We intend to use neutron diffraction and x-ray diffraction to investigate the structure of potassium and barium iron phosphate glasses, which are potential candidate systems for radioactive waste immobilisation, as functions of the level and type of modifier addition. Structural changes in the glasses will be identified and will provide an understanding of the structural origins of the divergence in key physical properties, chiefly chemical durability, of the two systems. By obtaining a more detailed understanding of the relationship between structure and properties in these novel glass systems, it will be possible to optimise them for the safe immobilisation of some of our most dangerous radioactive wastes. Moreover, the excellent physical properties of these glasses may lead to new functionalities and novel applications in other fields.