(368a) The Investigation of Aluminium Wastes Encapsulated In the Individual Phases of Ordinary Portland Cement

The storage of expended radioactive wastes is one of the most costly and important aspects of the use of nuclear energy, this is mainly due to the social and political concerns over environmental, safety and moral issues of storing the waste for hundreds and thousands of years.

Immobilisation of radioactive wastes is carried out to allow them to be handled and stored safely. Currently, OPC, BFS and PFA are used as an encapsulation matrix for intermediate level waste in the United Kingdom.  The high pH of the composite cement system limits the solubility of many present radioactive nuclides. However, these conditions can lead to corrosion of metals present in the waste; of particular significance is that of aluminium corrosion. The products of corrosion, hydrogen gas evolution and expansive hydroxides, can lead to poor wasteform quality, which raises questions about the environmental and safety case of cemented wasteforms.

In this work the complex OPC system is separated into easy to define pure systems in order to gain further understanding of the corrosion of aluminium simulant wastes within cement matrices. The pure phases, tricalcium silicate, dicalcium silicate, calcium aluminate and calcium aluminaferrite, are synthesised and then the corrosion of encapsulated aluminium is studied. The results enable a comparison between corrosion in OPC and pure phases to be drawn, which provides fundamental information on the governing mechanisms of the corrosion reactions, the products formed, and their effect on the systems.