Colloid-Facilitated Actinide Transport in a Cementitious-Impacted SRS Groundwater

Technical Report · Fri Apr 01 04:00:00 EDT 2022

DOI:https://doi.org/10.2172/1866068· OSTI ID:1866068

Kaplan, Daniel I. ^[1]

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1. Savannah River Nuclear Solutions (SRNS), Aiken, SC (United States); Savannah River National Laboratory (SRNL), Aiken, SC (United States)

The objective of this report is to provide a literature review relevant to the question of whether colloid facilitated transport of plutonium is enhanced in a cementitious groundwater system on the Savannah River Site (SRS). Contaminant transport is commonly described as taking place in a system with a mobile aqueous phase and an immobile solid phase. There has been an increasing awareness of a third phase, a mobile solid phase, also referred to as a mobile colloidal phase. Mobile colloids consist of organic and/or inorganic submicron-particles that move with groundwater flow. When radionuclides are associated with the mobile colloids, the net effect is that radionuclides can move faster through the subsurface system than would be predicted by transport models that do not include mobile colloids. It is important to distinguish between subsurface colloids and subsurface mobile colloids. The subsurface environment includes an enormous reservoir of colloids, but only a tiny fraction, if any, are mobile. Mobile colloid formation is commonly described as involving a three-step process: genesis, stabilization, and transport. It was concluded that there is a strong likelihood that submicron colloids of plutonium exist near the source term, (i.e., the genesis step is likely completed). While such particles have not been directly detected, it is highly likely that plutonium could either attach to submicron particles in the sediment or that submicron plutonium fragments exist at the source. However, the tendency for these plutonium colloids to move in the SRS subsurface is extremely low, especially in engineered cementitious environments where the ionic strength of the solution and the elevated concentrations of divalent cations greatly curtails colloid suspension stability (i.e., the stabilization step is likely not completed). Together these data strongly indicate that plutonium-bearing colloids would likely exist in the near field of a tank closure facility, but the colloids would be unlikely to be mobile, thereby providing a vector for enhanced transport. Under cementitious leachate impacted groundwater conditions, it is reasonable to assume plutonium transport occurs primarily as a two-phase system, a mobile aqueous phase and an immobile solid phase.

• Research Organization: Savannah River Site (SRS), Aiken, SC (United States); Savannah River National Lab (SRNL), Aiken, SC (United States)
• Sponsoring Organization: USDOE Office of Environmental Management (EM)
• DOE Contract Number: 89303321CEM000080
• OSTI ID: 1866068
• Report Number(s): SRNL-STI-2022-00169
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
cement
groundwater
mobile colloids
performance assessment
plutonium