CEMENTED WASTEFORMS FOR DISPOSAL OF NUCLEAR WASTES

Intermediate and low level nuclear wastes (ILW and LLW) are routinely mixed with composite cement systems to prepare a waste form suitable for long-term storage or disposal. These composite waste forms are currently based around the use of Portland cement with high replacement levels of supplementary cementing materials (SCMs) such as blast furnace slag (BFS) or pulverised fuel ash (PFA). These grout formulations have been chosen to minimise the temperature rise in large volumes (up to 3m3) to avoid water loss and thermal stresses within the waste form and to provide highly fluid grouts. The use of these systems is intended to provide immobilisation of mobile species likely to be present in the wastes, as well as encapsulation of wastes such as metallic Al and particulate slurries.The large replacement volumes of SCMs produce hydrated cement matrices where the microstructure and compounds formed exhibit some differences to these found with the normal hydrated cement pastes. Some unusual effects can occur in the matrices during immobilisation of some of the systems we are examining, influencing the microstructure, particularly of the calcium silicate hydrate. Some of these effects will be described in the context of microstructure changes and the potential effects on durability. Not all wastes can successfully be made into durable waste forms with Portland cement and alternative cementing systems are being considered. Initial data on some of these systems will also be presented.

• ABSTRACT

• INTRODUCTION

• CONVENTIONAL CALCIUM SILICATE CEMENTING SYSTEMS

• ALTERNATIVE CEMENT SYSTEMS

• CONCLUDING REMARKS

• ACKNOWLEDGEMENTS

• REFERENCES