Pyrochlore-structured titanate ceramics for immobilisation of actinides: Hot isostatic pressing (HIPing) and stainless steel/waste form interactions

A pyrochlore-structured titanate ceramic has been studied in respect of its overall feasibility for immobilisation of impure actinide-rich radioactive wastes through the hot isostatic pressing (HIPing) technique. The resultant waste form contains mainly pyrochlore (∼70%), rutile (∼14%) as well as perovskite (∼12%), hollandite (∼2%) and brannerite (∼1%). Optical spectroscopy confirms that uranium (used to simulate Pu) exists mainly in the stable pyrochlore-structured phase as tetravalent ions as designed. The stainless steel/waste form interactions under HIPing conditions (1280 °C/100 MPa/3 h) do not seem to change the actinide-bearing phases and therefore should have no detrimental effect on the waste form.