An estimate of the inventory of technetium-99 in the sub-tidal sediments of the Irish Sea

Jenkinson, S B; McCubbin, D.; Kennedy, P.; Dewar, Alastair; Bonfield, Rachel; Leonard, K.S.

doi:10.1016/j.jenvrad.2013.05.004

Cited by 14 publications

(7 citation statements)

References 15 publications

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“…Significantly higher concentrations up to 2.2 × 10 11 atoms/g (36 pg/g) were found in forest soil within the 30 km-zone from the Chernobyl NPP . In the reference material IAEA-443, an Irish Sea water sample affected by the liquid discharges of the Sellafield reprocessing plant, an information value for the concentration of 99 Tc of (1.9 ± 0.4) × 10 9 atoms/mL (312 fg/g) is given. , Subtidal sediments of the Sellafield offshore area present significantly higher levels of 99 Tc, and, in fact, up to ∼4.8 × 10 atoms/g (79 pg/g) of 99 Tc were determined in a sediment core collected in 2005 …”

Section: Analytical Techniquesmentioning

confidence: 94%

“…8,9 Subtidal sediments of the Sellafield offshore area present significantly higher levels of 99 Tc, and, in fact, up to ∼4.8 × 10 11 atoms/g (79 pg/g) of 99 Tc were determined in a sediment core collected in 2005. 10 Because of its long half-life and high fission yield, 99 Tc would be one of the major contributors until ∼6 × 10 5 year to the long-term radiotoxicity of spent nuclear fuel. 11 To ensure a safe geological disposal of nuclear waste, the environmental behavior of Tc, occurring under oxidizing conditions as the highly mobile pertechnetate, 5 must be understood.…”

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confidence: 99%

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Ultratrace Determination of ⁹⁹Tc in Small Natural Water Samples by Accelerator Mass Spectrometry with the Gas-Filled Analyzing Magnet System

et al. 2019

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In the frame of studies on the safe disposal of nuclear waste, there is a great interest for understanding the migration behavior of 99Tc. 99Tc originating from nuclear energy production and global fallout shows environmental levels down to 107 atoms/g of soil (∼2 fg/g). Extremely low concentrations are also expected in groundwater after diffusion of 99Tc through the bentonite constituting the technical barrier for nuclear waste disposal. The main limitation to the sensitivity of the mass spectrometric analysis of 99Tc is the background of its stable isobar 99Ru. For ultratrace analysis, the Accelerator Mass Spectrometry (AMS) setup of the Technical University of Munich using a Gas-Filled Analyzing Magnet System (GAMS) and a 14 MV Tandem accelerator is greatly effective in suppressing this interference. In the present study, the GAMS setup is used for the analysis of 99Tc in samples of the seawater reference material IAEA-443, a peat bog lake, and groundwater from an experiment of in situ diffusion through bentonite in the controlled zone of the Grimsel Test Site (GTS) within the Colloid Formation and Migration (CFM) project. With an adapted chemical preparation procedure, measurements of 99Tc concentrations at the fg/g levels with a sensitivity down to 0.5 fg are accomplished in notably small natural water samples. The access to these low concentration levels allows for the long-term monitoring of in situ tracer tests over several years and for the determination of environmental levels of 99Tc in small samples.

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Section: Analytical Techniquesmentioning

confidence: 94%

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confidence: 99%

Ultratrace Determination of ⁹⁹Tc in Small Natural Water Samples by Accelerator Mass Spectrometry with the Gas-Filled Analyzing Magnet System

et al. 2019

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“…This expectation is belied, in part, by the observation of measurable Tc profiles in natural sediments, ranging in depositional environments from marine, to terrestrial through transitional. This observation has stimulated numerous studies that investigate the mobility and fate of technetium in sediments (e.g., Aarkrog et al., 1997; Peretrukhin et al, 1996; Morris et al, 2000; Keith-Roach et al, 2003; Keith-Roach and Roos, 2004; Burke et al, 2006; Jenkinson et al, 2014; German et al, 2003; Standring et al, 2002). − These studies show that once pertechnetate is transported below a critical redox boundary in water, reduction occurs, and the resulting Tc(IV) is readily bound to suspended particles. Typical K D (concentration of Tc on the mineral surface divided by its concentration in solution) values for Tc(IV) between suspended particles and seawater are 10 2 to 10 3 .…”

Section: Technetium Behavior In Sediments and Soilsmentioning

confidence: 99%

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Pearce

Icenhower²,

Asmussen

et al. 2018

ACS Earth Space Chem.

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Technetium (Tc) contamination remains a major environmental problem at nuclear reprocessing sites, e.g., the Hanford Site, Washington State, USA. At these site, Tc is present in liquid waste destined for immobilization in a waste form or has been released into the subsurface environment. The high environmental risk associated with Tc is due to its long half-life (213,000 years) and the mobility of the oxidized anionic species Tc(VII)O 4-. Under reducing conditions, TcO 4 is readily reduced to Tc(IV), which commonly exists as a relatively insoluble and therefore immobile, hydrous Tc oxide (TcO 2 •nH 2 O). The stability of Tc(IV) sequestered as solid phases depends on the solubility of the solid and susceptibility to re-oxidation to TcO 4-, which in turn depend on the (bio-geo)chemical conditions of the environment and/or nuclear waste streams. Unfortunately, the solubility of crystalline TcO 2 or amorphous TcO 2 •H 2 O is still above the maximum contaminant level (MCL) established by the US EPA (900 pCi/L), and the kinetics of TcO 2 oxidative dissolution can be on the order of days to years. In addition to oxygen, sulfur can form complexes that significantly affect the adsorption, solubility and re-oxidation potential of Tc, especially Tc(IV). The principal technetium sulfides areTcS 2 and Tc 2 S 7 but much less is known about the mechanisms of formation, stabilization and re-oxidation of Tc sulfides. A common assumption is that sulfides are less soluble that their oxyhydrous counterparts. Determination of the molecular structure of Tc 2 S 7 in particular has been hampered by the propensity of this phase to precipitate as an amorphous substance. Recent work indicates that the oxidation state of Tc in Tc 2 S 7 is Tc(IV), in apparent contradiction to its nominal stoichiometry. Technetium is relatively immobile in reduced sediments and soils, but in many cases the exact sink for Tc has not been identified. Experiments and modeling have demonstrated that both abiotic and biologic mechanisms can exert strong controls on Tc mobility and that Tc binding or uptake into sulfide phases can occur. These and similar investigations also show that extended exposure to oxidizing conditions results in transformation of sulfide-stabilized Tc(IV) to a Tc(IV)O 2-like phase without formation of measurable dissolved TcO 4-, suggesting a solid-state transformation in which Tc(IV)-associated sulfide is preferentially oxidized before the Tc(IV) cation. This transformation of Tc(IV) sulfides to Tc(IV) oxides may be the main process that limits remobilization of Tc as Tc(VII)O 4-. The efficacy of the final waste form to retain Tc also strongly depends on the ability of oxidizing species to enter the waste and convert Tc(IV) to Tc(VII). Many waste form designs are reducing (e.g., cementitious waste forms such as salt stone), therefore, attempt to restrict access of oxidizing species such that diffusion is the ratelimiting step in remobilization of Tc.

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“…Pertechnetate (TcO 4 – ), the oxidized anionic form of radionuclide technetium-99 ( 99 Tc), has an international reputation for eluding retention by nuclear waste treatment technologies and for being extremely mobile in natural environments. Produced at high yield (∼6%) during thermal fission of uranium-235 and plutonium-239, 99 Tc persists primarily as TcO 4 – within millions of gallons of nuclear waste stored at legacy sites, including the Hanford (Washington State, USA) and Sellafield (Cumbria, UK) Sites. − Once in the environment, TcO 4 – rarely participates in sorption reactions with the surrounding sediment that would typically capture other radionuclides because of its low negative charge. As such, the environmental risks alone imposed by 99 Tc solubility and environmental mobility, then combined with its long half-life ( 99 Tc = 2.1 × 10 5 yr), make 99 Tc a primary contaminant of concern for immobilization and long-term storage.…”

Section: Introductionmentioning

confidence: 99%

Immobilizing Pertechnetate in Ettringite via Sulfate Substitution

Saslow

Kerisit

Varga

et al. 2020

Environ. Sci. Technol.

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Technetium-99 immobilization in low-temperature nuclear waste forms often relies on additives that reduce environmentally mobile pertechnetate (TcO 4 − ) to insoluble Tc(IV) species. However, this is a short-lived solution unless reducing conditions are maintained over the hazardous life cycle of radioactive wastes (some ∼10,000 years). Considering recent experimental observations, this work explores how rapid formation of ettringite [Ca 6 Al 2 (SO 4 ) 3 (OH) 12 •26(H 2 O)], a common mineral formed in cementitious waste forms, may be used to directly immobilize TcO 4 − . Results from ab initio molecular dynamics (AIMD) simulations and solid-phase characterization techniques, including synchrotron X-ray absorption, fluorescence, and diffraction methods, support successful incorporation of TcO 4 − into the ettringite crystal structure via sulfate substitution when synthesized by aqueous precipitation methods. One sulfate and one water are replaced with one TcO 4 − and one OH − during substitution, where Ca 2+ -coordinated water near the substitution site is deprotonated to form OH − for charge compensation upon TcO 4 − substitution. Furthermore, AIMD calculations support favorable TcO 4 − substitution at the SO 4 2− site in ettringite rather than gypsum (CaSO 4 •2H 2 O, formed as a secondary mineral phase) by at least 0.76 eV at 298 K. These results are the first of their kind to suggest that ettringite may contribute to TcO 4 − immobilization and the overall lifetime performance of cementitious waste forms.

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An estimate of the inventory of technetium-99 in the sub-tidal sediments of the Irish Sea

Cited by 14 publications

References 15 publications

Ultratrace Determination of ⁹⁹Tc in Small Natural Water Samples by Accelerator Mass Spectrometry with the Gas-Filled Analyzing Magnet System

Ultratrace Determination of ⁹⁹Tc in Small Natural Water Samples by Accelerator Mass Spectrometry with the Gas-Filled Analyzing Magnet System

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Immobilizing Pertechnetate in Ettringite via Sulfate Substitution

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An estimate of the inventory of technetium-99 in the sub-tidal sediments of the Irish Sea

Cited by 14 publications

References 15 publications

Ultratrace Determination of 99Tc in Small Natural Water Samples by Accelerator Mass Spectrometry with the Gas-Filled Analyzing Magnet System

Ultratrace Determination of 99Tc in Small Natural Water Samples by Accelerator Mass Spectrometry with the Gas-Filled Analyzing Magnet System

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Immobilizing Pertechnetate in Ettringite via Sulfate Substitution

Contact Info

Product

Resources

About

Ultratrace Determination of ⁹⁹Tc in Small Natural Water Samples by Accelerator Mass Spectrometry with the Gas-Filled Analyzing Magnet System

Ultratrace Determination of ⁹⁹Tc in Small Natural Water Samples by Accelerator Mass Spectrometry with the Gas-Filled Analyzing Magnet System