The Influence of Hyper-Alkaline Leachate on a Generic Host Rock Composition for a Nuclear Waste Repository: Experimental Assessment and Modelling of Novel Variable Porosity and Surface Area

Abstract Deep geological disposal is the preferred solution for long-term storage of radioactive waste in many countries. In a deep repository, cementitious materials are widely used structure and buffer/backfill repository stabilisation hazardous materials. The cement acts as physical barrier also contributes chemically to containment by buffering groundwater high pH, limiting solubility radionuclides. This paper describes an experimental modelling study which evaluates geochemical interaction between young leachate (YCL, pH = 13) generic hard rock (in this case Hollington sandstone, representing ‘hard’ host rock) during permeation with leachate, it drives mineralogical changes system. One-dimensional reactive transport was modelled using mixing cell approach within PHREEQC code identify essential parameters understand scale up effect variations these on observed processes. focused effects variable porosity, surface area pore volume improving alteration system compared conventional models that assume constant values properties. numerical results showed injected hyper-alkaline sandstone sample series reactions. main processes were dissolution quartz, kaolinite k-feldspar coupled precipitation calcium silicate hydrate gel tobermorite-14A (C–S–H), prehnite (hydrated silicate), saponite-Mg (smectite clay) mesolite (Na–Ca zeolite). simulation overall porosity increased primary minerals dissolve no stable secondary C–S–H /C–A–S–H phases predicted. scenario provides better fitting data more detailed trends chemistry change column. time number moles precipitated improved related greater exposure YCL. Article Highlights drop calcium, aluminium concentrations mainly due formation zeolite phases. had minimal values, controlled initial fluid chemistry.