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Title: Critical Role of Water Content in the Formation and Reactivity of Uraniu, Neptunium, and Plutonium Iodates Under Hydrothermal Conditions: Implications for the Oxidative Dissolution of Spent Nuclear Fuel

Abstract

The reactions of {sup 237}NpO{sub 2} with excess iodate under acidic hydrothermal conditions result in the isolation of the neptunium(IV), neptunium(V), and neptunium(VI) iodates, Np(IO{sub 3}){sub 4}, Np(IO{sub 3}){sub 4}{center_dot}nH{sub 2}O{center_dot}nHIO{sub 3}, NpO2(IO3), NpO2(IO3)2(H2O), and NpO{sub 2}(IO{sub 3}){sub 2}{center_dot}H{sub 2}O, depending on both the pH and the amount of water present in the reactions. Reactions with less water and lower pH favor reduced products. Although the initial redox processes involved in the reactions between {sup 237}NpO{sub 2} or {sup 242}PuO{sub 2} and iodate are similar, the low solubility of Pu(IO{sub 3}){sub 4} dominates product formation in plutonium iodate reactions to a much greater extent than does Np(IO{sub 3}){sub 4} in the neptunium iodate system. UO{sub 2} reacts with iodate under these conditions to yield uranium(VI) iodates solely. The isotypic structures of the actinide(IV) iodates, An(IO{sub 3}){sub 4} (An = Np, Pu), are reported and consist of one-dimensional chains of dodecahedral An(IV) cations bridged by iodate anions. The structure of Np(IO3)4{center_dot}nH2O{center_dot}nHIO3 is constructed from NpO9 tricapped-trigonal prisms that are bridged by iodate into a polar three-dimensional framework structure. Second-harmonic-generation measurements on a polycrystalline sample of the Th analogue of Np(IO{sub 3}){sub 4}{center_dot}nH{sub 2}O{center_dot}nHIO{sub 3} reveal a response of approximately 12x thatmore » of {alpha}-SiO{sub 2}. Single-crystal magnetic susceptibility measurements of Np(IO{sub 3}){sub 4} show magnetically isolated Np(IV) ions.« less

Authors:
 [1];  [1];  [2];  [2];  [3];  [4];  [5];  [1];  [1]
  1. Auburn University, Auburn, Alabama
  2. Florida State University
  3. Argonne National Laboratory (ANL)
  4. University of South Alabama, Mobile
  5. {Dick} G [ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
930871
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Inorganic Chemistry; Journal Volume: 46; Journal Issue: 9
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; ANIONS; CATIONS; CHAINS; DISSOLUTION; IODATES; MAGNETIC SUSCEPTIBILITY; NEPTUNIUM; NUCLEAR FUELS; PLUTONIUM; PRISMS; SOLUBILITY; URANIUM; WATER

Citation Formats

Bray, T. H., Ling, Jie, Choi, E- Sang, Brooks, James S., Beitz, James V., Sykora, Richard E., Haire, Richard, Stanbury, David M., and Albrecht-Schmitt, Thomas E. Critical Role of Water Content in the Formation and Reactivity of Uraniu, Neptunium, and Plutonium Iodates Under Hydrothermal Conditions: Implications for the Oxidative Dissolution of Spent Nuclear Fuel. United States: N. p., 2007. Web. doi:10.1021/ic070170d.
Bray, T. H., Ling, Jie, Choi, E- Sang, Brooks, James S., Beitz, James V., Sykora, Richard E., Haire, Richard, Stanbury, David M., & Albrecht-Schmitt, Thomas E. Critical Role of Water Content in the Formation and Reactivity of Uraniu, Neptunium, and Plutonium Iodates Under Hydrothermal Conditions: Implications for the Oxidative Dissolution of Spent Nuclear Fuel. United States. doi:10.1021/ic070170d.
Bray, T. H., Ling, Jie, Choi, E- Sang, Brooks, James S., Beitz, James V., Sykora, Richard E., Haire, Richard, Stanbury, David M., and Albrecht-Schmitt, Thomas E. Mon . "Critical Role of Water Content in the Formation and Reactivity of Uraniu, Neptunium, and Plutonium Iodates Under Hydrothermal Conditions: Implications for the Oxidative Dissolution of Spent Nuclear Fuel". United States. doi:10.1021/ic070170d.
@article{osti_930871,
title = {Critical Role of Water Content in the Formation and Reactivity of Uraniu, Neptunium, and Plutonium Iodates Under Hydrothermal Conditions: Implications for the Oxidative Dissolution of Spent Nuclear Fuel},
author = {Bray, T. H. and Ling, Jie and Choi, E- Sang and Brooks, James S. and Beitz, James V. and Sykora, Richard E. and Haire, Richard and Stanbury, David M. and Albrecht-Schmitt, Thomas E.},
abstractNote = {The reactions of {sup 237}NpO{sub 2} with excess iodate under acidic hydrothermal conditions result in the isolation of the neptunium(IV), neptunium(V), and neptunium(VI) iodates, Np(IO{sub 3}){sub 4}, Np(IO{sub 3}){sub 4}{center_dot}nH{sub 2}O{center_dot}nHIO{sub 3}, NpO2(IO3), NpO2(IO3)2(H2O), and NpO{sub 2}(IO{sub 3}){sub 2}{center_dot}H{sub 2}O, depending on both the pH and the amount of water present in the reactions. Reactions with less water and lower pH favor reduced products. Although the initial redox processes involved in the reactions between {sup 237}NpO{sub 2} or {sup 242}PuO{sub 2} and iodate are similar, the low solubility of Pu(IO{sub 3}){sub 4} dominates product formation in plutonium iodate reactions to a much greater extent than does Np(IO{sub 3}){sub 4} in the neptunium iodate system. UO{sub 2} reacts with iodate under these conditions to yield uranium(VI) iodates solely. The isotypic structures of the actinide(IV) iodates, An(IO{sub 3}){sub 4} (An = Np, Pu), are reported and consist of one-dimensional chains of dodecahedral An(IV) cations bridged by iodate anions. The structure of Np(IO3)4{center_dot}nH2O{center_dot}nHIO3 is constructed from NpO9 tricapped-trigonal prisms that are bridged by iodate into a polar three-dimensional framework structure. Second-harmonic-generation measurements on a polycrystalline sample of the Th analogue of Np(IO{sub 3}){sub 4}{center_dot}nH{sub 2}O{center_dot}nHIO{sub 3} reveal a response of approximately 12x that of {alpha}-SiO{sub 2}. Single-crystal magnetic susceptibility measurements of Np(IO{sub 3}){sub 4} show magnetically isolated Np(IV) ions.},
doi = {10.1021/ic070170d},
journal = {Inorganic Chemistry},
number = 9,
volume = 46,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Hydrothermally altered (225{degree}C) albite was compositionally depth-profiled using X-ray photoelectron spectroscopy (XPS) coupled with calibrated Ar ion sputtering. Solution data were collected during dissolution runs for the same crystals which were spectroscopically analyzed. We found that leached zones depleted in Na, Al, and O develop during the initial, incongruent phase of dissolution. Angle resolved XPS (ARXPS) demonstrated that Na and Al are significantly depleted from the upper few monolayers. Depths of leaching, which range from 10 to 900 {angstrom}, decrease with increasing pH in the acid region and increase with pH in the basic region. Based on calculated dissolution ratesmore » the depth of leaching can be roughly correlated with the release rate of Si. Preliminary evaluations of diffusion transport rates through leached layers suggest that dissolution is not rate limited by diffusion. Instead, the kinetics of dissolution seem to be related to the intrinsic rate of structural hydrolysis. Using the XPS and solution data in conjunction with theoretical and experimental studies in the literature, we propose a dissolution mechanism based on initial ion exchange followed by the hydrolysis of Al and Si, which is modeled as the breakdown of activated complexes formed at bridging oxygen (O{sub br}) sites. Elemental mass balances based on comparisons between the XPS and solution data suggest that dissolution occurs non-uniformly and is probably preferentially constrained to dislocations and macroscopic defects within the structure.« less
  • When released out of a canister, the radionuclides originally incorporated in the spent fuel can still deposit radiation energy (even more efficiently) into the pore water, cause water radiolysis, and produce oxidants in the buffering material. This phenomenon is termed secondary water radiolysis. The oxidants thus produced can possibly diffuse back to oxidize the spent fuel and to increase the oxidative dissolution rate of the fuel.The effect of the secondary water radiolysis has been identified and preliminarily addressed by a mass-balance model. To explore whether the effect is significant on spent-fuel dissolution, the upper-boundary limit of the effect has beenmore » set up by considering a scenario that is very unlikely to occur. Several extreme assumptions have been made: First, the canister fails completely 10{sup 3} yr after deposition; second, the spent fuel is oxidized instantaneously; and third, the radionuclides considered are those that dominantly contribute to radiolysis between 10{sup 3} to 10{sup 5} yr. With these assumptions, the spent-fuel dissolution rate can be increased dramatically if 10% or more of the oxidants produced by the secondary water radiolysis diffuse back to oxidize the spent fuel. It thus indicates that the effect of the secondary water radiolysis could be significant with some extreme assumptions. With more realistic assumptions, the effect could possibly become minimal. The subject is worth further investigation.« less
  • The specific feature of multi-component oxides synthesized by hydrothermal process under high temperature (633 K) and highly pressurized water (18.9 MPa) near critical point. Effects of hydrothermal processing duration times 24 hours and 72 hours, respectively, on the oxide formation of the Ni{sub 59}Zr{sub 20}Ti{sub 16}Si{sub 2}Sn{sub 3} metallic glass synthesized by powder metallurgy process were characterized by X-ray diffractometer, differential scanning calorimeter along with the particle size, morphology and crystalline phase of the oxides. The crystallization of the needle-shape NiTiO{sub 3}, ZrTiO{sub 4} and ZrSnO{sub 4} ternary oxide phases observed on the surface of metallic glass at below glassmore » transition temperature and the morphology of oxide phases changed to plate-shape around 2 μm in diameter by the increase processing time. This hydrothermal processing in subcritical water provides accelerated dense metal oxide crystals due to the reaction medium being at higher pressure than conventional oxidation processing.« less
  • The specific feature of multi-component oxides synthesized by hydrothermal process under high temperature (633 K) and highly pressurized water (18.9 MPa) near critical point. Effects of hydrothermal processing duration times 24 hours and 72 hours, respectively, on the oxide formation of the Ni 59Zr 20Ti 16Si 2Sn 3 metallic glass synthesized by powder metallurgy process were characterized by X-ray diffractometer, differential scanning calorimeter along with the particle size, morphology and crystalline phase of the oxides. The crystallization of the needle-shape NiTiO 3, ZrTiO 4 and ZrSnO 4 ternary oxide phases observed on the surface of metallic glass at below glassmore » transition temperature and the morphology of oxide phases changed to plate-shape around 2 μm in diameter by the increase processing time. This hydrothermal processing in subcritical water provides accelerated dense metal oxide crystals due to the reaction medium being at higher pressure than conventional oxidation processing.« less
  • In the original manuscript, M. H. Lee’s affiliation number was incorrectly listed as 1. M. H. Lee’s correct affiliation number is 2 (Rare Metals R&D Group, Korea Institute of Industrial Technology, Incheon 406-840, South Korea). Furthermore, this change affects no other part of the paper.