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<j values of cesium, radium, protactinium, uranium, neptunium and plutonium were determined and diffusion of water in the rapakivi was investigated. 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.