The Modelling of Gas Migration through Compacted Bentonite Buffers in Radioactive Waste Repositories: the Work of the GA
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7KH0RGHOOLQJRI*DV0LJUDWLRQWKURXJK&RPSDFWHG%HQWRQLWH%XIIHUVLQ5DGLRDFWLYH :DVWH5HSRVLWRULHV WKH:RUNRIWKH*$0%,7&OXE William R Rodwell, Andrew R Hoch and Ben T Swift Serco Assurance, 150 Harwell IBC, Didcot, Oxfordshire OX11 0QJ, UK $%675$&7 Use of compacted bentonite buffers is frequently planned in radioactive waste repositories to isolate waste canisters from the geological environment. When gas is generated from the wastes or their containers, it will need to migrate through the bentonite if pressure rises local to the canisters are to be avoided. Assessment of the effect of gas produced from waste canisters in bentonite buffers requires both experimental data on and models of gas migration through initially water-saturated bentonite. Several different approaches to modelling gas migration through bentonite are described. Some example comparison of model results with experimental data are provided, and some general discussion about the modelling approaches is offered. ,1752'8&7,21 The use is widely proposed of bentonite clay as a buffer material around waste packages in radioactive waste repositories, particularly repositories for high-level waste and spent fuel. The swelling properties of bentonite clay make it an effective sealing material and its very low water permeability and high sorption capacity for many radionuclides provide barriers to radionuclide transport. In many circumstances, hydrogen gas will be produced from corrosion in or from the surface of waste containers in excess of the amount that can be transported by diffusion, presenting the possibility that the low permeability bentonite buffer will then restrict the escape of this gas, causing a possible rise in pressure. There is then concern that this might lead to rupturing of the bentonite buffer, reducing its subsequent effectiveness as a barrier to radionuclide transport, although there are experimental results indicating that gas flow paths created through bentonite buffer material will seal when they are reinvaded by water. Experimental work is being carried out to elucidate and confirm the mechanisms and characteristics of gas migration through water-saturated compacted bentonite, but a need has also been recognised for the capability to model gas migration through compacted bentonite. A consortium of radioactive waste disposal agencies, the GAMBIT Club, has been supporting efforts to develop an appropriate model of gas migration through bentonite, with the objectives that the model (a) should adequately represent the principal features observed in experiments of gas migration through compacted bentonite, (b) can be used to analyse and interpret experimental results, and (c) will provide the basis of a model that can be used to assess pressure build up and escape of hydrogen gas through bentonite around waste canisters in a repository. This paper provides an overview of the model development work of the GAMBIT Club. (;3(5,0(17$/'$7$21*$60,*5$7,21,1%(1721,7( Experimental data on gas migration in bentonite has been re
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