2009 Report to Government on National Research and

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Figure 6. Adsorption Processes Source: DePaolo and Orr, 2008. A.57 Further work is needed <strong>to</strong> understand and model radionuclide migration <strong>to</strong> a level that captures the uncertainty over future behaviour so that migration can be represented appropriately in a safety case. In particular, more understanding is required of: • radionuclide physico-chemical form (speciation) • the spatial variability, temporal evolution and reactivity of mineral surfaces • upscaling molecular level models <strong>to</strong> estimate bulk chemical properties, both thermodynamic and kinetic, and transport over spatial scales from nanometres <strong>to</strong> hundreds of metres. A.58 These issues are discussed in detail in Boxes 7-9. CoRWM Document 2543, Oc<strong>to</strong>ber <strong>2009</strong> Page 112 of 151
Box 7. Radionuclide Speciation Many of the elements which are important in geological disposal (e.g. iodine, technetium, uranium, neptunium, plu<strong>to</strong>nium) can access different oxidation states with very different chemical properties, and hence may be present as different complexes with bound water and other ligands (Runde, 2000). The chemical form will control solubility and subsequent sorption. In the extreme (carbon-14), speciation changes may even affect whether a radionuclide is present in the solid, liquid or gas phases. Chemical speciation is also influenced by biological processes, either directly through entrainment of a radionuclide in active metabolic processes, or indirectly, through reaction of a radionuclide with a biogenic chemical species. A chemical reaction will only proceed when the system as a whole moves from a higher <strong>to</strong> a lower energy. A reaction which proceeds rapidly <strong>to</strong> the lower energy state is said <strong>to</strong> be under “thermodynamic control”. However, the existence of an energetic driving force does not necessarily mean that the reaction will occur <strong>to</strong> any significant extent because the reaction may proceed slowly. In such a case, the reaction is said <strong>to</strong> be under “kinetic control”. It is relatively easy <strong>to</strong> predict the thermodynamic end state of a reaction, but many reactions which are important in geological disposal, for example reaction of rocks with alkaline fluids, or the crystallisation of minerals, are kinetically controlled and, because the progress of such a reaction will depend on the time elapsed, it is much harder <strong>to</strong> predict the behaviour of such systems. Several key processes relevant <strong>to</strong> geological disposal are in practice under kinetic control and some, such as colloid-mediated transport, represent major uncertainties in establishing the GDF safety case (King et al. 2001). Biological effects can affect the path of a reaction; for example, CO2 is thermodynamically unstable in strongly reducing conditions but the kinetics of chemical reduction <strong>to</strong> CH4 are so slow that the reaction essentially does not occur. However, biotransformation by some micro-organisms of CO2 <strong>to</strong> CH4 is efficient, so a system with appropriate biological activity will contain CH4, whereas one which cannot support bioreduction will contain CO2. Box 8. Mineral Surface Reactivity At the molecular level, the surfaces of minerals are very reactive through a range of different mechanisms. Some, such as the feldspar surface, undergo a series of pH-dependent leaching, dissolution and precipitation reactions, leading <strong>to</strong> the formation of altered and secondary layers on the surface (Chardon et al., 2006) while others interact through dissolution and reprecipitation, which leads <strong>to</strong> overturn of the surface (Morse & Arvidson, 2002). These surfaces interact with solutes by a range of processes, including inner- and outer-sphere surface complex formation, surface precipitation and other poorly defined interactions. Although they differ in the detail of their mechanisms, and this has important implications for mobility, these are often collectively referred <strong>to</strong> as “sorption” reactions (e.g. Brown et al., 2007). CoRWM Document 2543, Oc<strong>to</strong>ber <strong>2009</strong> Page 113 of 151
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Committee on Radioactive Waste Mana
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Finland ...........................
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Geosphere Characterisation ........
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EXECUTIVE SUMMARY 1. CoRWM’s remi
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odies would need to</strong
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disseminate and assimilate its resu
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1.3 CoRWM’s Work Programme for 20
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1.11 The R&D requirements for the l
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2. ESTABLISHING R&D REQUIREMENTS Wh
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adioactive waste management facilit
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should mitigate the risks of findin
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there is no unwarranted repetition
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safety case development, the overal
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Table 1. Approximate annual levels
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Figure 1. Structure of UK R&D provi
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NDA R&D for Geological Disposal 3.1
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3.27 The purpose of NNL can be summ
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identified the research required an
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submitted to RCEP
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Box 1. Research Council Funded Univ
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3.62 BGS is conducting three projec
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3.70 In the current FP7 programme (
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3.77 RCEP noted that there was a la
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sectors: land disp
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eyond those that RWMD intends <stro
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Box 2. USDOE 2006 Workshop R&D Issu
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3.111 Fundamental and applied resea
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France 3.122 There are six major gr
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and in concert with Forpro is desig
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• encourage the transfer and pres
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Page 63 and 64: 4. R&D SKILLS TO SUPPORT THE MRWS P
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Page 77 and 78: Retention of Skills 4.48 It has bee
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Page 81 and 82: purchase of equipment. In addition,
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Page 93 and 94: 7. CONCLUSIONS AND RECOMMENDATIONS
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Page 99 and 100: Current and Planned R&D for ILW A.5
Page 101 and 102: wasteform integrity at end of s<str
Page 103 and 104: Magnox Fuel A.20 Magnox fuel consis
Page 105 and 106: capability exists in the UK for doi
Page 107 and 108: purpose-built building. The former
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Page 111: through all these. The nature of th
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Page 117 and 118: than that for uranium-235. Likewise
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Page 121 and 122: • Long-term stability and perform
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Page 127 and 128: Number Title 2500 Interim S
Page 129 and 130: EPSRC, 2009. Grant
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Page 133 and 134: Skomurski FN, Ewing RC, Rohl AL, Ga
Page 135 and 136: Co-location Disposal of “high lev
Page 137 and 138: Geosphere Solid portion of the eart
Page 139 and 140: Packaging Placing waste int
Page 141 and 142: Stillage A metal frame used <strong
Page 143 and 144: BNGSL British Nuclear Group Sellafi
Page 145 and 146: FP Framework Programme (of the Euro
Page 147 and 148: MOX mixed oxide fuel (contains uran
Page 149 and 150: RS Royal Society RSC Royal Society
Page 151: ACKNOWLEDGEMENTS Leadership in the
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2009 Report to Government on National Research and

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