radAFM: Coupled radiation source/liquid-cell AFM to study radiation-induced interfacial processes
EMSL Project ID
50416
Abstract
Millions of liters of high-level radioactive wastes (HLW) stored in hundreds of tanks in the U.S. create a variety of environmental problems. To mitigate these problems, the wastes are intended to be processed for ultimate disposal as vitrified HLW, which is an extremely complicated and expensive task. At Hanford, construction of the Tank Waste Treatment and Immobilization Plant (WTP) is underway, but there are still critical knowledge gaps in waste tank chemistry, processing schemes, and waste rheology. This is because the tank waste is an extremely complex mixture of saltcake, metal (oxy)hydroxide sludge, and highly alkaline solutions of concentrated electrolytes that have been exposed to ionizing radiation for many decades. As they wait for processing, the wastes continue to age. Processes such as dissolution, nucleation, and growth occurring in these non-equilibrium environments involve extremes of pH, ionic strength and ionizing radiation. There is a need to understand and model these aging processes at a fundamental level to be able to predict their evolution over time.The proposed capability development project will enable a direct means to address a key aspect of this problem – the radiolytic aging of metal (oxy)hydroxides. Al and Fe (oxy)hydroxides are the main solid phase components of the HLW sludge. Radiation is known to stimulate dissolution of many metal (oxy)hydroxides in low-pH solutions, dramatically changing their physical and chemical properties, but there is practically no data for the highly alkaline conditions present in tank waste. Non-transparent liquid-solid interfaces are difficult to study in-situ under irradiation, but such information is absolutely necessary for basic understanding of the primary radiation-induced reactions. In the proposed research, we intend to overcome these obstacles by developing liquid cell Atomic Force Microscopy (AFM) in combination with controlled irradiation – x-rays and energetic electrons – for simulating the beta/gamma radiation environment in HLW storage. Challenges to the development of a radAFM are present but not insurmountable. Low-penetration radiation (x-rays and electrons) will deliver its energy to the solid/liquid interface, but both delivery and quantification of the fluence or doses associated with the ultra-small cross-sectional areas and volumes comprise one obstacle. Therefore producing and aiming microbeams, and measuring associated fluence and doses, is a very important part of the design. The proposed capability will be a powerful tool for studying radiation-induced processes microscopically with atomic-scale resolution. The radAFM will establish a unique capability for PNNL and set a new standard internationally for probing interfacial radiation-induced processes in situ under conditions closely mimicking stored HLW.
Project Details
Start Date
2018-07-02
End Date
2018-09-30
Status
Closed
Released Data Link
Team
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