The metamict state: Implications for radiation damage in crystalline waste forms

Abstract

The long term effect of radiation damage on waste disposal mediums, either crystalline or glass, is a factor in the evaluation of the “integrity” of the waste disposal mediums. Metamict minerals are a special class of amorphous materials which were initially crystalline. Although the mechanism for the loss of crystallinity in these minerals (mostly actinide containing oxides and silicates) is not clearly understood, damage caused by alpha particles and recoil nuclei is certainly critical to the metamictization process. Comparison of metamict and non-metamict polymorphs, such as thorite and huttonite (ThSiO 4), provides a basis for the evaluation of the susceptibility of different structure types to radiation damage. Short term radiation damage experiments of these phases can be validated by comparing the results to long term radiation damage observed in minerals, such as huttonite, thorite and zircon. This paper summarizes the pertinent literature on metamictization and proposes experiments to elucidate structural controls on radiation damage in crystalline phases.