BOA and Safety Functions of Buffer. Markus Olin, VTT

Transcription

1 BOA and Safety Functions of Buffer Markus Olin, VTT

2 2 Definitions Physicochemical reality (PC): final disposal conditions, sodium bentonite Evolving external conditions, material properties and processes changing them Bentonite buffer must fulfil some safety functions (SF): closing of spent fuel, beneficial chemical conditions, mechanical protection Transport by diffusion only, no corrosion of copper, dampening of dislocations Predictable conditions Several research methods are available (RM): main division to experimental, theoretical and computational methods g

3 3 Hierarchy Purpose-Structure-State-Performance Purpose is set by SF, which is sub entity of PA-analysis SF defines also part of structure for the buffer research, however mainly without couplings Most part of structure is obtained understanding of PC State of work varies, and those of highest importance may be not be best known and must studied There are also differences in performance of sub systems: in some cases present level of knowledge is not performing very well compared to needs set by SF

4 4 f d LS-TUPER Very limited set of parameters and processes BOA Performance and safety analysis: prediction evolution estimation of RN release Selected set of quantities guarantying beneficial properties and set of processes altering them Safety functions: protect canister, and limit and delay release of RN Physicochemical reality: repository conditions and bentonite buffer

5 5 Structure & processes vs. PA Safety functions: protect canister, and limit and delay release of RN Beneficial properties of Long term stability: Alteration, dissolution, hardening Effects of accessory minerals Number and distribution of water layers Pore size distribution Corrosion of canister very slow Differences Na vs. Ca Microbial activity Formation and transport of colloids RN transport limited to diffusion, sorption High enough density Transport limited by diffusion Montmorillonite losses: erosion dissolution homogenisation Deformations and stresses, friction Cation exchange and diffusion Alteration of Dissolution of Transport limited by diffusion Ductility -chemical hardening Canister survives during dislocations Effects of accessory minerals

6 s Safety functions: protect canister, and limit and delay release of RN Processes related to these shown below Boxes of blue colour = BOA Boxes of green colour = other issues Boxes of yellow colour = safety functions Canister survives in dislocations Deformations and stresses, friction self healing Ductility - chemical hardening Microbial activity RN Alteration of Corroding agents in and products out Dissolution of RN transport limited to diffusion, sorption Cation exchange and diffusion Formation and transport of colloids Montmorillonite losses by erosion Homogenisation

7 7 Stucture related to processes Boxes of blue colour = BOA Boxes of green colour = other issues Boxes of yellow colour = safety functions Dissolution of Montmorillonite losses by erosion Homogenisation Alteration of Montmorillo nite: solid part Cations (Na, Ca, etc) Cation exchange and diffusion Bound water: properties and amount Free water pores: amount and distribution Ductility - chemical hardening Microbial activity Deformations and stresses, friction self healing Diffusion Formation and transport of colloids Corroding agents in and products out RN transport limited to diffusion, sorption Canister survives in dislocations

8 8 P: MPa Conditions T: o C S: I: 0.01 mm 1 M 1 mg/l 100 g/l Na-Ca-Cl d : kg/m 3

9 9 Scales and bentonite characteristics Colloidal size Pore size Laboratory Small scale Pilot scale Repository scale Relative amount of Cationic form of Accessory minerals Grain size, initial water content

10 10 Structure and processes Number and distribution of water layers Pores: free, interlamellar, diffuse layer Pore size distribution vs. density Microstructure of bentonite Differences between Na and Ca (K, Mg too) Colloids: formation and transport by Processes of bentonite Microbes: analysis and effects Solubility of Deformations and stresses, friction Effects of accessory minerals Cation exchange and diffusion

11 11 Experimental methods NMR XRD SAXS Number and distribution of water layers Nano tomography Pores: free, interlamellar, diffuse layer Micro tomography Pore size distribution vs. density Colloids: formation and transport by Microstructure of bentonite Processes of bentonite Differences between Na and Ca (K, Mg too) Microbes: analysis and effects Batch exp. Loose bentonite ICP-MS analysis Solubility of Basic characterisation Effects of accessory minerals Cation exchange and diffusion Deformations and stresses, friction Mechanical properties Coupled experiments

12 12 Modelling methods and tools Molecular: AccelRys Number and distribution of water layers Molecular dynamics Pores: free, interlamellar, diffuse layer THC Pore size distribution vs. density Microstructure of bentonite Differences between Na and Ca (K, Mg too) Colloids DLVO Colloids: formation and transport by Processes of bentonite Microbes: analysis and effects THM Numerrin Solubility of Deformations and stresses, friction THMC(B) Numerrin THC Geochemist s Workbench Effects of accessory minerals Cation exchange and diffusion THMC COMSOL THC TOUGHREACT COMSOL Multiphysics

13 13 Goals THMC(B)-model, which good enough over predicted conditions Concept based on experimental observations All needed data can be measured Consistent model mathematics Implementation possible by present computing resources Karakterisointi- ja analyysimenetelmät, joilla voidaan tehdä tarvittavat määritykset Riittävän tarkka ja luotettava kokeellinen määritys Prosessikokeet, jotka tukevat mallinnusta ja joiden toteutusta auttavat sopivat karakterisointi- ja analyysimenetelmät Tarkoin valittu joukko kokeita ja testejä Tavoitteena EI ole ratkaista joukko ongelmia, vaan tuottaa toimintamalli, jolla bentoniittia voidaan tutkia tehokkaasti

14 14 VTT luo teknologiasta liiketoimintaa