Technetium and iodine getters to improve Cast Stone performance - 15420

Conference · Wed Jul 01 00:00:00 EDT 2015

OSTI ID:22824327

Asmussen, R. Matthew; Neeway, James J.; Lawter, Amanda R. ^[1]; Lukens, Wayne ^[2]; Qafoku, Nikolla P. ^[1]

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1. Pacific Northwest National Laboratory (United States)
2. Lawrence Berkeley National Laboratory (United States)

Technetium-99 ({sup 99}Tc) and iodine-129 ({sup 129}I) have been determined to be tank waste components contributing most to the environmental impacts associated with the cleanup of the Hanford site. Cast Stone, which has the ability to immobilize {sup 99}Tc, {sup 129}I, and other contaminants of concern, is being considered as a low temperature waste form for solidification of aqueous secondary liquid effluents from the Hanford Tank Waste Treatment and Immobilization Plant (WTP) An environmental assessment of Cast Stone performance, using measured diffusivities of the radionuclides from the Cast Stone product, calculates groundwater at the 100 m down-gradient in excess of the allowable maximum permissible concentrations for both radionuclides. Therefore, an opportunity exists to improve the performance of Cast Stone. One method for improvement is through the addition of immobilizing agents known as 'getters' that selectively sequester Tc and I. In the present paper, we report on seven getter materials that have been tested for Tc and five materials that have been tested for I to determine their effectiveness for radionuclide removal in a series of batch sorption tests in 18.2 MΩ DI H{sub 2}O and a 7.8 M Na Ave LAW waste simulant. Contact experiments have been carried out in anoxic conditions at room temperature, with varying solid-to-solution ratios, and in the presence and absence of competing species. Results indicate that most materials perform better in the 18.2 MΩ DI H{sub 2}O compared to the 7.8 M Na LAW waste simulant for both Tc and I getter. Radionuclide sequestration may be affected by the presence of the redox sensitive Cr(VI) in the simulant. The top performing Tc getter materials, Sn(II)-apatite, BFS-2, KMS-2 and Sn-hydroxyapatite, were examined through various solid-state characterization techniques such as SEM/XEDS, XANES and EXAFS. Tc removal is theorized to occur through reduction of the highly soluble Tc(VII) species to the less soluble Tc(IV). Solution results from the series of I tests show that iodide is effectively removed from solution via, most likely, a precipitation reaction of AgI. A wide range of I getter materials and the silver exchanged zeolite getter performed well in both DI water and the simulant. (authors)

• Research Organization: WM Symposia, Inc., PO Box 27646, 85285-7646 Tempe, AZ (United States)
• OSTI ID: 22824327
• Report Number(s): INIS-US-19-WM-15420; TRN: US19V0899069373
• Resource Relation: Conference: WM2015: Annual Waste Management Symposium, Phoenix, AZ (United States), 15-19 Mar 2015; Other Information: Country of input: France; 15 refs.; available online at: http://archive.wmsym.org/2015/index.html
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
ABSORPTION SPECTROSCOPY
APATITES
DECONTAMINATION
ENVIRONMENTAL IMPACTS
GETTERS
GROUND WATER
HANFORD RESERVATION
IODINE 129
LIQUID WASTES
MAXIMUM PERMISSIBLE CONCENTRATION
PRECIPITATION
SCANNING ELECTRON MICROSCOPY
SILVER IODIDES
SOLIDIFICATION
SOLIDS
SOLUTIONS
SORPTION
TANKS
TECHNETIUM 99
WASTE FORMS
WASTE PROCESSING
X-RAY SPECTROSCOPY
ZEOLITES