Review of the Scientific Understanding of Radioactive Waste at the U.S. DOE Hanford Site

Abstract

This Critical Review reviews the origin and chemical and rheological complexity of radioactive waste at the U.S. Department of Energy Hanford Site. The waste, stored in underground tanks, was generated via three distinct processes over decades of plutonium extraction operations. Although close records were kept of original waste disposition, tank-to-tank transfers and conditions that impede equilibrium complicate our understanding of the chemistry, phase composition, and rheology of the waste. Tank waste slurries comprise particles and aggregates from nano to micro scales, with varying densities, morphologies, heterogeneous compositions, and complicated responses to flow regimes and process conditions. Further, remnant or changing radiation fields may affect the stability and rheology of the waste. These conditions pose challenges for transport through conduits or pipes to treatment plants for vitrification. Additionally, recalcitrant boehmite degrades glass quality and the high aluminum content must be reduced prior to vitrification for the manufacture of waste glass of acceptable durability. However, caustic leaching indicates that boehmite dissolves much more slowly than predicted given surface normalized rates. Existing empirical models based on ex situ experiments and observations generally only describe material balances and have not effectively predicted process performance. Recent advances in the areas of in situ microscopy, aberration-corrected transmission electron microscopy, theoretical modeling across scales, and experimental methods for probing the physics and chemistry at mineral-fluid and mineral-mineral interfaces are being implemented to build robustly predictive physics-based models.

Inference of principal species in caustic aluminate solutions through solid-state spectroscopic characterization

“…For example, understanding how the dominant tetrahedrallycoordinated aluminate anion, Al(OH) 4 -, transforms to octahedral aluminum (Al) during the precipitation of gibbsite, α-Al(OH) 3 , is key to the efficiency of the Bayer process by which alumina, Al 2 O 3 , is extracted from bauxite ore. [1][2][3] Despite the fact that the Bayer process was invented over 120 years ago and is still used to produce nearly all of the world's Al 2 O 3 supply as an intermediate step to Al production, the mechanism and kinetics of α-Al(OH) 3 precipitation have not been comprehensively described. [4][5][6][7][8][9] Both synthetic and industrial Bayer liquors have a propensity to become supersaturated, 10,11 presenting a considerable engineering challenge as α-Al(OH) 3 precipitation suffers from slow kinetics and yields are poor even in the presence of seed crystals. 12,13 Limited mechanistic understanding of how small Al clusters of low nuclearity condense into extended sheet structures of Al octahedra in α-Al(OH) 3 , or boehmite, AlO(OH) also directly hampers the processing of ca.…”

“…90 million gallons of highly caustic radioactive waste at U.S. Department of Energy legacy sites. 4,[14][15][16] These wastes contain significant quantities of solid and solvated Al forms that originated from disposed Al-clad defense fuels and are highly caustic due to NaOH additions used to increase the lifetime of underground steel storage tanks. 17 For such systems, developing the ability to spectroscopically distinguish the principal aluminum species in solution in equilibrium with α-Al(OH) 3 is critical.…”

Synthesis and Sorption Properties towards Sr-90 of Composite Sorbents Based on Magnetite and Hematite

“…Currently, scientists working in the field of radiochemistry are facing a challenge of creating efficient materials for treatment of the clarified part of heterogeneous liquid radioactive waste (LRW) streams accumulated in the process of the nuclear weapon production in order to remove Sr-90. The chemical composition of the clarified part of heterogeneous LRW is mainly represented by Na + ions (more than 1 mol/L) in the forms of nitrites and nitrates, as well as OH − (more than 0.5 mol/L) [1][2][3].…”

Effects of Al:Si and (Al + Na):Si ratios on the properties of the international simple glass, part I: Physical properties

“…Hanford site has unique challenges because, as the first large‐scale reprocessing site in the world, many evolving chemical separation processes were tested and adapted. Early processes generated significantly more nuclear waste than the modern embodiment of PUREX reprocessing method, 1 in large part due to the addition of large quantities of nonradioactive chemicals to the waste stream such as aluminum (added primarily in the REDOX solvent extraction process and from fuel cladding during its removal process). Roughly half of the high‐level tank waste (HLW) at Hanford falls within the “high‐alumina” group which contains between 42 and nearly 100 wt% Al 2 O 3 2 …”