Evolution of technetium speciation in reducing grout Metadata

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Title

  • Main Title Evolution of technetium speciation in reducing grout

Creator

  • Author: Lukens, Wayne W.
    Creator Type: Personal
  • Author: Bucher, Jerome J.
    Creator Type: Personal
  • Author: Shuh, David K.
    Creator Type: Personal
  • Author: Edelstein,Norman M.
    Creator Type: Personal

Contributor

  • Sponsor: USDOE Director. Office of Science. Office of Basic EnergySciences, Office of Science and Technology, Environmental ManagementScience Program
    Contributor Type: Organization

Publisher

  • Name: Lawrence Berkeley National Laboratory
    Place of Publication: Berkeley, California
    Additional Info: "Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (United States)"

Date

  • Creation: 2003-11-24

Language

  • English

Description

  • Content Description: Cementitious waste forms (CWFs) are an important component of the strategy to immobilize high-level nuclear waste resulting from plutonium production by the U.S. Department of Energy (DOE). Technetium (99Tc) is an abundant fission product of particular concern in CWFs due to the high solubility and mobility of pertechnetate, TcO4-, the stable form of technetium in aerobic environments. CWFs can more effectively immobilize 99Tc if they contain additives that reduce mobile TcO4- to immobile Tc(IV) species. Leaching of 99Tc from reducing CWFs that contain Tc(IV) is much slower than for CWFs containing TcO4-. Previous X-ray absorption fine structure (XAFS) studies showed that the Tc(IV) species were oxidized to TcO4- in reducing grout samples prepared on a laboratory scale. Whether the oxidizer was atmospheric O2 or NO3- in the waste simulant was not determined. In actual CWFs, rapid oxidation of Tc(IV) by NO3- would be a concern, whereas oxidation by atmospheric O2 would be of less concern due to the slow diffusion and reaction of O2 with the reducing CWF. To address this uncertainty, two series of reducing grouts were prepared using TcO4- containing waste simulants with and without NO3-. In the first series of samples, the TcO4- was completely reduced using Na2S, and the samples were placed in containers that permitted O2 diffusion. In these samples, all of the technetium was initially present as aTc(IV) sulfide compound, TcSx, which was characterized using extended X-ray absorption fine structure (EXAFS) spectroscopy, and is likely Tc2S7. The TcSx initially present in the grout samples was steadily oxidized over 4 years. In the second series of samples, all of the TcO4- was not initially reduced, and the grout samples were placed in airtight containers. In these samples, the remaining TcO4- continued to be reduced as the samples aged, presumably due to the presence of reducing blast furnace slag. When samples in the second series were exposed to atmosphere, the lower-valent technetium species were rapidly oxidized to TcO4-.

Subject

  • Keyword: Oxidizers
  • Keyword: Oxidation
  • Keyword: Sulfides
  • Keyword: Solubility
  • STI Subject Categories: 12 Management Of Radioactive Wastes, And Non-Radioactive Wastes From Nuclear Facilities
  • Keyword: Grouting
  • Keyword: Wastes Technetium Grout Cement Nuclear Waste
  • Keyword: Diffusion
  • Keyword: Technetium Grout Cement Nuclear Waste
  • Keyword: Fission Products
  • Keyword: Spectroscopy
  • Keyword: Plutonium
  • Keyword: Leaching
  • Keyword: Radioactive Wastes
  • Keyword: Waste Forms
  • STI Subject Categories: 11 Nuclear Fuel Cycle And Fuel Materials
  • Keyword: Fine Structure
  • Keyword: Absorption
  • Keyword: Additives
  • Keyword: Technetium
  • Keyword: Blast Furnaces
  • Keyword: Containers

Source

  • Journal Name: Environmental Science and Technology; Journal Volume: 39; Journal Issue: 20; Related Information: Journal Publication Date: 10/15/2005

Collection

  • Name: Office of Scientific & Technical Information Technical Reports
    Code: OSTI

Institution

  • Name: UNT Libraries Government Documents Department
    Code: UNTGD

Resource Type

  • Article

Format

  • Text

Identifier

  • Report No.: LBNL--54094
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 886605
  • Archival Resource Key: ark:/67531/metadc874366
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