Nuclear Research Institute Řež plc Ústav jaderného výzkumu Řež a.s. 1 Development of waste matrices for immobilization of problematic waste from Czech nuclear power plants RCM on CRP „Behaviour of Cementitious Materials in Multipurpose Packaging for Transportation, Long Term Storage and Disposal Bucharest, 24– 28 November 2008 Petr Večerník, Monika Kiselová, Antonín Vokál

Nuclear Research Institute Řež plc 2 Main objectives of the project 1)Optimalization of cement composition and testing of new matrices for immobilization of ion-exchange resins, sludge and oils from Czech Nuclear Power Plants Dukovany and Temelín 2)Understanding of leaching mechanisms from cement matrices to be able to get data for advanced performance assessment codes and waste acceptance criteria (WAC) derivation 3)Starting activities for research of cementitious materials for Deep Geological Repository

Nuclear Research Institute Řež plc 3 Main streams of problematic waste in Czech NPPs Wet  Ion-exchangers  Sludge (often mixed with ion-exchange resins)  Oils Solid  Waste exceeding limits for near-surface repositories – stored  DGR Dukovany near surface respository Planned Deep Geological Repository

Nuclear Research Institute Řež plc 4 Waste Acceptance Criteria for Dukovany repository  Leaching resistance of waste forms with activity higher than 2 x 10 7 Bq  4 % after 48 hours (test RAWRA K001b)  Compressive strength  Cement – 5 MPa  Geopolymer – 10 MPa

Nuclear Research Institute Řež plc 5 Model waste Organic spent ion- exchangers simulated by saturation of new ion- exchange resins (Purolite A-400 MB OH and Purolite C-100 H) Ion-exchangers were saturated from 90 % and the ratio of cationic to anionic resins was set to the ratio 2:1. Samples were doped with Cs-137

Nuclear Research Institute Řež plc 6 Cemented samples Cements  Portland cement CEM I 52,5 R  Portland cement with slag CEM II/A –S 42,5 R Additives  Plastificators (Addiment FM 935)  Fillers (silica, ash)

Nuclear Research Institute Řež plc 7 Selected procedure 1) Mixing 5 minutes of water with plastificator 2) Mixing 10 minutes cement with filler 3) 28 days curing before testing

Nuclear Research Institute Řež plc 8 Cement compositions  Commercial cement with slag (CEM II/A-S 42,5 R of Lafarge Company) seems to be the most suitable basic materials both for cementation of spent ion- exchangers and sludge.  High amount of silica (> 20 %) and water reducing admixtures (plasticizers) (about 10 %) is needed to achieve required properties, namely to withstand immersion test and to meet compression strength higher then 5 MPa.  The total content of water must be less then 30 %

Nuclear Research Institute Řež plc 9 Composition of mixture for experiments

Nuclear Research Institute Řež plc 10 Samples for experiments

Nuclear Research Institute Řež plc 11 Qualification tests of cement mixtures Compression strength (5 MPa cement, 10 MPa geopolymers) Leaching characteristics (ANSI/ANS 16.1)

Nuclear Research Institute Řež plc 12 WAC derivation from PAs Data obtained from leaching experiments, such as ASNSI/ANS 16.1 are not sufficient for performance assessment purposes and WAC derivation. For advanced transport models following data are needed: 1) Effective diffusion coefficient (D e ) 2) Sorption coefficients 3) Formation factors 4) Solubility limits

Nuclear Research Institute Řež plc 13 Evaluation methods Batch sorption experiments Through diffusion experiments Electromigration experiments D a – Apparent diffusion coefficient D e – Effective diffusion coefficients  - Porosity  d - Dry density K d – Distribution coefficient F f – Geometric (tortuosity) factor f s – available porosity factor

Nuclear Research Institute Řež plc 14 Sorption of 137 Cs on cement

Nuclear Research Institute Řež plc 15 Diffusion experiments Tracers  3 H  125 I Through diffusion cell D a = 1.2 – 1.6 x m 2 s -1 D e = 2.6 – 4.6 x m 2 s -1 D W = 2.4 x m 2 s -1 Experiments with 125 I are still running 3 H experiments

Nuclear Research Institute Řež plc 16 Electromigration experiments Through electromigration method (TEM)

Nuclear Research Institute Řež plc 17  p – saturated sample conductivity,  w – electrolyte conductivity Electromigration experiments Electromigratory flux (N  ):  e – ion mobility, U – potential, C H – high concentration in reservoir, C L – low concentration in reservoir, C p concentration in pore water F – Faraday constant, z – charge number

Nuclear Research Institute Řež plc 18 Electromigration experiments Advantages of TEM -much faster than classical through diffusion method -not limited sample dimensions as in through diffusion Disadvantages of TEM / be careful of - possible pH changes due to electrolysis - possible changes of solution composition - possible changes in rock sample Advantages of TEM

Nuclear Research Institute Řež plc 19 Preliminary results for cesium D a from leaching experiment = 3 x m 2 /s D a from sorption and diffusion experiments = 1 x m 2 /s (calculated from equation D e from tricium through diffusion experiments = 3.6 x m 2 /s K d = 2 x m 3 /kg  = 0.15  = 2700 kg/m 3

Nuclear Research Institute Řež plc 20 Further plans Finish through diffusion and electromigration experiments to acquire data for modelling and to get deeper understanding of transport of radionuclides in cementitios materials To start experiments for developing cementitios materials for use in DGR  low pH  low water permeability  good gas permeability  good mechanical properties To start ageing and permeability measurements of cementitious materials on special prepared equipment