Cementitious Wasteforms for Immobilization of Low-Activity Radioactive Wastes

Conference · Sun May 24 00:00:00 EDT 2009

DOI:https://doi.org/10.1557/PROC-1193-349· OSTI ID:1039134

Wellman, Dawn M; Bovaird, Chase C; Parker, Kent E; Cordova, Elsa A; Davis, Aaron M; Mattigod, Shas V; Powers, Laura; Wood, Marcus I

Solidification of low-activity wastes with cementitious materials is a widely accepted technique that contains and isolates waste from the hydrologic environment. The radionuclides I-129, Se-75, Tc-99, and U-238 are identified as long-term dose contributors. The anionic nature of these radionuclides in aqueous solutions allows them to readily leach into the subsurface environment. Any failure of concrete encasement may result in water intrusion and consequent mobilization of radionuclides from the waste packages via mass flow and/or diffusion into the surrounding subsurface environment. Assessing the long-term performance of waste grouts for encasement of radionuclides requires understanding the: (1) speciation and interaction of the radionuclides within the concrete wasteform, (2) diffusion of radionuclide species when contacted with vadose zone porewater or groundwater under environmentally relevant conditions, and (3) long-term durability and weathering of concrete waste forms. An improved understanding of the interactions of long-lived radionuclides in cementitious matrices will improve predictions of the long-term fate of these sequestered contaminants. An integrated laboratory investigation has been conducted including: (1) a multifaceted spectroscopic investigation to interrogate the speciation and interaction of radionuclides within concrete wasteforms, (2) solubility tests to quantify the stability of solid phases identified as radionuclide-controlling phases, (3) quantify the diffusion of radionuclides from concrete wasteforms into surrounding subsurface sediment under realistic moisture contents (4%, 7%, and 15% by weight moisture content), (4) quantify the long-term durability of concrete waste forms as a function environmental parameters relevant to depository conditions, and (5) identify the formation of secondary phases or processes (microcracking) that influence radionuclide retention. Data obtained from this investigation provides valuable information for understanding the speciation, behavior, and fate of radionuclides immobilized within concrete wasteforms under vadose zone conditions and underscores the necessity for robust, multi-disciplinary performance assessments for concrete waste forms.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1039134
• Report Number(s): PNNL-SA-66511; 830403000; TRN: US1202076
• Resource Relation: Conference: MRS Symposium Proceedings Series: 2009 MRS Spring Meeting - Scientific Basis for Nuclear Waste Management XXXIII, May 24-29, 2009, St Petersburg, Russia, 1193:Paper No. 349
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
AQUEOUS SOLUTIONS
CONCRETES
DIFFUSION
GROUTING
MANAGEMENT
MATRICES
MOISTURE
PERFORMANCE
RADIOACTIVE WASTES
RADIOISOTOPES
RETENTION
SEDIMENTS
SOLIDIFICATION
SOLUBILITY
STABILITY
WASTE FORMS
WASTES
WATER INFLUX
WEATHERING