Review of intermediate-scale field tests in support of disposal of waste forms.

Nuclear waste has been generated from commercial nuclear reactors and from past nuclear weapons production activities. The safe disposal of this waste generally is planned to involve emplacement of packaged spent nuclear fuel (SNF) into the subsurface or reprocessing the used nuclear fuel and producing a sparingly soluble mineral or glass. The high-level waste form(s) would then be packaged and sent to a geologic repository. High-level waste (HLW) is expected to be sent for deep geological disposal while the low-level waste (LLW) is to be stored in near-surface facilities. In order to design and manage a secure disposal site, the LLW and HLW waste forms must limit the release of radioactive materials to the surrounding environment for very long time periods. This stability is dependent on the waste form itself as well as the physical and chemical characteristics imposed by the surrounding engineered systems and geology. When studying the chemical durability of the waste form in a laboratory setting, it is not possible to capture all of the complex and coupled processes that the waste form would be subjected to in the disposal system. Intermediate-scale tests can improve understanding and close knowledge gaps that may arise when applying laboratory experiments to a larger scale. The present paper gives an overview of the literature available on the interactions of waste forms and the surrounding environment (engineered barriers and geological materials), as well as suggestions on overcoming existing uncertainties that may aid in more robust performance assessment models.