glass – long-term corrosion/dissolution rates, secondary product identification.

metal – corrosion products during the short-term oxic (operational) phase and longterm anoxic (post-closure) phase, pitting corrosion rates

bentonite – potential alteration in brines and hyperalkaline leachates, high-temperature effects, long-term durability to low-alkali cement leachates

cements and concretes – long-term leaching behaviour, degree of carbonation, degradation, long-term durability novel formulations (including low alkali cements).

As much of the EBS data are fairly generic, such work is an ideal area for international collaboration and could be supported by, e.g., the EU or the IAEA. Ideally, all such tests would be part of an integrated programme which would include the in situ tests, laboratory and modelling work and natural analogue studies, as this would allow identification of the significant mechanisms and processes on all scales (temporally and physically). Additionally, such an approach would lead to a better understanding of the areas of concern by a wider spectrum of shareholders by providing demonstrations of the key processes over the relevant timescales (see also comments in, e.g., Alexander et al., 1998).

10.3.7. Future SA code development

As noted in Chapter 6, performance/safety assessors are often wary about using the word ‘‘prediction’’ to describe evaluations of the performance and levels of safety provided by a repository (see also comments in Savage, 1995). This is because there is a danger that the word may be misinterpreted as meaning precise predictions of, e.g., the actual release of radioactivity from the repository, the actual rate at which radioactivity from the repository enters the biosphere or radiation doses received by human populations living in the future. In fact, doses and risks calculated on the basis of stylised approaches and simplified models should be interpreted as illustrations based on agreed sets of assumptions for particular scenarios and well-defined, but not necessarily realistic, model assumptions, and not as actual measures of future health detriments and risks (ICRP, 2000).

It may be that, if it appears that an analysis will give results near to or exceeding regulatory guidelines, then effort is spent in developing and testing more realistic models and databases that reduce the level of conservatism, thereby reducing the calculated doses or risks to levels that are well below the relevant guidelines. Future SAs may also use Bayesian logic to allow use of prior knowledge to help assess the likely implications of new design or host rock options (see, e.g., Curtis and Wood, 2004).

Finally, development of new SA codes which would provide more ‘‘transparent’’ (to all stakeholders) assessments have been discussed within the radwaste industry for the last decade. To date, little has been achieved but, as more programmes move towards repository implementation, it seems likely that the pressure to make the black magic of repository SA more accessible (and therefore more understandable) to stakeholders will increase. Indeed, there is an argument that such an opening up of SA would help countermand the ‘‘anti-science/relativist’’ approach to dealing with radwaste which Baverstock and Ball (2005) have accused the UK’s CoRWM of utilising in its assessment of the way forward for the UK radwaste industry.

A safety case needs to be presented in a style that is understandable and useful to its intended audience, taking account of their interests, concerns and level of technical