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Title: Impeding 99Tc(IV) mobility in novel waste forms

Abstract

Technetium ( 99Tc) is a long-lived radioactive fission product whose mobility in the subsurface is largely governed by its oxidation state1. Immobilization of Tc in mineral substrates is crucial for radioactive waste management and environmental remediation. Tc(IV) incorporation in spinels2, 3 has been proposed as a novel method to increase Tc retention in glass waste forms. However, experiments with Tc-magnetite under high temperature and oxic conditions showed re-oxidation of Tc(IV) to volatile pertechnetate Tc(VII)O4-.4, 5 Here we address this problem with large-scale ab initio molecular dynamics simulations and propose that elevated temperatures, 1st row transition metal dopants can significantly enhance Tc retention in the order Co > Zn > Ni. Experiments with doped spinels at T=700 ºC provided quantitative confirmation of increased Tc retention in the same order predicted by theory. This work highlights the power of modern state-of-the-art simulations to provide essential insights and generate bottom-up design criteria of complex oxide materials at elevated temperatures.

Authors:
 [1];  [2];  [3];  [4];  [5];  [1];  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Fundamental and Computational Sciences Directorate
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Energy and Environment Directorate; Pohang Univ. of Science and Technology (POSTECH) (South Korea)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Energy and Environment Directorate
  4. United States Dept. of Energy, Richland, WA (United States). Office of River Protection
  5. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1282477
Alternate Identifier(s):
OSTI ID: 1436595
Report Number(s):
PNNL-SA-114552
Journal ID: ISSN 2041-1723; 830403000
Grant/Contract Number:
AC05-76RL01830; AC02-05CH11231; AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 7; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES

Citation Formats

Lee, Mal-Soon, Um, Wooyong, Wang, Guohui, Kruger, Albert A., Lukens, Wayne W., Rousseau, Roger, and Glezakou, Vassiliki-Alexandra. Impeding 99Tc(IV) mobility in novel waste forms. United States: N. p., 2016. Web. doi:10.1038/ncomms12067.
Lee, Mal-Soon, Um, Wooyong, Wang, Guohui, Kruger, Albert A., Lukens, Wayne W., Rousseau, Roger, & Glezakou, Vassiliki-Alexandra. Impeding 99Tc(IV) mobility in novel waste forms. United States. doi:10.1038/ncomms12067.
Lee, Mal-Soon, Um, Wooyong, Wang, Guohui, Kruger, Albert A., Lukens, Wayne W., Rousseau, Roger, and Glezakou, Vassiliki-Alexandra. Thu . "Impeding 99Tc(IV) mobility in novel waste forms". United States. doi:10.1038/ncomms12067. https://www.osti.gov/servlets/purl/1282477.
@article{osti_1282477,
title = {Impeding 99Tc(IV) mobility in novel waste forms},
author = {Lee, Mal-Soon and Um, Wooyong and Wang, Guohui and Kruger, Albert A. and Lukens, Wayne W. and Rousseau, Roger and Glezakou, Vassiliki-Alexandra},
abstractNote = {Technetium (99Tc) is a long-lived radioactive fission product whose mobility in the subsurface is largely governed by its oxidation state1. Immobilization of Tc in mineral substrates is crucial for radioactive waste management and environmental remediation. Tc(IV) incorporation in spinels2, 3 has been proposed as a novel method to increase Tc retention in glass waste forms. However, experiments with Tc-magnetite under high temperature and oxic conditions showed re-oxidation of Tc(IV) to volatile pertechnetate Tc(VII)O4-.4, 5 Here we address this problem with large-scale ab initio molecular dynamics simulations and propose that elevated temperatures, 1st row transition metal dopants can significantly enhance Tc retention in the order Co > Zn > Ni. Experiments with doped spinels at T=700 ºC provided quantitative confirmation of increased Tc retention in the same order predicted by theory. This work highlights the power of modern state-of-the-art simulations to provide essential insights and generate bottom-up design criteria of complex oxide materials at elevated temperatures.},
doi = {10.1038/ncomms12067},
journal = {Nature Communications},
number = ,
volume = 7,
place = {United States},
year = {Thu Jun 30 00:00:00 EDT 2016},
month = {Thu Jun 30 00:00:00 EDT 2016}
}

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Cited by: 9works
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  • Technetium ( 99 Tc) is an abundant, long-lived radioactive fission product whose mobility in the subsurface is largely governed by its oxidation state. Tc immobilization is crucial for radioactive waste management and environmental remediation. Tc(IV) incorporation in spinels has been proposed as a novel method to increase Tc retention in glass waste forms during vitrification. However, experiments under high-temperature and oxic conditions show reoxidation of Tc(IV) to volatile pertechnetate, Tc(VII). Here we examine this problem with ab initio molecular dynamics simulations and propose that, at elevated temperatures, doping with first row transition metal can significantly enhance Tc retention in magnetitemore » in the order Co > Zn > Ni. Experiments with doped spinels at 700 °C provide quantitative confirmation of the theoretical predictions in the same order. This work highlights the power of modern, state-of-the-art simulations to provide essential insights and generate theory-inspired design criteria of complex materials at elevated temperatures.« less
  • The preparation, elemental and titrimetric analysis, magnetic properties, and optical spectrum of (H/sub 2/EDTA)/sup 99/Tc/sup IV/(..mu..-O)/sub 2//sup 99/Tc/sup IV/(H/sub 2/EDTA).5H/sub 2/O are described. An x-ray structure determination (R/sub w/ = 0.047) shows an almost planar four-membered Tc(..mu..-O)/sub 2/Tc ring. Each EDTA coordinates to one Tc by two N's and two O's, and two carboxylate groups are protonated and noncoordinating (Figure 1). Interatomic distances provide strong support for a Tc(IV) oxidation state. The Tc-Tc distance is short at 2.33 A; the molecule is diamagnetic and shows a strong optical absorption band at 20,200 cm/sup -1/ (epsilon approx. 2000). Extended Hueckel calculationsmore » suggest a partly antibonding sigma/sup 2/..pi../sup 2/delta*/sup 2/ configuration for the six metal d electrons rather than the fully bonding sigma/sup 2/..pi../sup 2/delta/sup 2/ configuration expected from naive application of the 18-electron rule. None of the available evidence contradicts this assignment, but more experiments are needed to prove it.« less
  • We present that technetium ( 99Tc) immobilization by doping into iron oxide mineral phases may alleviate the problems with Tc volatility during vitrification of nuclear waste. Because reduced Tc, Tc(IV), substitutes for Fe(III) in the crystal structure by a process of Tc reduction from Tc(VII) to Tc(IV) followed by co-precipitation of Fe oxide minerals, two Tc-incorporated Fe minerals (Tc-goethite and Tc-magnetite/maghemite) were prepared and tested for Tc retention in glass melt samples at temperatures between 600 and 1000 °C. After being cooled, the solid glass specimens prepared at different temperatures at 600, 800, and 1000 °C were analyzed for Tcmore » oxidation state using Tc K-edge XANES. In most samples, Tc was partially (<60%) oxidized from Tc(IV) to Tc(VII) as the melt temperature increased up to 600 °C. However, most of Tc(IV) was completely (>95%) oxidized to Tc(VII) at temperature above 800 °C. Tc retention in glass melt samples prepared using Tc-incorporated Fe minerals were slightly higher (~10%) than in glass prepared using KTcO4 because of limited and delayed Tc volatilization.« less
  • The activation cross sections for the [sup 99]Tc(n,p)[sup 99]Mo, [sup 99]Tc(n,[alpha])[sup 96]Nb, [sup 99]Tc(n,n[prime][alpha])[sup 95]Nb, and [sup 99]Tc(n,n[prime])[sup 99n]Tc reactions at 13.5 and 14.8 MeV have been measured by using the deuterium-tritium neutron generator (the Fusion Neutronics Source) at the Japan Atomic Energy Research Institute. The results were compared with experimental values form the literature, evaluated activation cross-section files, and predictions by current cross-section computer codes. Special emphasis was placed on the feasibility of producing high-specific-activity [sup 99]Mo, to be used in medical applications, via the [sup 99]Tc(n,p)[sup 99]Mo reaction in the Fusion Material Irradiation Facility. A factor of 3more » overestimate of [sup 99]Mo production resulted when the REAC[sup *]2 code was used. It is suggested that this discrepancy is due primarily to the factor of 5 difference in cross sections at the 14-MeV region between the REAC*2 data and the current measurement.« less