1.4 Hornblende 5.2 - - Muscovite/sericite 1.2 0.8 1.2 Chlorite 1.2 12.42) 2.62) Epidote 0.4 + + Fluorite + 0.6 0.4 Apatite 0.4 + + Carbonate3' - - 0.2 Opaques 0.4 2.24) 0.4 100.0 100.0 100.0 Remarks: 1) One large potassium feldspar grain (phenocryst) in the thin section. 2) "Chlorite" includes unidentified clay mineral(s). 3) Calcite or dolomite, only small massive grains between the main minerals. 4) Part of the opaques have been formed through hornblende alteration. 2.2. Crushed rock The rock for the sorption experiments was crushed to grain size < 2 mm. The specific areas of the crushed rock were measured for two-gram samples, using a Quantasorb or a Flowsorb 2300 II gas adsorption device, both based on BET-method. Measurements were repeated three times and the specific area was the average of these values. The samples were pretreated in nitrogen flow for one hour at 110°C. Table 2. Specific area (m2/g) of crushed rock. Rock Specific area (m2/g) Specific area **) *) YT5-1, fresh 0.30 0.31 av. 0.31 0.91 YT5-2, weathered 2.14 4.88 av. 3.51 2.00 YT5-3, altered 0.91 1.08 av. 1.00 1.36 *) specific area determination made before spiking (Helsinki University of Technology, Laboratory of Mineral and Particle Technology) **) specific area determination made after three weeks equilibration with groundwater (Tampere University of Technology, Engineering Geology) 2.3. Rock slices Rock slices, 15 mm thick, were cut from the drill cores with a low speed diamond blade saw. The slices were washed in an ultrasound bath and dried in vacuum. The same slices were used in the porosity determination and the diffusion experiments. 2.4. Water The groundwater from Hastholmen was taken from groundwater station LPVA2 from the wall of the repository tunnel under construction for operating waste. The station is located between piles 800 and 900 in the upper fracture zone. The groundwater station consists of a 15.7-metres-long borehole drilled from the tunnel into the bedrock. The entrance of the hole is sheltered with a tube, a manometer and a valve. The drilled borehole is also fitted with rubber swelling plugs, which isolate the borehole section between 8 and 15.7 m and allow a representative water sample to be taken. The water flow from the tube by its own pressure is about 7.5 1/min. The water was taken in two lots (1995 and 1996) and analysed each time (Table 3). Field measurements were begun about one week before water sampling. At sampling, the values of pH, conductivity, E^, and dissolved oxygen were 7.6 - 7.7, 1300 mS/m, -50 mV and 0.005 mg/1, respectively. The water was filtered through a series of filters, 0.8 (am, 0.45 ^m and 0.22 \xm, before analysis. Because of the large amount of iron (almost 6 mg/1) the water was unstable under aerobic conditions; before use, therefore, it was equilibrated with ambient atmosphere for one week and filtered through 0.22 \xm Millipore filter. The laboratory analyses done before and after the equilibration indicated no difference in concentration of the major cations (Appendix I). The iron concentration of the normal atmospheric equilibrated water decreased to 0.08 mg/1 in 1995 and 0.82 mg/1 in 1996 (Table 3). Table 3. Main components of the groundwater from station LPVA2 used under aerobic conditions (analysed after 1 week equilibration and filtration at 0.45 |jm; analysis in detail in Appendix I). Parameter LPVA2 1995 LPVA2 1996 Na, mg/1 2080 1990 Mn, mg/1 3.1 2.4 Mg, mg/1 239 230 K, mg/1 29 26.8 Ca, mg/1 785 760 Ba, mg/1 <0.5 <0.8 Cl, mg/1 5060 4800 SO4, mg/1 510 491 U-234/U-238 2.12 2.11 dissolv. CO, mg/1* 51 58.1 Fe,ot, mg/1 0.08 0.82 Br, mg/1 17 17 pH 7.5 7.74 TDS, mg/1 8700 8300 * Analysed dissolved inorganic carbon calculated as total CO2. With the help of an inert atmosphere glove bag, the water for the anaerobic experiments was taken directly from the water line tube into the sample vials, in the field. For the desorption experiments the water was taken into a dark glass bottle and preserved in nitrogen atmosphere. The amount of iron, Fe(II), in the water used in anaerobic experiments was 5.0 mg/1. 2.5. Radionuclides. The spiking solutions for batch experiments were either prepared in groundwater and added straight to the sample (Cs, Ra) or, if they were acid solutions (all other elements), they were evaporated to dryness on teflon strips and the strips were added to the samples. In diffusion experiments, tritium was added to groundwater in the reservoirs. Table 4. Characteristics of spiking nuclides. Nuclide Half-life Cone, mol/1 Cs-134 2.1a 10"8 Ra-226 1600 a <10"7, Ba cone. Pa-233 27 d 1013 U-233 1.6 x 105 a lO8 Np-235 1.1a 1013 Pu-236 2.8 a 1013 Tc-99 2.1 x 105 a 10"8 H-3 12.3 a 10" To increase the elemental concentrations of protactinium, uranium, neptunium and plutonium, the isotopes Pa-231, U-238, Np-237, Pu-242 were used in addition to the tracer nuclides. For cesium and radium CsCl, and BaCl2 were used. 3. METHODS 3.1. Characterization of sorption materials. 3.1.1 Determination of cation exchange capacity (CEC). The cation exchange capacity was determined by replacing the exchangeable cations of the rock sample with silver-thiourea complex. One gramme of crushed rock and 25 ml of AgTU solution were placed in a 50-ml polypropylene centrifuge tube (Sorvall). Samples were shaken continuously for 18 hours and then centrifuged (6500 G, 30 min). Ag+ and the exchangeable cations, Ca2+, Mg2*, K+ and Na+, in solution were measured by atomic absorption spectrophotometry (AAS). The CEC values were derived from the equation: CEC=T ^T1 (1) where Q = concentration of the exchangeable cation i (g/ml) Vj = volume of the water (ml) Zj = charge of the ion m; = mass of the crushed rock (g) Mi = molecular weight of the cation i (g/mol) 3.1.2. Porosity determinations Porosities were determined for the rock slices used in the diffusion experiments. After drying under vacuum at 80°C for five weeks, the slices were impregnated with water for 17 days. When rocks were weighed after 10 and 17 days, the Ag values differed for the fresh rock by <3.0% and for the weathered and altered rock by <1.4%. Slices were dried with a paper and then by blowing; weighing was done one minute after the slice was removed from the water. 9 The volumetric porosity was calculated with the equation: (2) where A g = difference between dry and wet (0 and 17 days) weight (g) V = volume of the rock slice (cm3) 3.1.3. Determination of amorphous and crystalline iron in the rocks. Amorphous and crystalline iron were separated from the crushed rock by the reagents of Tamm and Mehra & Jackson /I/ and the solutions were analysed for Fe by atomic absorption spectrophotometry, AAS. 3.1.4. Detection of nuclides. Cs-134 was measured by gamma spectrometry with a Wallac Ultrogamma 1280 (NaI(Tl) detector. Ra, Pa, U, Np and Pu were measured with a liquid scintillation counter (LSC Wallac Rackbeta, LSC Wallac Quantulus). Before Ra-226 was measured the interfering daughter nuclides were removed. The sample solutions were evaporated gently to dryness and then dissolved in 0.02 M HC1 solution for immediate LSC measurement. When there was no detectable activity in water, an LLD (lower limit of detection) /2/ was derived as the Rd value, and only a lower limit for Rd is given. 10 3.2. Sorption 3.2.1. Sorption experiments with crushed rock. 3.2.1.1. Spiking of sample solutions. Near neutral or slightly alkaline non-complexing solutions of Pa, U, Np and Pu might be unstable. Use, instead, of acidic spiking solutions would necessitate neutralizing the pH of the sample solutions with NaOH, which could cause harmful local precipitations of the elements. To avoid pH adjustment, the acidic spiking solution was pipetted onto a teflon strip and evaporated to dryness, and the spiked strips were added to the sample solution. The spike was dried on a specific place marked onto the teflon strip. The marked place was measured separately from the two ends of the strips in determining the dissolution of the spike. At the end of the sorption experiment the strip was removed from solution and leached with 1 M HC1 which was then analysed for the tracer. 3.2.1.2. Aerobic conditions The sorption of the tracer nuclides on crushed rock was studied by a batch method. Experiments in aerobic conditions were made at room temperature and ambient atmosphere. For solid/water ratio of 1/10 the samples were prepared by weighing 3.5 g of crushed rock into a 50-ml polypropylene centrifuge tube and adding 35 ml of groundwater. After equilibration with the rocks the Na, Ca, K and Mg concentrations in solution were determined by AAS. A steady state was reached in 7 - 10 days. The pH of the equilibrated water was 7.01 - 7.35, which was slightly lower than the pH in the field (7.6 - 7.7). Four parallel samples were used in most experiments. The samples were mixed continuously for fifteen minutes each hour, for two or three weeks, to achieve equilibrium between the crushed rock and groundwater. During equilibration the water was refreshed three or four times. The water was analysed for pH and the main cations to determine when equilibrium was reached. Stable isotopes (Cs) or long-lived isotopes (Pa-231, Pu-242) of the measured tracers were used to adjust the initial element concentration. Different Ra concentrations were 11 simulated by using Ba as a non-isotopic carrier. Cesium and radium spiking solutions were added directly to sample solutions, while the other spikes were evaporated to dryness on teflon strips and the strips were immersed in the sample solution. Changes in sorption were determined as a function of time in one of four parallel samples. As soon as the sorption steady state was reached, all samples were removed for the sorption measurements. The teflon strips were analysed as described above (sect. 3.2.2.1.). Solid and solution were separated by centrifuging the mixture with a high speed centrifuge (Sorvall, 6500G, 30 min). For desorption studies, as much water as possible was removed, the centrifuge tube was weighed to determine the amount of water left in the sample, and 35 ml of groundwater was added to the sample. The samples were put back to be shaken and the fourth sample was used to follow the progress of the desorption. 3.2.1.3. Anaerobic conditions. For the experiments under anaerobic conditions, 2.0 g of crushed rock was weighed into a 20-ml LSC glass vial. The vials were transferred through a vacuum chamber into an inert atmosphere glove box, where oxygen concentration was <2ppm, and stored there overnight in nitrogen atmosphere. The following day the sample vials were transported to the groundwater station, LPVA2, and filled with water running from the groundwater sampling line under nitrogen atmosphere. On the third day a teflon strip with the spike was added to the sample vial in the laboratory glove box. When the sorption was presumed (on the basis of previous experiments) to be in equilibrium the water was sampled and pH and F^, were measured. The water subsample was filtered through a 0.22 ^m Millipore filter before radioactive assay. The teflon strips were analysed as described above (sect.3.2.1.1). The filters were leached with acid (1 M HC1, or in the case of Pa 4 M HC1+0.5 M HF). In the desorption study pure groundwater was added to the sample and after equilibration the activity in water was measured. 12 3.2.2. Calculation of Rd values. The sorption percentages, S(%), were calculated from the measurements with equation: ^tracer ^tracer *total where tracer = activity concentration in the spiking solution (Bq/1) Vio«ai = total volume of the spiking solution (1) = activity in the measured subsample (Bq/1) = volume of the measured subsample (1) When the teflon strip was used, the sorption percentage was calculated from the measurements with equation: ^•tracer ^uflon ^sample S(%)= VJ^L 5-2**100% (4) where A,^ = activity of spiking solution left on the teflon strip (Bq) The sorption ratio, Rd, was calculated with equation: d 100-5(%) m 13 where S(%) = sorption percentage V = volume of water in the sample (m3) m = mass of the solid in the sample (kg) The removal of the spiking solution is not complete; some spiking solution is left with the solid phase and needs to be taken into account, especially in the case of low sorption. Thus the S(%) in the desorption experiment, Sde(%), is calculated from the activities in subsamples and sorption percentages, S, with equation: A *s+ Vr*Atmc*r *a-s)-Ade>$ampk *v. , ^^ *100% (6) sjtotal where Atracer = activity in the spiking solution S = sorption percentage/100 (from equation 4) Vr = volume of spiking solution left with the solid phase = activity in the measured desorption subsample = volume of the measured desorption subsample Vde,iotai = total volume of the desorption sample v total s,toui = volume of the sorption sample The R,, value of desorption, Rdde, can be calculated by the equation for Rd (equation 5). The error of S% is described as an absolute error. 3.3. Diffusion. 3.3.1. Diffusion cell The diffusion cell, which is made of acrylic, consists of two reservoirs, one for the HTO- spiked solution and one for collecting the tracer diffusing through. Separating the solution 14 reservoirs is the rock slice (the same slice used in the porosity determination), fixed in the middle with silicone rubber. The volume of each reservoir was 15 - 19 ml. The rock was equilibrated with groundwater during two weeks. A small amount of sodium azide was added to prevent bacterial growth during the experiment. The samples were taken after one, three and seven days and then once a week. First the spiking solution and then the collecting solution was removed from the reservoir. Pure groundwater was added to the collecting reservoir and finally the spiking solution was transferred back to the spiking solution reservoir. The activity measurements were made from an aliquot of the sample. 3.3.2. Diffusion in homogeneous matrix. When diffusion takes place in the plane of a homogenous matrix /3/, the concentration C depends on the distance, x, and time, t, and the diffusion equation, has the form (7) dx2 where Da is the apparent diffusion factor. In the stationary state the equation has the form 0 (8) dx2 If the diffusion factor D, is a constant in a planar sample with length 1 and the surface x=0 has concentration Q and the surface x=l concentration C2, we obtain, by integrating, _^L=* (9) C2-Cx I 15 where C is the concentration in the planar sample at a distance x. Concentration C changes linearly from C, to C2. The quantity Q, (Bq/m2) is defined as the cumulative diffused activity A (Bq) divided by the 2 area of the plane A (m ). For the initial condition C = C2 = 0, when t = 0, Q, approaches the stationary state according to the following equation: ICX where De is the effective diffusion coefficient and a, the capacity factor, is defined as UD where e is the porosity and Q the density of the rock, and Rd is the mass distribution factor. When t approaches infinity, the last term of the equation (10) vanishes and it follows that %-DJLt-L) (12) where L is the time lag /4/ and defined as the intersection of the asymptote on the t axis. The apparent diffusion coefficient Da is related to the time lag as follows: !=-£- (13) 16 4. RESULTS AND DISCUSSION 4.1. Cation exchange capacity, CEC values The cation exchange capacities /5/ of crushed rock samples, 0 < 0.2 mm, are given in Table 5. The numbers presented include both the total CEC values derived from changes in the Ag+ concentration and the CEC values calculated as a sum of the concentrations of the exchangeable cations Ca+2, Mg+2, K+ and Na+. Table 5. Cation exchange capacities, CEC values (meq/lOOg), of the crushed rock samples measured by AgTU method. Values for three parallel samples and the average are given. + Rock Ag+ Ca2+ K Na+ Total Ca+Mg+K+Na YT5-1, fresh rock 1.3 0.50 0.089 0.33 0.33 1.2 0.74 0.50 0.089 0.31 0.33 1.2 1.0 0.51 0.089 0.31 0.37 1.3 av. 1.0 av. 1.2 YT5-2, weathered 3.9 3.0 0.91 0.36 0.76 5.0 rock 3.6 2.8 0.93 0.36 0.77 4.9 3.6 3.0 0.99 0.36 0.81 5.2 av. 3.7 av. 5.0 YT5-3, altered 1.5 2.1 0.79 0.33 0.41 3.6 rock 1.8 2.0 0.81 0.31 0.33 3.5 1.8 2.1 0.79 0.29 0.33 3.5 av. 1.7 av. 3.5 The amount of exchangeable Ca2+ was relatively high in the weathered and altered rock: six and four times that in the fresh rock. The amount of exchangeable Na was the same in fresh and altered rock, and twice as large in weathered rapakivi granite. As the sum of cations Ca+Mg+K+Na, the CEC values were in order fresh:altered:weathered 1:3:4; so the cation capacity of the weathered rock was four times that of the fresh rock. For altered rock the AgTU method gave a lower CEC. CEC values of the fresh and weathered rock corresponded with the specific area values. In 17 the altered rock the specific area value increased faster than the CEC values. The amount of exchangeable Na in the AgTU solution equilibrated with the weathered rock was much smaller than the value of exchangeable Na derived from porosity and groundwater Na concentration. It seems that the pore water has been flushed either during drilling or at some later stage in rock handling. For the other rocks, the influence of pore water is relatively much smaller due to the smaller porosity. 4.2. Porosity of rock Porosity of the rock was determined by the water impregnation method described in sect. 3.1.2. The results are given in Table 6. Table 6. Porosity values of Rapakivi granite. Rock Sample e (V%) 1 0.29 YT5-1, fresh 2 0.29 3 0.33 av. 0.30 4 3.9 YT5-2, weathered 5 3.1 6 3.5 av. 3.5 7 0.71 YT5-3, altered 8 0.75 9 0.61 av. 0.69 The variation in the porosity values for parallel samples is due to the inhomogeneity of the rock slices. As expected, porosity was highest for the weathered rock and lowest for the fresh rock. 4.3. Amorphous and crystalline minerals. The amorphous and crystalline iron oxides were determined in three parallel samples of 18 rapakivi by phase-selective extraction. Soluble salts and exchangeable ions were determined as well, and the amount was <0.04 mg/g. Table 7. Amount of Fe-oxides in the rocks. The range of results is given in parenthesis. Rock Amorphous iron oxide Crystalline iron oxide minerals, mg/g rock minerals, mg/g rock YT5-1, fresh 1.3 (1.2-1.5) 0.17 (0.14-0.19) YT5-2, weathered 0.96 (0.89-0.99) 3.0 (2.8-3.2) YT5-3, altered 1.4 (1.2-1.5) 2.1 (2.1-2.2) The amount of amorphous iron was similar in the fresh and altered rock, and slightly higher than in the weathered rock. The amounts of crystalline iron oxides in the altered and weathered rock were, respectively, about 10 and 20 times the amount in fresh rock. In the sorption experiment (3.5 g crushed rock) the total amount of iron in the water (35 ml) could thus range from 5 to 14 mg. Such an amount of iron will dominate the sorption of many substances, when pH >7. 4.4. RH values for the rocks. 4.4.1. Cesium Cesium is an alkaline metal and in solution exists only in oxidation state +1. The sorption of cesium on geological media is mainly a cation exchange process and depends on both the pH and the ionic strength of the water. The sorption of cesium increases with pH and with decreasing ionic strength. An increasing cation exchange capacity (CEC) of the solid phase generally enhances the sorption of cesium. 19 Table 8. The sorption (S%) and desorption (Sde%) and corresponding Rd values of cesium in aerobic conditions for rapakivi granite in groundwater. The contact time was 28 days in both sorption and desorption. In desorption pure groundwater was used, resulting in changes in concentrations. Cs-conc. Sorption Cs-conc. Desorption rock mol/1 3 3 S% Rd (m /kg) mol/1 sde% Ride (m /kg) YT5-1 10"8 91.8 ± 0.2 0.11 10"8 93.7 ± 0.2 0.15 fresh 93.1 ± 0.2 0.14 91.2 ± 0.2 0.10 91.1 ± 0.2 0.10 lO"7 91.4 ± 0.2 0.11 89.4 ± 0.2 0.087 90.3 ± 0.2 0.095 IO-* 83.5 ± 0.3 0.051 lO"7 88.3 ± 0.3 0.076 81.6 ± 0.4 0.045 81.1 ± 0.4 0.044 81.3 ± 0.4 0.045 5 lO"4 36.4 ± 1.2 0.0059 io- 71.8 ± 0.4 0.026 35.1 ± 1.3 0.0055 YT5-2 10"8 97.9 ± 0.1 0.48 10"8 98.7 ± 0.1 0.78 weath. 98.1 ± 0.1 0.51 98.0 ± 0.1 0.50 97.8 ± 0.1 0.45 10"6 94.5 ± 0.1 0.17 lO"7 96.9 ± 0.1 0.33 93.2 ± 0.2 0.14 93.1 ± 0.2 0.14 lO"5 81.1 ± 0.4 0.044 10^ 89.7 ± 0.2 0.090 77.3 ± 0.4 0.035 76.9 ± 0.5 0.035 io-3 27.1 ± 1.4 0.0038 lO"4 44.8 ± 0.4 0.0084 23.0 ± 1.5 0.0031 21.0 ± 1.5 0.0028 YT5-3 10"8 97.8 ± 0.1 0.44 10"8 97.8 ± 0.1 0.47 altered 98.0 ± 0.1 0.49 97.7 ± 0.1 0.45 97.7 ± 0.1 0.43 lO"6 95.5 ± 0.1 0.22 io-7 87.1 ± 0.2 0.068 94.0 ± 0.1 0.16 93.7 ± 0.1 0.15 io-5 82.3 ± 0.4 0.047 lO"5 43.8 ± 0.4 0.0079 78.9 ± 0.4 0.038 79.3 + 0.4 0.040 10° 21.9 ± 1.5 0.0028 18.2 ± 1.6 0.0023 17.1 ± 1.6 0.0021 20 The altered and weathered rapakivi granite showed the same sorption properties at different Cs concentrations. The Rd values of the fresh rapakivi granite were one-fourth to one-third those of the other rocks. Figure 1 shows the Rj values as a function of cesium concentration and Figs.2 - 4 the Rd values as a function of time. YT5-1 •- YT5-2 -B- YT5-3 0.1 (? tr O.O1 r 0.001 Fig. 1 The sorption of cesium on crushed rock with different concentrations of inactive cesium. YT-5 is fresh, YT5-2 is weathered and YT5-3 is altered rapakivi granite. 21 ie-8 o.i 1e-7 r5 -B — 1e-6 •o DC 0.01 1e-4 O.OO1 12 18 24 30 time, d Fig. 2 Changes in sorption of cesium on fresh rapakivi granite, YT5-1, from groundwater with different Cs concentrations (mol/1). O.1 0.01 0.001 Fig. 3 Changes in sorption of cesium, on weathered rapakivi granite, YT5-2, from groundwater with different Cs concentrations (mol/1). 22 n tr time, d Fig. 4 Changes in sorption of cesium on altered rapakivi granite, YT5-3, from groundwater with different Cs concentrations (mol/1). The figures indicate that alteration increases sorption of Cs, but increase in CEC due to weathering is not followed by enhanced sorption of Cs. Sorption increases up to seven days. It is difficult, however, to distinguish between increase in sorption due to diffusion of Cs into mineral grains and that due to new surfaces exposed by abrasion. 4.4.2. Radium Radium is an earth alkaline metal and in solution is in valence state +2. The sorption mechanism is presumed to be ion exchange. Chemically radium behaves much like barium, which is often used as an analogue for radium. 23 Table 9. The sorption (S%) and desorption (Sde%) and corresponding R^ values of radium in aerobic conditions for rapakivi granite in groundwater. The contact time was 21 days in both sorption and desorption. Ba Sorption Desorption 3 Rock conc.(mol/l) S% Rd (m7kg) sd,% R^ (m /kg) YT5-1 <107 99.7 ± 0.1 >2.6 99.7 1 0.1 >2.3 fresh 99.8 1 0.1 >2.6 99.7 1 0.1 >2.2 99.9 ± 0.1 >2.5 99.6 1 0.1 >2.2 99.9 ± 0.1 >2.6 99.0 1 0.2 >2.2 io-7 99.7 1 0.1 >2.5 99.4 1 0.1 >2.5 99.9 ± 0.1 >2.6 99.1 1 0.2 >2.5 99.9 ± 0.1 >2.6 99.7 1 0.1 >2.5 99.5 1 0.1 2.1 100 1 0.1 >2.4 io-5 99.6 ± 0.1 >2.6 99.9 1 0.1 >2.5 99.9 ± 0.1 >2.6 99.9 1 0.1 >2.5 99.8 ± 0.1 >2.6 99.7 1 0.1 >2.5 99.7 1 0.1 >2.6 99.9 1 0.1 >2.5 103 99.6 ± 0.1 2.5 99.7 1 0.1 >2.5 98.6 ± 0.2 0.74 99.7 1 0.1 >2.5 99.1 ± 0.2 1.2 98.3 1 0.2 >2.5 99.2 ± 0.1 1.2 99.9 1 0.1 >2.5 YT5-2 <107 99.9 ± 0.1 >2.3 99.0 1 0.1 >1.6 weath. 99.9 ± 0.1 >2.3 98.4 1 0.1 >1.7 99.9 ± 0.1 >2.3 98.2 1 0.1 >1.6 99.9 10.1 >2.3 98.1 1 0.2 >1.7 10"7 99.9 1 0.1 >2.3 99.5 1 0.1 >2.2 99.9 1 0.1 >2.3 99.8 1 0.1 >2.1 99.9 ± 0.1 >2.3 99.7 1 0.1 >2.2 99.9 ± 0.1 >2.3 99.9 1 0.1 >2.2 105 99.6 1 0.1 >2.3 99.6 1 0.1 >2.3 99.6 ± 0.1 >2.3 99.6 1 0.1 >2.3 99.9 ± 0.1 >2.3 99.9 1 0.1 >2.3 99.9 ± 0.1 >2.3 99.8 1 0.1 >2.3 10"3 98.3 ± 0.3 0.61 99.9 1 0.1 >2.3 97.3 ± 0.5 0.37 99.9 1 0.1 >2.3 98.1 ± 0.3 0.54 99.9 1 0.1 >2.3 97.6 ± 0.4 0.44 99.7 1 0.1 >2.3 YT5-3 <10"7 99.6 ± 0.1 >2.3 98.7 1 0.2 >2.2 altered 99.9 ± 0.1 >2.3 98.0 1 0.4 >2.2 99.9 ± 0.1 >2.3 97.4 1 0.4 >2.2 99.9 ± 0.1 >2.3 98.8 1 0.2 >2.2 io-7 99.4 ± 0.1 1.9 99.9 1 0.1 >2.2 99.9 1 0.1 >2.4 99.9 1 0.1 >2.2 98.8 ± 0.1 0.88 99.9 1 0.1 >2.2 99.4 ± 0.1 1.7 99.9 1 0.1 >2.2 io-5 99.810.1 >2.3 99.8 1 0.1 >2.2 99.9 1 0.1 >2.3 99.9 1 0.1 >2.2 99.3 1 0.1 1.4 99.6 1 0.1 >2.2 99.9 1 0.1 >2.3 99.9 1 0.1 >2.2 lO3 97.7 1 0.3 0.44 99.9 1 0.1 >2.2 98.4 1 0.2 0.65 99.7 1 0.1 >2.2 96.9 1 0.4 0.33 99.9 1 0.1 >2.2 98.2 1 0.3 0.56 99.9 1 0.1 >2.2 24 The removal of Ra from solution is very fast. In fresh rapakivi there was no great difference in sorption for the different Ba concentrations; in altered and weathered rapakivi granite, however, sorption was similar for the three lowest concentrations, and clearly lower, 0.5 3 3 m /kg, at the initial Ba concentration of 10" mol/1. At other Ba concentrations Rd values were 3 higher than 2.3 m /kg. Figure 5 presents the Rd values of radium as a function of Ba concentrations, and Figs.6 - 8 show the R YT5-1 - YT5-2 —e— YT5-3 10 r cr 0.1 -B -7 -6 -5 -4 -3 -2 log [Ba] mol/l Fig. 5 The sorption of radium on crushed rock with different Ba concentrations. YT5-1 is fresh, YT5-2 is weathered and YT5-3 is altered rapakivi granite. For [Ba] < 10'3 mol/1 the lower limit of Rd is indicated. 25 15 20 25 . 30 Fig. 6 Changes in the sorption of radium on fresh rapakivi granite, YT5-1, from groundwater with different Ba concentrations, mol/1. T5 •C Fig. 7 Changes in the sorption of radium on weathered rapakivi granite, YT5-2, from groundwater with different Ba concentrations, mol/1. 26 ri or 30 Fig. 8 Changes in the sorption of radium on altered rapakivi granite, YT5-3, from groundwater with different Ba concentrations, mol/1. The original groundwater was near saturation with respect to CaSO4. The solubility of BaS04 (10"'° mol/1) was much lower than that of CaSO4. At all elevated concentrations, of BaSO4 however, and coprecipitation of Ra with BaSO4 cannot be excluded the solution becomes theoretically oversatured with BaSO4 . Because Ba and Ra are effectively sorbed on minerals /6/, sorption is nevertheless expected to be the main mechanism to remove Ra from solution. This is suggested by the lowest sorption for the highest added Ba concentration and high sorption at the lowest Ba concentration. 4.4.3. Protactinium Protactinium is an actinide with two valency states, +5 and +4. Pa(V) is stable, while Pa(IV) in solution, is readily oxidized to Pa(V) by oxygen in the atmosphere. Pa (IV) behaves much like U(IV), and forms a large number of crystalline compounds. In turn, Pa(V) resembles U(V) in its chemical properties /7/. Protactinium was studied in aerobic and anaerobic conditions. 21 Table 10. The sorption (S%) and desorption (Sde%) and corresponding Rd values of protactinium in aerobic conditions for rapakivi granite in groundwater. The contact time in sorption was 31 days and in desorption 18 days. Pa Sorption Desorption 3 3 Rock conc.(mol/l) Undissolv. S% Rd (m /kg) Rdde(m /kg) YT5-1 1013 3.3* 99.4 1 0.1 99.1 1 0.1 >0.52 fresh 1.8 99.7 1 0.1 99.8 1 0.1 >0.53 2.5 98.9 + 0.2 >0.99 99.8 1 0.1 >0.52 3.5 99.3 1 0.1 >0.99 99.9 1 0.1 >0.52 lo-io 1.7* 99.2 1 0.1 >0.98 99.9 ± 0.1 >0.53 2.4 99.7 1 0.1 >0.97 99.9 ± 0.1 >0.53 5.4 99.0 1 0.2 >0.96 99.9 1 0.1 >0.51 1.4 98.9 ± 0.2 99.4 + 0.1 >0.53 YT5-2 1013 11 * 98.8 1 0.2 0.82 99.5 1 0.1 >0.47 weath. 1.7 98.5 ± 0.2 0.69 99.2 1 0.1 >0.52 1.3 98.2 1 0.3 0.58 98.4 1 0.3 >0.53 1.2 98.2 1 0.3 0.56 99.4 10.1 >0.53 10"10 1.3* 98.8 ± 0.2 0.81 99.1 1 0.1 >0.52 2.1 98.5 1 0.2 0.70 99.1 1 0.1 >0.52 3.1 98.6 ± 0.2 0.75 99.5 1 0.1 >0.45 2.3 98.3 ± 0.3 0.60 99.1 1 0.1 >0.52 YT5-3 1013 23* 98.4 1 0.3 0.65 99.4 1 0.1 >0.52 altered 1.8 97.7 ± 0.4 0.44 98.2 1 0.3 >0.52 1.2 98.2 1 0.3 0.58 99.7 1 0.1 >0.53 0.78 98.5 1 0.2 0.70 99.4 1 0.1 >0.53 1O10 2.2* 98.6 ± 0.2 0.79 98.7 1 0.2 >0.53 1.5 98.3 ± 0.3 0.62 98.0 1 0.3 >0.53 2.6 98.7 ± 0.2 0.77 99.1 1 0.1 >0.52 0.97 98.2 1 0.3 0.56 98.6 1 0.2 >0.53 * after 3 days contact time, other samples after 31 days contact time The sorption of protactinium was about the same in altered and weathered rapakivi granite: 3 Rd values were 0.59 - 0.72 m /kg (Fig. 9 - 12). In the fresh rock the sorption was slightly 3 higher, and Rd was 1.0 m /kg. The sorption is fast. There was no difference in Rd values for the different concentrations. During the sorption experiment pH values were constant. 28 Table 11. The solubility of protactinium in anaerobic conditions for rapakivi granite from groundwater. The contact time was in sorption 45 days and in desorption 15 days. Rock Sample Undissolv. % YT5-1 41 86±8 fresh 42 97±10 43 90±9 YT5-2 44 81±8 weath. 45 85±8 46 97±10 YT5-3 47 92±9 altered 48 84±8 49 93±9 Most of the protactinium remained undissolved in anaerobic conditions on the teflon strips and thus no sorption or desorption values were obtained. E^, and pH values were constant during the experiment. In a sample consisting only of a teflon strip in groundwater, no tracer was dissolved. YT5-1 - YT5-2 -e- YT5-3 T3 %.----—------• -14 -13 -12 -11 -1O log [Pa] mol/l Fig. 9 The sorption of protactinium on crushed rapakivi granite with different Pa concentrations in groundwater in aerobic conditions. 29 01 E T5 0.1 10 15 20 25 30 Fig. 10 Changes in the sorption of protactinium on fresh rapakivi granite, YT5-1, from groundwater in aerobic conditions. Pa concentrations in mol/1. n 1e-13 1e-10 or O.1 10 15 20 25 30 Fig. 11 Changes in the sorption of protactinium on weathered rapakivi granite, YT5-2, from groundwater in aerobic conditions. Pa concentrations in mol/1. 30 5? 0.1 Fig. 12 Changes in the sorption of protactinium on altered rapakivi granite, YT5-3, from groundwater in aerobic conditions. Pa concentrations in mol/1. 4.4.4. Uranium Uranium may exist in valence states +6, +5, +4 and +3. Under oxidizing conditions the 2+ hexavalent state U(VI) is dominant and uranium exists as the uranyl ion, UO2 . Under oxic granite groundwater conditions in the presence of carbonate (2*10~3 mol/1), the species 2 4 UO2(CO3)2 ' and UO2(CO3)3 dominate /8/. The main oxidation state under reducing conditions is U(IV) /9/. The presence of Fe(II) in solution, from magnetite/pyrite or Fe(n)silicate minerals, decreases the oxygen in the water and uranium might be reduced predominantly to the tetravalent state at intermediate or low carbonate concentrations. The sorption of hydroxide complexes under oxic carbonate-free conditions appears to be highest in the pH range 5 - 8.5, and shows some concentration dependence under both oxidizing and reducing conditions 1121. 8 Under reducing conditions the solubility of UO2 ((U4O9):UO225) is about 2-4*10" mol/1 /10/. The sorption of uranium, U(IV), is comparable to that of neptunium, Np(IV), and plutonium, Pu(IV) /11/. The anionic carbonate complexes of uranium are soluble and can migrate as fast as water and penetrate deep into the rock matrix when the sorption onto rock is low /13/. Uranium was studied only in aerobic conditions. 31 Table 12. The sorption (S%) and desorption (Sde%) and corresponding Rj values of uranium in aerobic conditions for rapakivi granite from groundwater. The contact time was in sorption 26 days and in desorption 28 days. U Sorption Desorption 3 3 3 3 Rock conc.(mol/l) S% R,, (m /kg)*10" Sde% R,i (m /kg)*10" YT5-1 10 s 10.5 + 4.3 1.3 45.0 ± 2.9 8.5 fresh 9.94 ± 4.4 1.2 43.4 ± 2.9 8.0 9.16 ± 4.4 1.1 40.7 ± 3.1 7.4 9.63 ± 4.4 1.1 42.8 ± 3.0 7.9 io-7 9.10 ± 4.4 1.0 46.6 ± 2.8 8.9 10.8 ± 4.3 1.3 38.4 ± 3.2 6.5 9.41 ± 4.4 1.1 42.7 ± 3.0 7.9 9.53 ± 4.4 1.1 43.3 ± 2.9 7.8 8.98 ± 4.4 1.0 46.0 ± 2.8 8.8 10* 8.57 ± 4.4 0.98 41.3 ± 3.1 7.3 8.41 ± 4.4 0.99 40.1 ± 3.1 7.2 7.22 ± 4.4 0.82 43.8 ± 2.9 8.4 105 8.51 ± 4.4 0.98 43.0 ± 3.0 8.1 7.63 ± 4.5 0.87 34.6 ± 3.4 5.6 5.64 ± 4.6 0.62 32.8 ± 3.5 5.4 6.29 ± 4.5 0.72 34.5 ± 3.4 5.6 YT5-2 108 11.4 ±4.3 1.4 50.9 ± 2.6 11 weath. 10.6 ± 4.3 1.2 50.4 ± 2.6 11 10.4 ± 4.3 1.2 48.5 ± 2.7 10 10.4 ± 4.3 1.2 50.9 ± 2.6 11 10' 8.67 ± 4.4 0.99 37.3 ± 3.3 6.5 10.5 ± 4.3 1.2 38.8 ± 3.2 6.7 7.84 ± 4.4 0.91 42.8 ± 3.0 8.0 6.72 ± 4.5 0.79 42.1 ± 3.0 7.8 10"6 8.74 ± 4.4 1.0 41.0 ± 3.1 7.4 6.90 ± 4.5 0.80 44.0 ± 2.9 8.5 9.41 ± 4.4 1.1 46.5 ± 2.8 9.1 5.72 ± 4.6 0.65 48.8 ± 2.7 10 lO5 7.86 ± 4.4 0.91 53.4 ± 2.4 12 4.92 ± 4.6 0.56 44.1 ± 2.9 8.5 7.54 ± 4.5 0.83 45.6 ± 2.8 9.1 10.9 ± 4.3 1.2 46.0 ± 2.8 9.1 YT5-3 108 13.8 ± 4.2 1.6 46.9 ± 2.8 9.3 altered 15.4 ±4.1 1.9 47.7 ± 2.7 9.6 12.7 ± 4.2 1.5 43.3 ± 2.9 8.4 14.7 ± 4.1 1.8 48.5 ± 2.7 11 io-7 11.9 ±4.2 1.4 46.9 ± 2.8 9.8 13.3 ± 4.2 1.6 45.9 ± 2.8 9.1 12.3 ± 4.2 1.4 42.6 ± 3.0 7.9 10.7 ± 4.3 1.2 37.7 ± 3.2 6.4 lO6 11.6 ±4.3 1.3 48.0 ± 2.7 10 11.9 ±4.3 1.4 52.0 ± 2.5 12 11.4 ±4.3 1.3 43.8 ± 2.9 8.5 16.6 ± 4.0 2.0 62.5 ± 2.0 19 io-5 8.83 ± 4.4 0.99 38.9 ± 3.2 6.9 7.76 ± 4.5 0.85 29.0 ± 3.7 4.5 7.25 ± 4.5 0.81 26.8 ± 3.8 4.0 7.69 ± 4.5 0.85 32.9 ± 3.5 5.4 32 Uranium was totally dissolved from the teflon strip. The sorption of uranium was slightly higher on the altered rapakivi granite than on the other 8 3 rocks. At low concentration (10' mol/1), Rd values were 0.0012 m /kg for both fresh and weathered rapakivi granite and 0.0017 m3/kg for the altered rapakivi granite. However, no clear difference between the separate concentrations could be seen. pH was constant during the experiment. The amount of biotite was three times as great in fresh and altered rapakivi granite (3.8 - 4.2%) as in weathered rapakivi (1.4%), (Table 1.). The portion of quartz in the fresh rock was about twice that in altered and weathered rock. YT5-1 - YT5-2 -B- YT5-3 10 r T3 cr -4 Fig. 13 The sorption of uranium on crushed rapakivi granite with different U concentrations in groundwater in aerobic conditions. 33 O.O1 n 7D DC O.OO1 O.OO01 10 15 20 25 30 Fig. 14 Changes in the sorption of uranium on fresh rapakivi granite, YT5-1, in groundwater, in aerobic conditions. U concentrations in mol/1. O.1 O.O1 cr O.OO1 o.ooo 1 10 15 20 25 30 Fig. 15 Changes in the sorption of uranium on weathered rapakivi granite, YT5-2, in groundwater, in aerobic conditions. U concentrations in mol/1. 34 o.r O.O1 0.001 0.0001 Fig. 16 Changes in the sorption of uranium on altered rapakivi granite, YT5-3, in groundwater, in aerobic conditions. U concentrations in mol/1. 4.4.5. Neptunium Neptunium has three stable oxidation states, IV, V and VI, in natural waters. Np(in) is stable only at low pH in reducing conditions. Under aerobic conditions Np(V) is dominating. In + natural waters Np(V) exists as NpO2 or it forms hydroxy and carbonate complexes and + exhibits strongly pH-dependent sorption behaviour. The neptunyl cation, NpO2 , is strongly sorbed on many minerals. Under anaerobic groundwater conditions, Np(V) is reduced to Np(IV) in the presence of suitable reducing agents, and the fast removal of neptunium from + solution is caused by fast surface-mediated reduction of NpO2 to Np(IV)/14/. The sorption of neptunium was studied in aerobic and anaerobic conditions. 35 Table 13. The sorption (S%) and desorption (Sde%) and corresponding Rd values of neptunium in aerobic conditions on rapakivi granite from groundwater. The contact time in sorption was 40 days for concentrations 10"7 and 10"9 mol/1 and 28 days for concentration 10~13 mol/1. The desorption contact time was 20 days. Sorption Desorption 3 3 Rock Cone, (mol/1) S% Rd (m /kg) Rdde(m /kg) YT5-1 1013 64.4 ± 1.2 0.019 78.5 ± 1.1 0.038 fresh 56.8 ± 1.3 0.014 72.5 ± 1.4 0.028 55.3 ± 1.4 0.013 75.7 ± 1.2 0.032 57.9 ± 1.3 0.014 73.4 ± 1.3 0.029 9 io- 64.1 ± 3.6 0.019 >40.8 >0.0075 62.6 ± 3.8 0.018 >40.3 >0.0072 69.1 ± 3.4 0.024 >45.8 >0.0090 63.2 ± 1.4 0.018 >45.7 >0.0091 lO"7 60.7 ± 1.0 0.016 77.0 ± 0.9 0.036 56.5 ± 1.0 0.014 76.4 ± 0.9 0.034 61.1 ± 0.9 0.017 76.8 ± 0.9 0.035 61.1 ±0.9 0.016 76.2 ± 0.9 0.034 YT5-2 1013 62.5 ± 1.2 0.017 74.7 ± 1.3 0.030 weath. 52.0 ± 1.5 0.011 71.8 ± 1.4 0.026 53.4 ± 1.4 0.012 68.7 ± 1.6 0.023 56.4 ± 1.4 0.013 73.1 ± 1.3 0.028 lO"9 60.3 ±4.1 0.016 >37.9 >0.0064 57.1 ± 4.2 0.014 >31.7 >0.0050 45.9 ± 4.7 0.0090 £13.8 >0.0018 59.7 ± 4.2 0.016 >37.8 >0.0065 io-7 55.9 ± 1.1 0.014 71.4 ± 1.1 0.027 53.2 ± 1.1 0.012 72.1 ± 1.1 0.028 56.2 ± 1.1 0.014 71.4 ± 1.1 0.027 56.0 ± 1.1 0.013 70.7 ± 1.1 0.026 YT5-3 1013 49.4 ± 1.6 0.010 69.5 ± 1.5 0.024 altered 38.5 ± 1.9 0.0065 69.0 ± 1.5 0.023 38.0 ± 1.9 0.0064 66.8 ± 1.6 0.021 35.5 ± 2.0 0.0058 68.3 ± 1.6 0.023 io-9 61.6 ± 4.1 0.017 >44.7 >0.0082 59.4 ± 4.0 0.015 >37.7 >0.0063 42.5 ± 4.8 0.0079 £14.7 >0.0017 55.6 ± 4.2 0.013 >33.9 >0.0052 io-7 50.5 ± 1.2 0.011 73.1 ± 1.1 0.027 51.7 ± 1.2 0.012 71.7 ±1.1 0.027 50.5 ± 1.2 0.011 73.0 ± 1.1 0.027 50.5 ± 1.2 0.011 71.4 ±1.1 0.025 36 Neptunium totally dissolved from the strip at constant pH. There was no difference in the sorption at different concentrations. Alteration and weathering of rapakivi granite have no effect on sorption either. At the end of the sorption experiment, pH values were in the range 7.6 - 7.9 (at start pH 7.01 - 7.35) (Appendix 0, Table 8). Figure 17 shows the sorption of neptunium (Rd) on rapakivi granite as a function of Np concentration. Figures 18-20 show the Rd value as a function of time. YT5-1 - YT5-2 -B- YT5-3 E CC O.O1 r O.OO1 -14 -13 -12 -11 -1O -9 -8 -7 -6 Fig. 17 The sorption of neptunium on crushed rapakivi granite in groundwater in aerobic conditions. 37 O.i O.O1 1 e-13 n XI 0.001 O.OOO 1 O 5 10 15 20 25 30 35 40 Fig. 18 Changes in the sorption of neptunium on fresh rapakivi granite, YT5-1, in groundwater in aerobic conditions. Np concentrations in mol/1. O.O1 1e-13 _*: n E O.OO1 0.000 1 0 5 10 15 20 25 30 35 40 Fig. 19 Changes in the sorption of neptunium on weathered rapakivi granite, YT5-2, in groundwater in aerobic conditions. Np concentrations in mol/1. 38 u. 0.01 —©— 1e-13 a n --•-- 1e-9 •a CC -B- ie-7 O.O01 r\rsr\ i < i 1 1 1 o 10 15 20 25 30 35 40 time, d Fig. 20 Changes in the sorption of neptunium on altered rapakivi granite, YT5-3, in groundwater in aerobic conditions. Np concentrations in mol/1. Table 14. The sorption (S%) and desorption (Sde%) and corresponding Rd values of neptunium on rapakivi granite under anaerobic conditions. The contact time was 31 days in sorption and 49 days in desorption. 3 3 Rock Sample Undissolv. S% Rd (m /kg) Rdde(m /kg) % YT5-1 1 19±1 100±l >1.4 100±1 >1.5 fresh 2 25±1 100±l >1.3 100±l >1.4 3 13±1 99±1 >1.6 100±l >1.6 YT5-2 4 10±l 100±l >1.6 100±l >1.7 weath. 5 17±1 99±1 >1.5 99±1 >1.5 6 8.4+0.4 99±1 >1.6 99±1 >1.7 YT5-3 7 24±1 99±1 >1.4 99±1 >1.4 altered 8 20±l 100±l >1.4 100±l >1.5 9 15±1 100±l >1.5 100±l >1.6 39 Table 15. The sorption (S%) and desorption (Sde%) and corresponding Rd values of neptunium under anaerobic conditions on rapakivi granite. The contact time was 77 days in sorption and 49 days in desorption. 3 3 Rock Sample Undissolv. S% Rd (m /kg) Sae% Rd-de(m /kg) % YT5-1 10 1512 9811 >1.1 100+1 >1.4 fresh 11 13+2 100+1 >1.1 10011 >1.5 12 8.411.4 100+1 >1.2 10011 >1.5 YT5-2 13 1012 10011 >1.2 10011 >1.5 weath. 14 9.3±2 100+1 >1.2 100+1 >1.5 15 6.511.1 10011 >1.2 10011 >1.6 YT5-3 16 1412 10011 >1.2 10011 >1.4 altered 17 1112 9911 >1.2 10011 >1.4 18 9.512 10011 >1.2 100+1 >1.5 Under anaerobic conditions the dissolution of neptunium from the strip is not complete. In reducing anaerobic conditions the sorption is nearly 100% and the R,, values exceed 1.1 m7kg. E,, was clearly higher during the shorter contact time (31 days) than the longer contact time (77 days) and the desorptions. When the rock is in contact with the water for a longer time, the rock has an obvious reducing effect. pH values were between 7.22 and 8.52 and E,, values correspondingly -28 to -178 mV (Appendix II, Tables 2 and 4). In the sample where pure unfiltered groundwater was in contact with the teflon strip, the amount of undissolved tracer was 34% (for shorter contact time) and 15% (for longer contact time); after desorption, measurement of the activity showed that 38 - 48% of the dissolved neptunium tracer was in the precipitate of Fe-hydroxides. Although the E^, values do not point to strong reducting conditions, the behaviour of technetium /14/ indicates that the conditions were reducting enough to give Np in redox state Np(IV). More is said about the sorption of technetium in section 4.4.7. 40 4.4.6. Plutonium Plutonium has four relatively stable oxidation states, +3, +4, +5 and +6. Under aerobic condi- tions at pH 5 - 6, the dominating form is Pu(V), and in natural waters at pH 6 - 9 it is Pu(VI). At high carbonate concentration, Pu(V) carbonate complexes dominate if the pH is high, >8. Under anaerobic conditions, Pu(III) carbonate and sulphate complexes dominate at low pH, and if the pH is high, Pu(IV) hydroxides dominate /15/. The most important factors to affect the solubility of plutonium in natural waters are redox conditions, the oxidation state, pH, hydrolysis and complexing ions. In natural waters the solubility reaction of plutonium is hydrolysis. The sorption increases when pH increases the stage the hydrolysis occupies. The hydrolysis products are in dynamic state, nonstable in water and easily adsorbed on the surfaces of minerals and natural colloids. The formation of complexes with carbonate ions is very important in aerobic conditions /16/. The forms of reduced plutonium Pu(III) and Pu(IV) are strongly sorbed on surfaces, while the oxidized forms Pu(V) and Pu(VI) are only weakly sorbed /17/. The sorption of plutonium generally decreases in more oxidizing conditions /15/. Under aerobic conditions Pu sorbs more strongly on calcite, CaCO3, than on hornblende. This is due either to surface complexation of Pu(IV) carbonate on calcite or to the fact that the sorbing plutonium is in oxidized form, which sorbs on calcite. Under anaerobic plutonium does not sorb to calcite or hornblende from granite groundwater, but there is strong sorption to both from bentonite water /18/, a water with high carbonate content simulating the interaction between groundwater and bentonite (Na-montmorillonite). The sorption of plutonium was studied under aerobic and anaerobic conditions. 41 Table 16. The sorption (S%) and desorption (Sde%) and corresponding Rd values of plutonium in aerobic conditions on rapakivi granite from groundwater. The contact time was 21 days in sorption and 47 days in desorption. Sorption Desorption 3 3 Rock Conc.(mol/1) Undissolv. S% Rd (m /kg) Sde% Rdde(m /kg YT5-1 1013 12* 98.5 ± 0.3 0.71 99.5 ± 0.1 0.98 fresh 0.73 98.8 ± 0.2 0.86 99.9 ± 0.1 0.98 0.37 99.0 ± 0.2 1.0 99.3 ± 0.1 0.99 10" 47 * 96.8 ± 0.5 0.32 99.8 ± 0.1 0.87 0.39 98.7 ± 0.2 0.81 99.4 ± 0.1 0.97 31 98.1 ± 0.3 0.56 99.2 ± 0.2 0.94 0.46 99.2 ± 0.1 >1.2 98.4 ± 0.3 1.0 io-9 30* 97.6 ± 0.4 0.44 99.8 ± 0.1 0.91 1.3 99.1 ± 0.2 1.3 98.5 ± 0.3 1.0 2.4 99.2 ± 0.1 1.4 99.6 ± 0.1 1.0 YT5-2 1013 4.8* 98.9 ± 0.2 0.97 99.1 ± 0.2 >1.0 weath. 0.96 99.0 ± 0.2 1.1 98.9 ± 0.2 0.93 0.40 99.6 ± 0.1 >1.2 98.8 ± 0.2 0.89 0.57 98.4 ± 0.3 0.65 99.4 ± 0.1 >1.0 10" 41 * 98.6 ± 0.2 >0.67 99.3 ± 0.1 >1.0 1.3 98.7 ± 0.2 0.83 99.3 ± 0.1 >1.0 0.50 98.8 ± 0.2 0.87 98.9 ± 0.2 >1.0 1.5 98.9 ± 0.2 1.0 98.9 ± 0.2 >1.0 lO"9 6.8* 99.1 ± 0.2 1.2 99.3 ± 0.1 >1.1 0.83 99.1 ± 0.2 1.2 99.4 ± 0.1 >1.1 1.5 99.3 ± 0.1 1.6 99.6 ± 0.1 >1.1 0.76 99.1 ± 0.6 1.1 99.5 ± 0.1 >1.1 YT5-3 1013 6.9* 96.5 ± 0.6 0.30 97.6 ± 0.4 0.44 altered 0.85 98.7 ± 0.2 0.82 99.7 ± 0.1 >0.99 15 98.4 ± 0.3 0.66 98.9 ± 0.2 0.96 0.48 99.3 ± 0.1 >1.2 98.9 ± 0.2 0.93 10" 54* 96.9 ± 0.5 0.33 99.9 ± 0.1 >0.49 8.3 98.4 ± 0.3 0.67 99.0 ± 0.2 >0.49 0.23 99.1 ± 0.2 1.1 97.8 ± 0.4 0.48 lO"9 3.7* 99.4 ±0.1 1.8 99.6 ± 0.1 >1.7 31 99.3 ± 0.1 1.4 99.8 ± 0.1 >1.7 1.4 98.9 ± 0.2 1.0 99.5 ± 0.1 >1.7 0.45 99.3 ± 0.1 1.6 99.6 ± 0.1 >1.7 * after one day contact time, other samples after 21 days contact time 42 The solubility of the plutonium spike was not uniform under aerobic conditions. Looking at the 21-contact-days sorption, the undissolved fraction ranged from 0.23 to 31 % of plutonium. The sorption was fast and there was no clear difference with concentration nor between the fresh, weathered and altered rapakivi. The highest Rd value in the range 1.3 - 1.5 m3/kg was obtained at the highest concentration. During the sorption experiment the pH was in the range 7.3 - 8.0 (Appendix II, Table 7). In Fig. 21 the sorption of plutonium is presented as a function of Pu concentrations and in Figs. 22 - 24 as a function of time. VT5-1 •- VT5-2 —B— YT5-3 10 c cr -14 -13 -12 -11 -10 -9 log [Pu] mol/l Fig. 21 Sorption of plutonium on crushed rapakivi granite in groundwater under aerobic conditions. 43 en _*: n E •o 10 15 20 25 30 Fig. 22 Changes in the sorption of plutonium on fresh rapakivi granite, YT5-1, in groundwater under aerobic conditions. Pu concentrations in mol/I. 0.1 30 Fig. 23 Changes in the sorption of plutonium on weathered rapakivi granite, YT5-2, in groundwater under aerobic conditions. Pu concentrations in mol/1. 44 DC 0.1 10 15 20 25 30 Fig. 24 Changes in the sorption of plutonium on altered rapakivi granite, YT5-3, in groundwater under aerobic conditions. Pu concentrations in mol/1. Under anaerobic conditions the amount of undissolved plutonium spike was between 29 and 83 %. There is no systematic pattern in the values. The sorption is fast. The Pu activities in solutions were at the detection limit and only lower limits could be derived. The amounts of dissolved plutonium affected the lower limit values of Rd: the lower the amount dissolved, the lower the minimum for Rd. The plutonium spike on the teflon strip remained undissolved in the samples of pure unfiltered groundwater. The E^, values (+1 - -118 mV) and pH values (7.19 - 8.37) were constant during the experiment (Appendix II, Table 6). 45 Table 17. The sorption (S%) and desorption (S.^%) and corresponding Rd values of plutonium in anaerobic conditions on rapakivi granite from groundwater. The contact time was 73 days in sorption and 49 days in desorption. 3 3 Rock Sample Undissolv. S% Rd (m /kg) sde% Rd,de(m /kg) % YT5-1 51 76±12 98±1 >0.54 99±1 >0.47 fresh 52 55±9 99±1 >1.0 100±l >0.92 53 29±5 100±l >1.6 100±l >1.4 YT5-2 54 83±13 99±1 >0.38 99±1 >0.33 weath. 55 62±10 98±1 >0.86 99±1 >0.75 56 72±12 98±1 >0.62 99±1 >0.55 YT5-3 57 27±4 100±l >1.7 99±1 >1.5 altered 58 61±10 100±l >0.89 99±1 >0.78 59 55±9 98±1 >1.0 99±1 >0.88 4.4.7. Technetium The fission product "Tc is a redox sensitive radionuclide. Under aerobic conditions the technetium occurs as pertechnetate, TcO4' and under reducing conditions the valence state +4 prevails. Tc(VII) is nearly non sorbing as TcO4" anion in oxic groundwater. Vandergraaf et al. /19/ have noticed that technetium is removed from anoxic solutions by iron oxides but not by minerals containing ferrous iron as an integral part of their crystal lattice. Haines et al. /20/ have demonstrated that the reaction between TcO4' and magnetite occurs via surface- mediated reduction to Tc(IV) and precipitation of TcO2 on the Fe3O4 surface /21/. Technetium was studied only under anaerobic conditions. In fact, we used technetium to confirm that reducing conditions prevailed. 46 Table 18. The sorption (S%) and desorption (8^%) and corresponding Rd values of technetium in anaerobic conditions on rapakivi granite. The contact time was 31 days in sorption and 49 days in desorption. 3 3 Rock Sample Undissolv. S% Rd (m /kg) sde% Rdde(m /kg) % YT5-1 21 4.210.2 9911 >0.88 10011 >0.55 fresh 22 4.210.2 9911 >0.87 10011 >0.56 23 3.910.2 99+1 >0.88 10011 >0.55 YT5-2 24 3.5+0.1 10011 >0.88 10011 >0.56 weath. 25 3.910.2 100+1 >0.87 10011 >0.56 26 3.510.2 9911 >1.2 9911 >0.55 YT5-3 27 3.610.2 10011 >0.88 10011 >0.56 altered 28 4.310.2 10011 >0.88 10011 >0.56 29 4.210.2 99+1 >0.87 10011 >0.56 Table 19. The sorption (S%) and desorption (Sde%) and corresponding Rd values of technetium in anaerobic conditions on rapakivi granite. The contact time was 77 days in sorption and 49 days in desorption. 3 3 Rock Sample Undissolv. S% Rd (m /kg) Sde% Rdde(m /kg) % YT5-1 30 <1 9911 >0.59 10011 >0.56 fresh 31 <1 9711 >0.58 10011 >0.55 32 <1 10011 >0.59 98+1 >0.58 YT5-2 33 <1 9511 >0.59 9911 >0.55 weath. 34 <1 100+1 >0.59 8711 >0.58 35 <1 100+1 >0.59 10011 >0.58 YT5-3 36 <1 9811 >0.59 99+1 >0.57 altered 37 <1 9811 >0.59 10011 >0.56 38 <1 10011 >0.59 95+1 >0.58 In sorption during the shorter contact time (31 days), 13% of the technetium from the teflon strip was dissolved when there was pure groundwater in the sample. When the contact time 47 was longer (77 days) the dissolved fraction was 94%. After desorption the activity of the precipitate of Fe-hydroxides was measured and about 30% of dissolved technetium was found in the precipitate. Although the measured values for E^ did not point to reducing conditions they were reducting enough for technetium and neptunium /14/ (Appendix II, Tables 1 and 3). 4.5. Diffusion experiments Figures 25 - 27 display curves of the mass flow of tritium, Ql/C, versus time. A stationary state for tritium was achieved in the rapakivi samples. Table 21 presents the ratio of cumulative breakthrough activity (A) to the total amount of tracer (\), diffusion coefficients De and Da and porosities (calculated and measured). 1.00 0.80 - esi 0.60 o o 0.40 - 0.20 " 40 60 60 100 120 140 160 160 Fig. 25 The cumulative mass flow of tritiated water for fresh rapakivi granite, YT5-1. A = sample 1, * = sample 2, 0 = sample 3. The time lag values are in Table 21. 48 0.80 0.60 CM E 0.40 0.20 0.00 20 40 60 80 100 120 140 160 180 time, d Fig. 26 The cumulative mass flow of tritiated water for weathered rapakivi granite, YT5-2. • = sample 4, o = sample 5, HI = sample 6. The time lag values are in Table 21. 0.12 0.10 CM 0.07 Esr Cm o w 0.05 0.02 - 0.00 20 40 60 60 100 120 140 160 180 Fig. 27 The cumulative mass flow of tritiated water for altered rapakivi granite, YT5-3. • = sample 7, v = sample 9. The time lag values are in Table 21. 49 Table 21. Diffusion characteristics of rapakivi granite. YT5-1 is fresh rapakivi and 1,2 and 3 are parallel samples. YT5-2 is weathered rapakivi and 4, 5 and 6 are parallel samples. YT5-3 is altered rapakivi and 7, 8 and 9 are parallel samples. Sample 8 began to leak after 20 days. Sample A/A. Time lag, L, e (V%) % d 10° m7s 10"" m7s % YT5-1-1 2.19 7.5 4.6 7.3 0.63 0.29 YT5-1-2 2.03 7.5 3.5 6.3 0.56 0.29 YT5-1-3 1.45 8.8 2.6 5.3 0.49 0.33 YT5-2-4 21.06 3.5 39 13 3.0 3.9 YT5-2-5 18.96 3.5 36 14 2.6 3.1 YT5-2-6 12.12 3.5 36 14 2.6 3.5 YT5-3-7 2.68 8.8 4.6 4.9 0.94 0.71 YT5-3-8 3.89 7.2 0.75 YT5-3-9 2.55 7.5 5.3 7.1 0.75 0.61 The measured, e, (sect.4.2) and calculated, DJDt, values of porosity in rapakivi granite are closely similar. The De values are ten times as great in weathered rapakivi granite as in fresh and altered rapakivi granite, and the Da values are twice as great. Apparently the weathered rapakivi granite was much more porous than the others. 50 5. SUMMARY OF THE RESULTS OF SORPTION AND DIFFUSION EXPERIMENTS The sorption material (rapakivi rock) was characterized with respect to cation exchange capacity, the amount of Fe-oxides and the porosity. The cation exchange capacity increased in order fresh, altered and weathered rock. The amount of amorphous Fe-oxides was less in weathered rock than in the more or less similar fresh and altered rock. The amount of crystalline Fe-oxides decreased in the order weathered, altered and fresh rock. The values of the volume porosity indicated that the weathered rock was clearly more porous than the altered and the fresh rock. The values of De for tritiated water increased in the order fresh, altered and weathered rock. At low concentration the sorption of cesium was similar in weathered and altered rock and weeker in fresh rock. When the concentration of cesium increased the sorption was the same for all rocks. In the case of radium the Rd values were mostly large. At the highest concentration of radium, 10'3 mol/1, the sorption was strongest for fresh rock. Much weaker sorption of radium was recorded for the weathered and altered rock. Under anaerobic conditions only 10% of the protactinium tracer dissolved. The sorption was similar on weathered and altered rock and greater on fresh rock. Uranium was studied only in aerobic conditions and there was no difference between the rapakivi rocks. The sorption was independent of concentration and was not quite reversible or else it was kinetically slow. In aerobic conditions the sorption of neptunium was not dependent on concentration and there was no difference between rapakivi rocks. In anaerobic conditions the sorption was high on all rocks and only the minimum for Rd could be determined. The sorption of plutonium was also high in aerobic conditions. There was no clear dependence of sorption on concentration at low concentrations (1013 - 10" mol/1), but the sorption was larger at concentration 10"9 mol/1 than at lower concentrations. Under anaerobic conditions the tracer was dissolved only partly, however. The sorption was high and only the minimum for Rd could be determined. The sorption of technetium was studied under anaerobic conditions, and also was of interest to check the reducing conditions in the glove box. The sorption was high and thus the system was reducing enough for technetium, as also concluded from the E^ and pH values. 51 6. COMPARISON WITH RESULTS FOR OTHER INVESTIGATION SITES ROCKS Sorption onto rapakivi granite is here compared with that onto rocks at the Posiva investigation sites at Olkiluoto, Kivetty and Romuvaara. The basis for the comparison is the cation exchange capacities of the rocks and the sorption of cesium, strontium and radium. As well the redox properties of the host rocks at Hastholmen are compared with those at the other investigation sites. 6.1. Cation exchange capacity The cation exchange capacities (CEC) of the rocks at the other sites /22/ were derived on the basis of mineral compositions and of literature CEC values for the minerals /23/. The CEC value for the unaltered rapakivi granite is about the same as for other unaltered granite rocks, largely because high capacity minerals are present in about the same amounts. The rapakivi granite at Hastholmen is sequentially layered rock of different degrees of alteration. The CEC value of the altered and weathered granite increases with the increasing amounts of clays and other high capacity alteration minerals. The CEC value of the altered rapakivi is slightly higher than that of the tonalites investigated and only slightly lower than that of mica gneisses. In addition to the high CEC capacity of the clays, they are favourable in sorption because, thanks to their small mineral grain size, the sorption sites are readily accessible. Rapakivi and some parts of the granites at Kivetty are red because of the hematite contained. The iron oxide minerals are efficient sorbents, especially for transition elements and certain actinides. Hydrothermal iron oxides are found in some tonalites, too, but are rare deep in the Olkiluoto mica gneiss. 6.2. Redox condition of the host rocks Theoretically the reduction capacity of a rock can be derived from its Fe(II) content. Mica gneisses and granodiorites of the bedrock at the investigation site contain clearly more of these minerals (biotite, chlorite, hornblende) than do the granites. On the other hand, it has 52 been shown that the Fe(II) bound to mineral structure is not necessarily readily available for oxidation. Small crystalline minerals (e.g. chlorite) may be more important reducers at least in the short run. The chlorite content of unaltered rapakivi is higher than the average in granites, and the chlorite contents of altered and weathered granites are even higher. Of the rocks studied, the Olkiluoto mica gneiss (YD1) has the highest chlorite content. 6.3. Ground waters The TDS (total dissolved solids) values for the Romuvaara and Kivetty investigation sites, TDS <1000 mg/1, indicate only fresh waters. Values of Cl 9200 mg/1 and TDS 35000 mg/1 have been measured in some saline waters at Olkiluoto. The TDS values at the bottom (792 m) of the KR1 hole at Olkiluoto (17000 - 30000 mg/1) indicate saline groundwater. In the Hastholmen rapakivi region, the maximum salinity measured at depths down to 200 m is about 10 000 mg/1 (TDS), and the waters are mainly brackish (1000 mg/1 < TDS < 10 000 mg/1). The pH values of the groundwaters in regions of acidic rocks at the investigation sites have been about the same, taking into consideration that the values include some inaccuracy due to the sampling technique used. The value for Hastholmen region does not deviate from the average. Redox electrode measurements at all the investigation sites have hinted at "reducing" groundwater/bedrock conditions. Reducing conditions have been most clearly demonstrated in high sulphide (Olkiluoto) and high Fe(II) (Hastholmen) waters. In conclusion, the pH/Eh values of the Hastholmen groundwater are about the same as in "reducing" waters in the other granitic region (Kivetty). 6.4. Sorption of cesium, strontium and radium Sorption of alkaline and earth-alkaline elements to silicate minerals is mainly by cation exchange and thus inversely proportional to ionic strength of the water. The Rd values of Sr 53 for Olkiluoto mica gneiss in 0LKR5 water (TDS 13000 mg/1) and for the Kivetty granite host rock system are 0.3 *10"3 m3/kg and 6 * 10"3 m3/kg. The corresponding values for Ra are 0.2 m3/kg and 1.5 m3/kg /6/. The values for Olkiluoto mica gneiss would be slightly lower in the OLKR1 water (TDS 23 000 mg/1) than in the OLKR5 water. The Rd values of Sr and Ra for the Hastholmen conditions were 0.6 - 1-0 * 10"3 m3/kg /22/ and 0.9 - 2.6 m3/kg (see sect. 4.4.2.). 3 The Rd values of cesium in the Hastholmen conditions were 0.1 m /kg for the unaltered rocks and 0.45 - 0.49 m3/kg for the altered and weathered rock (this work). The value for an unaltered Skoldvik mica gneiss containing the same amount of biotite as the Olkiluoto mica gneiss was 0.34 - 0.4 m3/kg /24/. Sorption of Cs to unaltered rock is nearly linearly proportional to biotite content of the rock /25/. It can be estimated that sorption of cesium to Olkiluoto mica gneiss in Olkiluoto water is about the same as to unaltered rapakivi in Hastholmen water. Sorption of cesium to rocks is much higher in Kivetty and Romuvaara 3 conditions than in saline waters. Rd values higher than 1.0 m /kg have been measured for Olkiluoto tonalite and rapakivi in fresh groundwater /25/. The Cs sorption capacity of rapakivi granite is the same as that for ultramafic hornblendite from Syyry. In conclusion, sorption of elements reacting mainly by cation exchange is higher in brackish Hastholmen groundwater conditions than in saline Olkiluoto groundwater conditions but lower than in Kivetty and Romuvaara fresh water conditions. 6.5. Sorption of redox-sensitive elements Sorption of neptunium and uranium on rocks is lower in aerobic saline waters containing carbonate than in fresh waters. The Rd values of uranium for Kivetty granodiorite in fresh water and for rapakivi in brackish Hastholmen water were 0.05 m3/kg and 0.001- 0.0015 m3/kg /26, sect. 4.4.4/. For mica gneisses in saline groundwaters of Olkiluoto and brackish groundwater of Hastholmen the values were 0.002 - 0.004 m3/kg and 0.006 - 0.020 m3/kg 1211. 54 The anaerobic groundwater conditions at Olkiluoto, Kivetty and Hastholmen are reducing for Np(V) and Tc(VII) /15, 28, this work/. At Romuvaara there were some technical difficulties in sampling of representative groundwater for anaerobic laboratory experiments. In an earlier experiment, however, U(VI) was in part reduced to U(IV) in R0-KR5 water /29/. The same was found for 0L-KR5 water /14/. In R0-KR5 water, Tc(VII) was in part reduced to Tc(IV), while in Hastholmen water the reduction to Tc(IV) was complete /28, this work/, which suggests the Hastholmen water to be more reducing. Relative to the conditions in the tonalite-, granodiorite areas at Romuvaara, the redox conditions at Hastholmen and Olkiluoto have been more clearly demonstrated to be reducing, especially at sampling depths where sulphide has been found. Alterations in the measured E,,- potentials due to technical problems with the Kivetty groundwater make it difficult to estimate the redox conditions. Sorption of neptunium, technetium and uranium to rapakivi granite under anaerobic, very low carbonate conditions is high and the same as that for Olkiluoto mica gneiss /14/. 6.6. Effective diffusion of water The effective diffusion of tritiated water in rapakivi is about the same as in the other rocks investigated. Diffusion of ionic species in rocks may be affected by anion exclusion and enhanced diffusion of cations called "surface diffusion". Both these processes are weaker in saline than in fresh waters. In this respect the host rocks at Olkiluoto and Hastholmen resemble each other, as do the host rocks at Kivetty and Romuvaara. 6.7. Conclusions In summary the sorption of the elements Cs, Sr, Ra, Np, Tc, U to rapakivi granite in Hastholmen bedrock is at least as high as that to host rock in the saline groundwater area of Olkiluoto. Sorption of cations is higher at Kivetty and Romuvaara, where groundwaters are fresh, than in the brackish groundwater area of Hastholmen. 55 7. REFERENCES 1. Chao, T.T., Use of partial dissolution techniques in geochemical exploration, Journal of Geochemical Exploration, 20 (1984) 101-135 2. Currie, L.A., Limits for Qualitative Detection and Quantitative Determination, Application to Radiochemistry, Analytical Chemistry, vol.40, no.3, March 1968, p 586 3. Crank J., The Mathematics of Diffusion, second edition, Oxford Science Publications, 1989 4. Barrer R., Diffusion in and through Solids, Cambridge University Press, 1951 5. Chabra, R., Pleysier, J., Cremers, A.: The measurement of the cation exchange capacity and exchangeable cations in soils: A new method. Proc.Int.Clay Conf. 1075, Applied Publishing Ltd, Wilmele, Illinois 60091, USA 6. Kulmala, S., Hakanen, M., Sorption of alkaline-earth elements Sr, Ba and Ra from groundwater on rocks from TVO investigation areas, Report YTJ-95-03 7. E.S.Pal'shin, B.F.Myasoedov and A.V.Davydov, Analytical Chemistry of Protactinium Humphrey Science Publishers, Ann Arbor-London, 1970 8. Wanner, H., Forest, I., eds., Chemical Thermodynamics of Uranium. Chemical thermodynamics 1, OECD Nuclear Energy Agency, 1992, North Holland. 9. Cotten, F.A., Wilkinson, G., Advanced Inorganic Chemistry. 3rd ed., New York 1972, Wiley Interscience 10. Ollila, K., Solubility of unirradiated UO2 fuel in aqueous solutions - comparison between experimental and calculated (EQ3/6) data. Helsinki 1995, Nuclear Waste Commission of Finnish Power Companies, Report YJT-95-14 11. Allard, B., Actinide solution equilibria and solubilities in geological systems. Stockholm 1983, Svensk Karnbranslesakerhet, SKB Technical Report 83-35 12. Allard, B., Anderson, K., Torstenfelt, B., The distribution coefficient concept and aspects on experimental distribution studies. Goteborg 1983, Svensk Karnbranslesakerhet, SKB Technical Report 83-63 13. Kipatsi, H., Sorption Behaviour of Long-lived Fission Products and Actinides in Clay and Rock. Goteborg 1983, Thesis, Department of Nuclear Chemistry, Chalmers University of Technology, Goteborg 14. Hakanen, M., Lindberg, A., Technetium, neptunium and uranium in simulated anaerobic groundwater conditions. Helsinki 1995, Nuclear Waste Commission of Finnish Power Companies, Report YJT-95-02 56 15. Allard, B., Olofsson, U. Torstenfelt, B., Kipatsi, H., Andersson, K., Sorption of actinides in well-defined oxidation states on geological media. Scientific Basis for Nuclear Waste Management V, New York 1982, W.Lutze (ed.) Mat.Res.Soc.Symp.Proc. 11, Elsevier Science Publishers Co., pp 775-782 16. Kim, J.I., The chemical behaviour of transuranium elements and barrier functions in natural aquifer systems. Scientific Basis for Nuclear Waste Management XVI. Mat.Res.Soc.Symp.Proc. 294. Pittsburg, Materials Research Society, pp 3-21 17. Penrose, W.R., Metta, D.N., Hylko, J.M. Rinckel, L.A., The reduction of plutonium(V) by aquatic sediments. J.Environ.Radioactivity, 5, pp 169-184, 1987 18. Kulmala, S., Hakanen, M., Review of the sorption of radionuclides on the bedrock of Hastholmen and on construction and backfill materials of a final repository for reactor wastes. Helsinki 1992, Nuclear Waste Commission of Finnish Power Companies, Report YJT-92-21 19. Vandergraaf, T.T., Ticknor, K.V., George, I.M., in Geological Behaviour of Radioactive Waste, G. Scott Barney ed. Am. Chem. Soc. Symp. Ser. 246, 24 (1984) 20. Haines, R.I., Owen, R.I., Vandergraaf, T.T., Nucl. J. Canada 1:1 (1987) 32-37 21. Cui, D., Eriksen, T.E., Reduction of Tc(VTI) and Np(V) in solution by ferrous iron. A laboratory study of homogeneous and heterogeneous redox processes. Stockholm 1996, Svensk Karnbranslehantering AB, SKB Technical Report 96-03 22. Hakanen, M., Holtta, P., Review of sorption and diffusion parameters for TVO- 92. Helsinki 1992, Nuclear Waste Commission of Finnish Power Companies, Report YJT-92-14. 23. Allard, B., Karlsson, M., Tullborg, E-L., Larson, S.A., Ion exchange capacities and surface areas of some major components and common fracture filling materials of igneous rock. Goteborg 1983, Svensk Karnbranslesakerhet, SKB Technical Report 83 24. Pinnioja, S., Hietanen, R., Alaluusua, M., Review of the sorption data of the main radionuclides in low and intermediate level nuclear wastes for Finnish bedrock. Helsinki 1986, Nuclear Waste Commission of Finnish Power Companies, Report YJT-86-02 (in Finnish with an English abstract) 25. Alaluusua, M., Hakanen, M., Lindberg, A., The sorption of cesium, strontium and cobalt on crushed rock produced by jaw crusher. Helsinki 1990, IVO/Nuclear Waste Studies, Work Report 90-2 (in Finnish) 26. Hakanen, M., Tuominen, S., Sorption and desorption experiments with crushed granite from Kivetty, University of Helsinki, Department of Radiochemistry, 1994, unpublished (in Finnish) 27. Kaukonen, V., Puukko, E., Hakanen, M., Lindberg, A., Diffusion of neptunium in Olkiluoto mica gneiss and pegmatite and Kivetty granite. TURVA-95-05 (in Finnish 57 with an English abstract) 28. Kulmala, S., Hakanen, M., Lindberg, A., Sorption of protactinium on rocks in groundwaters from Posiva investigation sites, Nuclear Waste Commission of Finnish Power Companies, Report POSIVA-96-12 29. Hakanen, M., Lindberg, A., Sorption of uranium on rocks in anaerobic groundwater. Helsinki 1992, Nuclear Waste Commission of Finnish Power Companies, Report YJT-92-25. LIST OF APPENDICES Appendix I. Groundwater chemistry data from Hastholmen, LPVA2 Appendix II. Measured E^ and pH values at the end of the experiments. 1 APPENDIX I Table 1. Analysed components of the groundwater, physical and chemical parameters, cations and anions. (LPVA2, 3 January 1996) Parameter Field measurements Lab.analyses (anal, after Lab.analyses (after I sampling) week equilibration and 0.22 \an filtration) PH 7.6 - 7.7 7.5 7.5 Conductivity, mS/m 1300 1300 Eh (Pt), mV -50 02, mg/1 0.005 Alkalinity, meq/1 1.25 1.2 Acidity, meq/1 0.28 0.07 Opacity, FTU 43 Colour, Pt mg/1 171 Paniculate matter, mg/1 not found KMnO4, mg/1 0.7 Tot. hardness, °dH 193 DOC, mg/1 0.85 SiO2, mg/1 9.4 9.4 Br, mg/1 17.6 17 F, mg/1 1.1 1.1 I, mg/1 0.071 PO4> mg/1 <0.01 <0.01 SO4, mg/1 550 510 SMI), mg/1 <0.01 Cl,mg/1 4900 5060 Al, mg/1 0.006 0.001 Ba, mg/1 <0.5 <0.5 Ca, mg/1 780 785 Fe,,,,, mg/1 5.8 (5.6onof) 0.08 Fe(II), mg/1 5.3 K, mg/1 29 29 Mg, mg/1 240 239 Mn, mg/1 3.1 3.1 Na, mg/1 2040 2080 Ni, mg/1 0.002 0.001 B, mg/1 0.25 0.20 Cs, mg/1 0.009 0.005 Li, mg/1 0.10 0.14 Sr, mg/1 6.1 6.0 Zr, mg/1 0.01 0.02 Table 2. Analysed isotopes and gases. 3 January 1996. Parameter Field measurements Lab.analyses (anal, after Lab.analyses (after 1 sampling) week equilibration and 0.22 Mm filtration) H-3, TU <7.2 U-238, mBq/1 (filtrate) 83 ±3 U-234/U-238 (filtrate) 2.12±0.10 U-238, mBq/1 0.17 ± 0.05 and <0.13 (membranes)* U-234/U-238 1.33 ± 0.62 and - (membranes)* 0-18, %o SMOW -8.22 H-2, %«, SMOW -67.2 H-2.ul/l not found He, nl/1 115 N2, MVI 17800 CO2, MVI 820 CO, uJ/1 not found C2H4, MI/1 0.12 CH4.ul/l 29 C2H6, nl/1 0.16 Dissolv.tot C02, mg/1 51 * The amount and quality of paniculate matter vary in membranes. The reliability of the analyses is estimated by charge balance calculations: E = [Cations(meq/1) - Anions (meq/l))/(Cations(meq/l)+ Anions(meq/1))] x 100 According to this the values of lab. analyses (both immediately after sampling and after one week equilibration) are reliable the charge balance errors are: -0.87% (after sampling) and -1.48% (after 1 week equilibration and filtration). Table 3. Analysed components of the groundwater, physical and chemical parameters, cations and anions. (LPVA2, 13 August 1996) Parameter Field measurements Lab.analyses (anal, after Lab.analyses (after 1 sampling) week equilibration and 0.22 urn filtration) PH 7.73 7.12 7.74 Conductivity, mS/m 1300 1450 1460 Eh (Pt), mV -143 02, mg/1 0.0011 Alkalinity, meq/1 1.4 1.3 Acidity, meq/1 0.2 0.17 Free CO2, mg/1 8.8 Aggressive C02, mg/1 2.42 Ammonium ion, mg/1 2.4 Opacity, FTU 55 Colour, Pt mg/1 210 Paniculate matter, mg/1 17 KMnO4, mg/1 1.5 Tot. hardness,°dH 171 DOC, mg/1 0.9 SiO2, mg/1 9.7 9.0 Nitrate NO3, mg/1 0.53 Br, mg/1 16 17 F, mg/1 1.1 1.1 I, mg/1 0.10 PO4, mg/1 <0.01 <0.01 SO4, mg/1 528 491 S(-II), mg/1 <0.01 Cl, mg/1 4890 4800 Al, mg/1 0.010 0.013 Ba, mg/1 <0.8 <0.8 Ca, mg/1 800 760 Fe^,, mg/1 4.7(5.3ono() 0.82 Fe(II), mg/1 5.0 K, mg/1 26.1 26.8 Mg, mg/1 240 230 Mn, mg/1 2.4 2.4 Na, mg/1 2080 1990 Ni, mg/1 0.12 0.12 B, mg/1 0.08 Cs, mg/1 0.040 0.034 Li, mg/1 0.05 0.04 Sr, mg/1 4.4 3.3 Zr, mg/1 <0.01 <0.01 Table 4. Analysed isotopes and gases. 13 August 1996. Parameter Field measurements Lab.analyses (anal, after Lab.analyses (after 1 sampling) week equilibration and 0.22 um filtration) H-3, TU <6.6 U-238, mBq/1 (filtrate) 86 ±4 U-234/U-238 (filtrate) 2.11 ± 0.15 U-238, mBq/1 <0.07 (membranes)* U-234/U-238 - (membranes)* 0-18, %» SMOW -8.1 H-2, %o SMOW -63.0 H-2, nl/1 not found He, nl/1 100 N2, ul/1 17500 C02, ul/1 2000 CO, ul/1 not found C2H4, ul/1 0.035 CH4, ul/1 25 C2H6, uJ/1 0.04 Dissolv.tot C02, mg/1 58.1 * The amount and quality of particulate matter vary in membranes. The reliability of the analyses is estimated by charge balance calculations: E = [Cations(meq/1) - Anions (meq/l))/(Cations(meq/l)+ Anions(meq/1))] x 100 According to this the values of lab. analyses (both immediately after sampling and after one week equilibration) are reliable, the charge balance errors are: 0.245% (after sampling) and -0.988% (after 1 week equilibration and filtration). APPENDIX II Table 1. pH values at the end of the sorption experiment of protactinium under aerobic conditions. Table 2. pH values at the end of the sorption experiment of uranium under aerobic conditions. Table 3. pH values at the end of the sorption experiment of neptunium under aerobic conditions. Table 4. pH values at the end of the sorption experiment of plutonium under aerobic conditions. Table 5. E,, and pH values at the end of the sorption and desorption experiments of protactinium under anaerobic conditions (contact times 45 d and 15 d). Table 6. E,, and pH values at the end of the sorption and desorption experiments of neptunium under anaerobic conditions (contact times 31 d and 49 d). Table 7. E,, and pH values at the end of the sorption and desorption experiments of neptunium under anaerobic conditions (contact times 77 d and 49 d). Table 8. E,, and pH values at the end of the sorption and desorption experiments of plutonium under anaerobic conditions (contact times 73 d and 49 d). Table 9. E^, and pH values at the end of the sorption and desorption experiments of technetium under anaerobic conditions (contact times 31 d and 49 d). Table 10. E,, and pH values at the end of the sorption and desorption experiments of technetium under anaerobic conditions (contact times 77 d and 49 d). Table 1. Table 2. pH values of the samples after protactinium pH values of the samples after uranium sorption, sorption, aerobic conditions, contact time 31 d. aerobic conditions, contact time 26 d. nayte pH sample PH YT5-1- 151 7.63 YT5-1- 101 7.77 152 7.61 102 7.88 153 7.69 103 7.84 154 7.59 104 7.84 155 7.70 105 7.88 156 7.65 106 7.79 157 7.63 107 7.77 158 7.81 108 7.82 109 7.69 YT5-2- 167 7.70 110 168 7.71 111 7.74 169 7.59 112 7.81 170 7.71 113 7.79 171 7.74 114 7.80 172 7.72 115 7.83 173 7.67 116 7.92 174 7.68 YT5-2- 117 7.80 118 7.98 YT5-3- 183 7.66 119 8.05 184 7.63 120 7.99 185 7.82 121 7.94 186 7.60 122 7.84 187 8.00 123 7.79 188 7.67 124 7.89 189 7.75 125 7.88 190 7.68 126 7.94 127 7.92 128 7.86 129 7.87 130 7.70 131 7.89 132 7.80 YT5-3- 133 7.78 134 7.87 135 7.64 136 7.73 137 7.82 138 7.62 139 7.83 140 7.78 141 7.84 142 7.81 143 7.78 144 7.89 145 7.79 7.88 146 7.62 147 7.75 148 Table 3. Table 4. pH values of the samples after neptunium sorption, pH values of the samples after aerobic conditions, contact time 40 d plutonium sorption, aerobic conditions, (Np cone. 10"9 ja 10~7 mol/1) contact time 21 d. sample pH YT5-1- 159 7.63 sample pH 160 7.65 YT5-1- 250 7.65 161 7.66 251 7.83 162 7.59 252 7.54 163 7.82 253 164 7.58 254 7.66 165 7.56 255 7.54 166 7.67 256 7.60 257 7.74 YT5-2- 175 7.83 258 7.29 176 7.71 259 7.30 177 7.71 260 7.65 178 7.93 261 179 7.60 YT5-2- 262 7.62 180 7.86 263 7.51 181 7.70 264 7.43 182 7.82 265 7.49 266 8.08 YT5-3- 191 7.94 267 7.77 192 7.77 268 7.89 193 7.78 269 7.28 194 7.57 270 7.86 195 7.81 271 8.00 196 7.94 272 7.71 197 7.75 273 7.80 198 7.94 YT5-3- 274 7.66 275 7.75 (cone. 10"13 mol/1) 276 8.01 277 7.68 YT5-1- 41 7.55 278 7.78 42 7.58 279 7.81 43 7.80 280 7.56 281 44 7.89 282 7.65 283 YT5-2- 53 7.83 7.33 284 7.83 54 7.81 285 55 7.80 7.74 56 7.85 YT5-3- 65 7.72 66 7.74 67 7.76 68 7.78 Table 5. Eh and pH values after sorption and desorption of protactinium, anaerobic conditions, contact time 45 d and 15 d. sorption desorption sample E, PH E* pH YT5-1-41 +14 7.48 +34 7.68 YT5-1-42 +7 7.48 +6 7.69 YT5-1-43 -76 7.80 -1 7.70 YT5-2-44 -49 7.33 +29 8.15 YT5-2-45 -37 7.37 +79 8.18 YT5-2-46 -11 7.36 +100 8.08 YT5-3-47 -42 7.16 +114 8.20 YT5-3-48 -49 7.25 +20 7.77 YT5-3-49 -35 7.25 +24 8.20 Table 6. Eh and pH values after sorption and desorption of neptunium, anaerobic conditions, contact time 31 d and 49 d. sorption desorption sample EH pH E* PH YT5-1-1 +54 7.95 -74 7.68 YT5-1-2 +62 7.94 -65 7.65 YT5-1-3 +68 7.99 -67 7.70 YT5-2-4 +174 8.10 -24 7.41 YT5-2-5 +122 7.71 -14 7.22 YT5-2-6 +104 7.80 -17 7.26 YT5-3-7 +64 8.03 -45 7.64 YT5-3-8 +172 8.20 -39 7.65 YT5-3-9 +41 7.81 -39 7.54 Table 7. E,, and pH values after sorption and desorption of neptunium, anaerobic conditions, contact time 77 d and 49 d. sorption desorption sample EH pH E; pH YT5-1-11 -65 7.80 -86 7.81 YT5-1-12 -65 7.76 -146 8.11 YT5-1-13 -69 7.66 -130 7.91 YT5-2-14 -42 7.40 -112 7.55 YT5-2-15 -28 7.35 -109 7.50 YT5-2-16 -34 7.22 -171 8.44 YT5-3-17 -61 7.76 -178 8.52 YT5-3-18 -40 7.80 -139 7.89 YT5-3-19 -41 7.61 -178 8.60 Table 8. E^ and pH values after sorption and desorption of plutonium, anaerobic conditions, contact time 73 d and 49 d. sorption desorption sample Eh PH EH pH YT5-1-51 -27 7.74 -106 7.71 YT5-1-52 -39 7.72 -114 7.79 YT5-1-53 -40 7.65 -109 7.68 YT5-2-54 -42 7.62 -86 7.43 YT5-2-55 +1 7.19 -82 7.33 YT5-2-56 -8 7.25 -73 7.39 YT5-3-57 -32 7.82 -118 7.65 YT5-3-58 -32 8.37 -73 7.70 YT5-3-59 -34 7.58 -109 7.53 Table 9. Eh and pH values after sorption and desorption of technetium, anaerobic conditions, contact time 31 d and 49 d. sorption desorption sample Eh pH EH pH YT5-1-21 +88 7.90 -51 7.73 YT5-1-22 +120 7.96 -74 8.11 YT5-1-23 +32 8.01 -63 7.64 YT5-2-24 +77 7.84 -75 8.38 YT5-2-25 +89 7.65 -31 7.20 YT5-2-26 +126 8.10 +3 7.35 YT5-3-27 +38 7.86 -35 7.57 YT5-3-28 +21 7.82 -45 8.31 YT5-3-29 +18 7.81 -49 7.65 Table 10. Eh and pH values after sorption and desorption of technetium, anaerobic conditions, contact time 77 d and 49 d. sorption desorption sample £„ PH E, PH YT5-1-31 -86 7.80 -89 7.77 YT5-1-32 -64 7.74 -121 7.78 YT5-1-33 -74 7.80 -157 8.09 YT5-2-34 -49 7.42 -130 8.36 YT5-2-35 -31 7.22 -164 8.46 YT5-2-36 +1 7.21 -112 7.46 YT5-3-37 -34 7.76 -118 7.72 YT5-3-38 -48 7.70 -129 7.69 YT5-3-39 -49 7.63 -161 8.11 LIST OF REPORTS 1 (4) LIST OF POSIVA REPORTS PUBLISHED IN 1996 POSIVA-96-01 Determination of U oxidation state in anoxic (N2) aqueous solutions method development and testing Kaija Ollila VTT Chemical Technology June 1996 ISBN 951-652-000-6 POSIVA-96-02 Fault plane solutions of microearthquakes in the Loviisa region in south-eastern Finland Jouni Saari IVO International Ltd Ragnar Slunga Forsvarets Forskningsanstalt, Stockhom, Sweden June 1996 ISBN 951-652-001-4 POSIVA-96-03 Thermal optimisation of the final disposal of spent nuclear fuel Heikki Raiko VTT Energia June 1996 (in Finnish) ISBN 951-652-002-2 POSIVA-96-04 On the origin and chemical evolution of groundwater at the Olkiluoto site Petteri Pitkanen Technical Research Centre of Finland Margit Snellman Imatran Voima Oy Ulla Vuorinen Technical Research Centre of Finland June 1996 ISBN 951-652-003-0 POSIVA-96-05 Seismic emissions induced by the excavations of the rock repository in Loviisa Jouni Saari IVO International Ltd June 1996 ISBN 951-652-004-9 POSIVA-96-06 Geochemical modelling study on the age and evolution of the groundwater at the Romuvaara site Petteri Pitkanen Technical Research Centre of Finland Margit Snellman Imatran Voima Oy Ulla Vuorinen, Hilkka Leino-Forsman Technical Research Centre of Finland September 1996 ISBN 951-652-005-7 LIST OF REPORTS 2(4) POSIVA-96-07 Boring of full scale deposition holes using a novel dry blind boring method Jorma Autio, Timo Kirkkomaki Saanio & Riekkola Consulting Engineers November 1996 ISBN 951-652-006-5 POSIVA-96-08 Production methods and costs of oxygen free copper canisters for nuclear waste disposal Harri Aalto, Hannu Rajainmaki, Lenni Laakso Outokumpu Poricopper Oy October 1996 ISBN 951-652-007-3 POSIVA-96-09 Characterization of the excavation disturbance caused by boring of the experimental full scale deposition holes in the Research Tunnel at Olkiluoto Jorma Autio Saanio & Riekkola Consulting Engineers December 1996 ISBN 951-652-008-1 POSIVA-96-10 Gamma and neutron dose rates on the outer surface of the nuclear waste disposal canisters Markku Anttila VTT Energy December 1996 ISBN951-652-009-X POSIVA-96-11 Criticality safety calculations for the nuclear waste disposal canisters Markku Anttila VTT Energy December 1996 ISBN 951-652-010-3 POSIVA-96-12 Assessment of alternative disposal concepts Jorma Autio, Timo Saanio, Pasi Tolppanen Saanio & Riekkola Consulting Engineers Heikki Raiko, Timo Vieno VTT Energy Jukka-Pekka Salo Posiva Oy December 1996 ISBN 951-652-011-1 POSIVA-96-13 Design report of the canister for nuclear fuel disposal Heikki Raiko VTT Energy Jukka-Pekka Salo Posiva Oy December 1996 ISBN 951 -652-012-X LIST OF REPORTS 3(4) POSIVA-96-14 Final disposal of spent nuclear fuel in the Finnish bedrock, technical research and development in the period 1993-1996 Posiva Oy December 1996 (in Finnish) ISBN 951-652-013-8 POSIVA-96-15 The Hyrkkola native copper mineralization as a natural analogue for copper canisters Nuria Marcos Helsinki University of Technology Laboratory of Engineering Geology and Geophysics October 1996 ISBN 951-652-014-6 POSIVA-96-16 Final disposal of spent fuel in the Finnish bedrock, scope and requirements for site specific safety analysis Posiva Oy December 1996 (in Finnish) ISBN 951-652-015-4 POSIVA-96-17 Interim report on safety assessment of spent fuel disposal TILA-96 Timo Vieno, Henrik Nordman VTT Energy December 1996 ISBN 951-652-016-2 POSIVA-96-18 Sorption of protactinium on rocks in groundwaters from Posiva investigation sites Seija Kulmala, Martti Hakanen University of Helsinki Department of Chemistry Radiochemistry laboratory Antero Lindberg Geological Survey of Finland December 1996 ISBN 951-652-017-0 POSIVA-96-19 Final disposal of spent fuel in the Finnish bedrock, detailed site investigations 1993-1996 Posiva Oy December 1996 (in Finnish) ISBN 951-652-018-9 POSIVA-96-20 Suitability of Hastholmen Loviisa for final disposal of spent fuel - Preliminary study Posiva Oy December 1996 (in Finnish) ISBN 951-652-019-7 LIST OF REPORTS 4(4) POSIVA-96-21 Hydrogeochemistry of deep groundwaters of mafic and ultramafic rocks in Finland Timo Ruskeeniemi, Runar Blomqvist, Antero Lindberg, Lasse Ahonen Geological Survey of Finland Shaun Frape University of Waterloo December 1996 ISBN 951-652-020-0 POSIVA-96-22 Helium gas methods for rock characteristics and matrix diffusion Juhani Hartikainen, Kari Hartikainen University of Jyvaskyla, Department of Physics Aimo Hautojarvi VTT Energy Kalle Kuoppamaki, Jussi Timonen University of Jyvaskyla, Department of Physics December 1996 ISBN 951-652-021-9 POSIVA-96-23 Sorption of cesium, radium, protactinium, uranium, neptunium and plutonium on Rapakivi granite Tuula Huitti Martti Hakanen University of Helsinki Antero Lindberg Geological Survey of Finland December 1996 ISBN-951-652-022-7