Ceramic Nuclear Waste Forms Research Articles

Magnesium Titanate Spinel: A Ceramic Phase for Immobilization of Technetium‐99 from Radioactive Wastes

Technetium‐99 can be dissolved in Mg2TiO4 spinels to form solid solutions with low dissolution rates. These materials are possible host phases for 99Tc in ceramic nuclear waste forms.

NZP], a new radiophase for ceramic nuclear waste forms

The NZP structure is a candidate for immobilization of certain types of nuclear waste. It will incorporate 137Cs, 90Sr, and a range of other nuclides. The leach resistance of CsZr 2(PO 4) 3 appears to be comparable with that of other phases under consideration for radio-Cs immobilization. This phase can be formed by sintering at ∼850°C; it is reasonably refractory, and it is compatible with monazite, a favored immobilizing agent for waste actinides.

Dissolution of tailored ceramic nuclear waste forms

Dissolution experiments on polyphase, high alumina tailored ceramic nuclear waste forms developed for the chemical immobilization of Savannah River Plant nuclear waste are described. Three forms of leach tests have been adopted; bulk samples conforming to the Materials Characterization Center Static Leach Test (MCC-1), a powdered sample leach test, and a leach test performed on transmission electron microscope thin foil samples. From analysis of these tests the crystalline phases that preferentially dissolve on leaching and the product phases formed are identified and related to the tailoring and processing schemes used in forming the ceramics. The thin foil sample leaching enables the role of intergranular amorphous phases as short-circuit leaching paths in polyphase ceramics to be investigated.

ChemInform Abstract: PHASE RELATIONS IN CRYSTALLINE CERAMIC NUCLEAR WASTE FORMS: THE SYSTEM UO2+X‐CEO2‐ZRO2‐THO2 AT 1200°C IN AIR

Steady-state phase relations in the system UO2+x-CeOz-ZrO2-ThO2 were determined for application to phase relations in high-level crystalline ceramic nuclear waste forms. Samples were treated at 1200°C at an oxygen partial pressure of 21.3 kPa and a total pressure of 101.3 kPa. Phase assemblages were found to be comprised of cubic solid solutions of the fluorite-structure type, solid solutions based on ZrO2, and orthorhombic solid solutions based on U3O8.

Phase Relations in Crystalline Ceramic Nuclear Waste Forms: The System UO2+x‐CeO2‐ZrO2‐ThO2 at 1200°C in Air

Steady‐state phase relations in the system UO2+x‐CeOz‐ZrO2‐ThO2 were determined for application to phase relations in high‐level crystalline ceramic nuclear waste forms. Samples were treated at 1200°C at an oxygen partial pressure of 21.3 kPa and a total pressure of 101.3 kPa. Phase assemblages were found to be comprised of cubic solid solutions of the fluorite‐structure type, solid solutions based on ZrO2, and orthorhombic solid solutions based on U3O8.

A Study of Radiation Effects in Curium-Doped Gd2Ti2O7 (Pyrochlore) and CaZrTi2O7 (Zirconolite)

Radiation effects studies in both glass and glass ceramic nuclear waste forms have identified a rare-earth titanate phase of the general formula (RE) 2Ti207 which is capable of acting as a host phase for actinides.1,2 Ringwood and co-workers3 have also proposed a structurally similar phase, zirconolite (CaZrTi2 07), as one of the primary host phases in the SYNROC waste form. Data from these and other previous studies, as well as mineralogical information available on these titanate phases, have not provided an unambiguous interpretation of the effects of radiation damage relative to nuclear waste forms. This paper reports new laboratory data concerning radiation damage effects in both of these phases.