2009 Report to Government on National Research and

properties for certain applications, such as grouting where water-rock
interactions at higher pH would have detrimental effects
• It is important <strong>to</strong> identify which of the possible problems that have been
highlighted by experimental and theoretical investigations would actually be
encountered in real reposi<strong>to</strong>ry environments.
A.81 Most investigations of the leaching behaviour of vitrified HLW have considered
natural groundwaters, rather than the highly alkaline groundwaters that could be
present in a co-disposal situation. As a result, there are significant uncertainties
about the reactivity of borosilicate glasses in these circumstances. Whether
radionuclides are immobilised through mineral precipitation or rendered mobile
and then transported in alkaline but also saline fluids are issues that also need
intensive study (Hoskin & Burns, 2003; Grambow, 2006; Geisler et al., 2007;
Putnis & Geisler, 2007). UK glasses are more reactive than the French
equivalents due <strong>to</strong> their high Mg content (Abraitis et al., 2000), illustrating the
need for caution in using experimental data from overseas. There is a clear need
for further experiments on borosilicate glass stability in the presence of complex
alkaline and saline fluids under both static and dynamic (i.e. with fluid flow)
conditions.
A.82 Corrosion of metals will generate gas in both the ILW/LLW and HLW/spent fuel
parts of a co-located GDF. However, the amounts of gas that will be produced in
the ILW/LLW part are greater because there will be more metallic waste
containers, much ILW consists of metals, and some ILW is organic and will
degrade <strong>to</strong> form gases (paras A.59-A.65). There is therefore an issue of whether
gas generated in the ILW/LLW part of a facility could affect groundwater
movement in the HLW/spent fuel part of a facility.
GDF Design
A.83 The process of GDF design is discussed in the CoRWM report <strong>to</strong> <strong>Government</strong> on
geological disposal (CoRWM doc. 2550). In that report CoRWM emphasised the
need <strong>to</strong> consider a wide range of disposal concepts, constructed using various
techniques, at depths ranging from about 200m <strong>to</strong> more than 1km. R&D may be
required <strong>to</strong> enable the options (including co-location) <strong>to</strong> be evaluated and
compared at the conceptual level.
A.84 Options for GDF designs cannot be developed in any detail until potential sites
have been identified and assessment of these sites has begun. An integrated
process of GDF design, site assessment and safety case development work is
then required <strong>to</strong> provide input <strong>to</strong> design and siting decisions (CoRWM doc. 2550).
R&D requirements will be identified in the course of this process. In the
meantime, useful studies could be undertaken <strong>to</strong> define the influence that the
form of the underground openings and excavation and support methods have on
design. In relation <strong>to</strong> tunnel and shaft design the quality of the rock mass and the
in situ stress conditions will greatly influence the size, shape, support
requirements and the proximity of openings <strong>to</strong> one another. It is considered that
research is required in the following areas:
• Response of the rock mass <strong>to</strong> excavation and extent of any disturbance of
the rock adjacent <strong>to</strong> underground openings.
CoRWM Document 2543, Oc<strong>to</strong>ber <strong>2009</strong> Page 120 of 151