Gaseous Iodine Research Articles

Adsorption of iodine on metal coupons in humid and dry environments

In this study, five different metal coupons were evaluated for gaseous iodine [I 2(g) ] adsorption including two stainless steels (i.e., SS304 and SS316), two Inconel alloys (i.e., 625 and 718) and pure Ni (i.e., Ni-200) within a dynamic flow-through system where temperature, iodine concentration, flow rate, atmosphere, and relative humidity were controlled. Humidity was shown to be critical to iodine adsorption on SS304, SS316, and Ni-200 at ambient temperatures. The results presented herein provide evidence that a moisture-mediated reaction is occurring. However, higher humidity levels decrease the adsorption, suggesting an ideal range of humidity for the highest corrosion potential in these metals. A comparison of the five metal substrates showed the highest I 2(g) adsorption in the following descending order: Ni-200 > SS304 > SS316 > 718 > 625. The Inconel 625 and 718 alloys were fairly inert to iodine adsorption under the conditions tested. Characterization of the coupons by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction of the Ni-200 coupon indicates that NiI 2 formed and flaked off the surface as a black powder. The SS304 and SS316 coupons showed evidence of extensive reactions with I 2(g) and formed a much more deliquescent corrosion product , which reacted with air when removed from the flow-through system for weighing on the analytical balance. A static system was also used to expose separate polished coupons to I 2(g) , which allowed for analysis of the corrosion layers via scanning electron microscopy. These findings assisted in predicting iodine adsorption behaviors on a variety of metal surfaces under near-ambient conditions.

Revaporization Behavior of Cesium and Iodine Compounds from Their Deposits in the Steam-Boron Atmosphere.

This paper presents our investigation on cesium and iodine revaporization from cesium iodide (CsI) deposits on stainless steel type 304L, which were initiated by boron and/or steam flow. A dedicated basic experimental facility with a thermal gradient tube (TGT) having a temperature range of 1000–400 K was used for simulating the phenomena. In the absence of boron, it was found that the initially deposited CsI at 850 K could be revaporized as CsI vapor/aerosol or reacted with the carrier gas and stainless steel (Cr2O3 layer) to form Cs2CrO4. The latter mechanism consequently released gaseous iodine that was later accumulated downstream. After introducing boron to the steam flow, a severe revaporization occurred. This, in addition to the revaporized CsI vapor/aerosol, was caused by cesium borate (Cs2B4O7 and CsB5O8) formation, which then largely released gaseous iodine that was capable of reaching the TGT outlet (<400 K). In the case of a nuclear severe accident, our study has demonstrated that an increase of gaseous iodine in the colder region of a reactor could occur after late release of boron or a subsequent steam flow after refloods of the reactor, thus posing its inherent risk once leaked to the environment.

Facile synthesis of novel Bi0-SBA-15 adsorbents by an improved impregnation reduction method for highly efficient capture of iodine gas

Development of high efficient adsorbents to capture iodine is of great significance for the active development of nuclear power. Herein, Bi0-SBA-15 was firstly synthesized and applied for capture of iodine gas. Bi0-SBA-15 materials were prepared by an improved impregnation reduction method. The benefit of this method was that the Bi0 nanoparticles with flocculent and spherical morphologies were loaded on the surface of SBA-15, which provide abundant active sites for iodine and improve the utilization rate of active sites, so as to attain a record high capture capacity (up to 925 mg/g within 60 min) and high stablitiy (91.2%) at 200 °C. The results demonstrated that the loading of Bi0 on the surface showed a significant impact on the structure of Bi0-SBA-15 and did greatly enhance the iodine capture. Furthermore, the high iodine capture capacity mainly derived from the chemical adsorption in the stable form of BiI3. The obtained Bi0-SBA-15 materials exhibited excellent aqueous and irradiation stability. Thus, the results indicated that the new and highly efficient Bi0-SBA-15 was a potential radioactive iodine gas capture material.

Study of the stability of CsI and iodine oxides (IOx) aerosols and trapping efficiency of small aerosols on sand bed and metallic filters under irradiation

The decomposition of deposited CsI and iodine oxides (IOx) aerosols deposited on sand bed and on a metallic filter has been pursued under irradiation at 120 °C. On the sand, it was found that CsI aerosols are decomposed by the irradiation and the temperature effect into an inorganic specie assumed to be molecular iodine. The temperature effect might be due to surface effects of the sand grains as CsI aerosols are usually stable at this temperature. IOx aerosols are expected to be well retained by the sand filter (DF > 100) as long as the sand height is high enough (>60 cm). IOx are also decomposed by the temperature and irradiation. The humidity is also expected to have a significant influence on their decomposition. On the metallic filter, despite both species are expected to be significantly decomposed, very few gaseous iodine release from the filter was observed. The gaseous iodine species produced by the aerosols decomposition is assumed to be quickly adsorbed on the steel wires even if a slow desorption is also expected.

Silver-phosphate glass matrix for iodine conditioning: From sorbent design to vitrification

A new route for the synthesis of silver-phosphate based sorbent beads as precursors of final iodine waste form is proposed here. This sorbent is used to entrap gaseous iodine produced during the reprocessing of spent nuclear fuels and to be directly transformed into materials composed of a silver phosphate glass phase considered as high efficient iodine containment matrix for long-term storage in deep geological repository. Using sacrificial organic template method (alginate) and well controlled calcination of the obtained silver phosphate grains materials, this innovative synthesis makes in-situ formation of metallic silver inside them. Ag0 then can easily entrap iodine when in contact with gaseous iodine. The obtained sorbent were tested for iodine trapping in static conditions. They showed great performances with a catch rate of 480 mg.g−1. The iodine-loaded sorbent were finally heat treated at 650 °C with an iodine loss lower than 3% wt. The resulted materials shows the presence of the expected silver phosphate glass matrix with a great iodine incorporation of 9% mol.

Uncertainty quantification study on gas phase iodine release from Fukushima Daiichi accident in unit 3

A significant amount of radioactive iodine was release to the environment during the accident in the Fukushima Daiichi nuclear power plant. In this numerical study, we used the IMPAIR 2.2 code to simulate the iodine release during containment venting from the suppression chamber gas space and drywell leakage from unit 3 of the power plant. The IMPAIR code was coupled to the Dakota software and uncertainty quantification study and sensitivity analysis of the simulations was performed. The results indicated that both molecular iodine and organic methyl iodide were formed in the water volumes of the plant, where it was transferred to the gas phase of the modeled structures. The sensitivity analysis indicated that the water pH was the most sensitive parameter on the gaseous iodine formation and release during the venting or leakage periods. Additionally, the water pH was shown to affect the speciation of the gas phase iodine. Overall, the simulations performed in this work showed that iodine volatilized from the contaminated water phase in the suppression chamber and the drywell of Fukushima Daiichi unit 3 have an important contribution to the iodine source term to the environment.

Numerical analysis for FP speciation in VERDON-2 experiment: Chemical re-vaporization of iodine in air ingress condition

In the late phase of severe accident in light water reactor nuclear power station, re-mobilization of fission products (FPs) has a significant impact on the source term because most portion of FPs is retained in reactor coolant system and/or containment vessel. Recently, VERDON-2 experiment showed noticeable re-vaporization, which was one of the re-mobilization phenomena, of iodine under air ingress condition, but this mechanism has not been identified yet. The present study numerically investigated the FPs behaviors in VERDON-2 experiment with the mechanistic FPs transport analysis code incorporating thermodynamic chemical equilibrium model in order to further understand nature for FPs behavior, especially iodine re-vaporization under air ingress condition. Consequently, this analysis reproduced the deposition profile of cesium, one of important FPs in the source term, along the thermal gradient tube (TGT) in the experiment, which revealed that cesium was transported as CsOH in early phase of FP release from fuel, and then formed Cs2MoO4 and Cs2Te after the release of molybdenum and tellurium was activated. Regarding iodine as another important FP, formation of CsI was predicted in steam condition. The CsI was transported and partly deposited and condensed onto the TGTs and other components of the VERDON facility. Under the air ingress condition, the present analysis showed the agreement for iodine re-vaporization in the experiment and revealed its mechanism; the deposits of iodide were chemical re-vaporized as molecular iodine (I2) gas by redox reaction with competitive elements such as molybdenum, chromium and tellurium.

Visualization of gaseous iodine adsorption on single zeolitic imidazolate framework-90 particles

Zeolitic imidazolate frameworks (ZIFs) are very useful as high-capacity iodine (I2) adsorbents. The adsorption performance is usually probed by measuring a statistical average property over an entire sample consisting of a large number of ZIF particles, leaving the interparticle heterogeneity information among individuals. Here we report a dark-field microscopy (DFM) method to visualize gaseous I2 adsorption on single ZIF-90 particles in situ and in real time. The adsorption of I2 is found to alter the scattering spectrum of ZIF-90 particles, inducing a distinct color change from bluewhite to yellow. According to correlating the adsorption amount of gaseous I2 with the change of B value from DFM images, we quantitatively image the adsorption process and estimate the related kinetic parameters at the single particle level. Single particle measurements clarify the large particle-to-particle heterogeneity in adsorption reactivity and significant adsorption activity improvement of ZIF-90 after introduction of linker defects, which provides a microscopic understanding of the structure-activity relationship. We further demonstrate the capacity of this strategy for studying gaseous I2 adsorption on single ZIF-91 particle as a derivative of ZIF-90 to illustrate the generality.

A DFT study of iodine interaction with nuclear reactor cooling system surfaces under severe accident conditions

A severe nuclear accident can lead to the release of radiotoxic iodine compounds in either aerosol form (e.g. metal iodides or iodine oxides) or gaseous form (e.g. organic iodide as CH3I or inorganic as I2) species. 131I is particularly dangerous because of its possible absorption by the human body especially by the thyroid. Gaseous iodine is mainly formed in the nuclear containment building, is dispersed in the case of outside releases and may contribute in short term to long-distance contamination. Metallic iodide species are mainly formed at high temperature and partly condensed on the walls of the reactor coolant system (RCS), the rest being either deposited on the RCS or transported to the containment building. In this paper, we study theoretically, in severe accidental conditions, the adsorption of the metallic iodides on the surface of the primary circuit which is composed of Fe or Cr oxides. At high coverage, AgI and CdI2 form networks on the surfaces of the RCS whereas at low coverage the molecules are isolated. This study, setting out from the stable adsorbates, investigates the chemical mechanisms leading to the iodine re-vaporization. The formation of I2(g) from adsorbed AgI or CdI2 is thermodynamically and kinetically possible on over-oxidized chromium surfaces. On alternative surfaces, the co-adsorption of an oxidant, OH● issued from the steam radiolysis, is necessary to form I2(g). This study tends to show that delayed releases of gaseous iodine are likely to happen from the deposited iodide.

Interaction between caesium iodide particles and gaseous boric acid in a flowing system through a thermal gradient tube (1030 K–450 K) and analysis with ASTEC/SOPHAEROS

The present work aimed at studying the interaction between caesium iodide particles and gaseous boric acid through a Thermal Gradient Tube (TGT) from 1023 K to 453 K under Ar/H2O. Particles size range of transported particles was measured by ELPI and the fraction of gaseous compounds by ICP-MS and UV–visible spectroscopy. Reaction between the two compounds was deduced by measuring a significant fraction of gaseous iodine at the outlet of the facility, representing more than 80% of the total iodine sampled at the outlet. The reaction rate was shown to be lower when the flow rate inside the facility was increased. Analysis with SOPHAEROS module of ASTEC code was performed. The ASTEC fission products models allowed performing the evaluation of the experimentally observed results for the analysis of the transport of pure compounds. However, the heterogeneous interaction between the caesium iodide particles and the gaseous boric acid was not reproduced, as the models are not taken into account in the version v2.1_1_6 of the ASTEC/SOPHAEROS module. The next step would be to identify the mechanism of the reaction by comparing the results with other studies and to determine the reaction rates. Then, a first development in SOPHAEROS would be to implement such phenomena.

Polyacrylonitrile Composites of Ag–Al–Si–O Aerogels and Xerogels as Iodine and Iodide Sorbents

Mechanically robust engineered sorbents were constructed by embedding Ag-loaded aerogels or xerogels in a polyacrylonitrile (PAN) matrix at 30 or 50 mass% loadings of gel in PAN. The processes for making the base gels, Ag-exchanging the base gels, and making the PAN-gel composite materials are described herein. The composite technology is very flexible for making hybrid sorbents using various inorganic or organic active sorbents. The PAN-gel composite materials were evaluated for iodine uptake in the form of gaseous iodine [I2(g)] at room temperature and at 150 °C as well as iodide (I–) at room temperature from simulated liquid nuclear wastes. The composites show high I2(g) uptake and high I– uptake (≥93 mass%) in simulated liquid secondary waste spiked with 5 mg L–1 I–. These results demonstrate the utility of these composite forms for iodine removal from contaminated gas and liquid streams.

Comprehensive comparison of bismuth and silver functionalized nickel foam composites in capturing radioactive gaseous iodine

Developing an efficient and cheap iodine sorbent is of great practical significance in the modern nuclear industry. In this work, novel bismuth and silver functionalized Ni foam composites as iodine sorption materials (Bi-Ni foam and Ag-Ni foam) were successfully prepared via a simple solvothermal method. Through a series of iodine sorption experiments and characterization methods, iodine capture properties and corresponding sorption mechanism were comprehensively compared and thoroughly revealed. The results show that the core-sheath structure formed by the solvothermal reaction can supply more active sites (Bi0 or Ag0 particles) for the contact of radioactive iodine gas, thereby improving the sorption capacity of sorbents. Compared with Ag-Ni foam (456 mg/g), Bi-Ni foam exhibits a higher iodine capture capacity (658 mg/g), whereas silver-based material has a faster sorption kinetics. Such excellent sorption performances were attributed to the chemical reaction between Bi0/Ag0 particles and iodine gas, generating stable BiI3/AgI. In addition, this type of sorbents inherits the external structure of the Ni foam skeleton, decreasing the physically sorbed iodine, and can be prepared in different shapes and sizes, which is of great practical significance.

Barbituric and thiobarbituric acid-based UiO-66-NH2 adsorbents for iodine gas capture: Characterization, efficiency and mechanisms

Efficient iodine gas capture is necessitated in many industries like spent nuclear fuel off-gas treatment in view of environmental protection and resource recycling. However, the adsorption efficiency and stability of the current adsorbents are limited. In the present work, efficient and stable barbituric and thiobarbituric acid-based UiO-66-NH2 adsorbents (i.e., UiO-66-NH-B.D and UiO-66-NH-T.D, respectively) have been synthesized by post-synthetic covalent modification. Characterization approaches, including SEM-EDS, TEM, XRD, FTIR, XPS, 1H NMR, TGA and BET, are used to obtain information on the properties and adsorption mechanisms of these metal-organic framework (MOF) adsorbents. The kinetics and mechanisms involved are studied in detail. The treatment efficiency and recyclability of the adsorbents are checked and compared with the adsorbents reported in previous works. The results show that the current adsorbents are potentially suitable for efficient iodine gas capture. High maximum iodine adsorption amount by UiO-66-NH-B.D and UiO-66-NH-T.D (1.17 and 1.33 g/g) was achieved under 75 °C. These new adsorbents are thermally stable for iodine adsorption and regenerated and reused with good performance. The adsorption mechanisms were revealed based on experimental results, indicating that iodine is adsorbed by both physisorption and chemisorption.

Stability and radioactive gaseous iodine-131 retention capacity of binderless UiO-66-NH2 granules under severe nuclear accidental conditions

In the present work, we aim to investigate the ability of the zirconium-based MOF-type compound UiO-66-NH2, to immobilize molecular gaseous iodine under conditions analogous to those encountered in an operating Filtered Containment Venting System (FCVS) line. Typically, the UiO-66-NH2 particles were exposed to 131I (beta and gamma emitters) and submitted to air/steam at 120 °C, under gamma irradiation (1.9 kGy h-1). In parallel to this experiment under simulated accidental conditions, the stability of the binderless UiO-66-NH2 granules under steam and gamma irradiation was investigated. In order to fit with the specifications required by typical venting systems, and to compare the efficiency of the selected MOF to porous materials commonly used by the industry, scale-up syntheses and UiO-66-NH2 millimetric-size shaping were realized. For this task, we developed an original binderless method, in order to analyze solely the efficiency of the UiO-66-NH2 material. The shaped MOF particles were then submitted separately to gamma irradiation, steam and temperature, for confirming their viability in a venting process. Their structural, textural and mechanical behaviors were characterized by the means several techniques including gas sorption, powder X-ray diffraction, infrared spectroscopy and crushing tests. Promising results were obtained to trap gaseous molecular iodine in severe accidental conditions.

Marine iodine emissions in a changing world.

Iodine is a critical trace element involved in many diverse and important processes in the Earth system. The importance of iodine for human health has been known for over a century, with low iodine in the diet being linked to goitre, cretinism and neonatal death. Research over the last few decades has shown that iodine has significant impacts on tropospheric photochemistry, ultimately impacting climate by reducing the radiative forcing of ozone (O3) and air quality by reducing extreme O3 concentrations in polluted regions. Iodine is naturally present in the ocean, predominantly as aqueous iodide and iodate. The rapid reaction of sea-surface iodide with O3 is believed to be the largest single source of gaseous iodine to the atmosphere. Due to increased anthropogenic O3, this release of iodine is believed to have increased dramatically over the twentieth century, by as much as a factor of 3. Uncertainties in the marine iodine distribution and global cycle are, however, major constraints in the effective prediction of how the emissions of iodine and its biogeochemical cycle may change in the future or have changed in the past. Here, we present a synthesis of recent results by our team and others which bring a fresh perspective to understanding the global iodine biogeochemical cycle. In particular, we suggest that future climate-induced oceanographic changes could result in a significant change in aqueous iodide concentrations in the surface ocean, with implications for atmospheric air quality and climate.

Novel bismuth-based electrospinning materials for highly efficient capture of radioiodine

Radioiodine is one of the main fission products in the nuclear industry. Due to its strong volatility and radiotoxicity, it must be filtered and purified before being released into the environment. In this work, we reported three novel bismuth-based iodine sorption materials coated with Bi and/or Bi2O3 on the surface of electrospinning carbon nanofibers (HT-Bi2O3-ESCNF, HT-Bi-Bi2O3-ESCNF and HT-Bi-ESCNF). These materials were obtained by adding a hydrothermal step on the basis of electrospinning, pre-oxidation and carbonization process. The benefit of hydrothermal load was that active sites appeared on the outer surface of the fiber, making the contact with iodine gas more convenient and effective, and was no longer restricted by the concentration of Bi3+ in the solution like before. Finally, iodine capture tests were also conducted on these three sorbents and the property changes were investigated before and after iodine exposure. The results showed that the coating on the surface of the fiber did greatly improve the iodine capture capacity, and elemental bismuth had a greater effective atomic utilization rate of iodine than bismuth oxide, whose sorption capacity reached a record high of 732 mg/g among all the bismuth-based sorbents. The capture mechanism was thoroughly elucidated by a combination of PXRD, SEM, TEM, BET, XPS, Raman spectra and TGA characterizations.

Correction to “Evaluation of Getter Metals in Na–Al–Si–O Aerogels and Xerogels for the Capture of Iodine Gas”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to “Evaluation of Getter Metals in Na–Al–Si–O Aerogels and Xerogels for the Capture of Iodine Gas”Brian J. Riley*Brian J. RileyMore by Brian J. Rileyhttp://orcid.org/0000-0002-7745-6730, Saehwa ChongSaehwa ChongMore by Saehwa Chong, Matthew J. OlsztaMatthew J. OlsztaMore by Matthew J. Olszta, and Jacob A. PetersonJacob A. PetersonMore by Jacob A. PetersonCite this: ACS Appl. Mater. Interfaces 2021, 13, 2, 3491Publication Date (Web):January 7, 2021Publication History Published online7 January 2021Published inissue 20 January 2021https://doi.org/10.1021/acsami.0c22940Copyright © 2021 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views420Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (501 KB) Get e-Alerts Get e-Alerts

A crystalline covalent organic framework embedded with a crystalline supramolecular organic framework for efficient iodine capture

A bicrystalline composite based on a triazine covalent organic framework (COF) and a bisbenzimidazole supramolecular organic framework (SOF) was prepared for the first time and used for adsorption of gaseous iodine.

Molecular iodine interactions with metal substrates: Towards the understanding of iodine interactions in the environment following a nuclear accident

In order to evaluate the potential impacts to the public from radioiodine in a nuclear event, it is vital to expand our understanding of the interaction of molecular iodine with various surfaces. There are many potential surfaces that iodine could interact with in and around a nuclear facility, including stainless steel. This study, carried out at ambient temperature, pressure and humidity, demonstrates the highly adsorptive nature of molecular iodine on two types of austenitic stainless steel, SS304L and SS316L. By using a novel approach which combines inductively coupled plasma-optical emission spectroscopy (ICP-OES) with surface energy dispersive X-ray spectroscopy (EDS) there is evidence of the formation of metal iodides that have not previously been verified or quantified. Samples exposed to gaseous molecular iodine formed an iodine containing corrosion product visible by scanning electron microcopy (SEM). Evaluation of the metals in the corrosion region using EDS was compared to a water leach of the same samples analyzed using ICP-OES. The combination of techniques provides indication of metal iodide formation with minor stainless-steel constituents including: NiI2, MnI2 and CrI2.

A nitrogen-rich covalent organic framework for simultaneous dynamic capture of iodine and methyl iodide

<h2>Summary</h2> The capture of radioiodine species during nuclear fuel reprocessing and nuclear accidents is crucial for nuclear safety, environmental protection, and public health. Previously reported emerging materials for iodine uptake cannot outperform commercial zeolites and active carbon under the practical dynamic scenario. Herein, we present a new design philosophy aiming at significantly enhanced specific host-guest interactions and obtain a nitrogen-rich covalent organic framework material by introducing a bipyridine group into the building block for the simultaneous capture of both iodine gas through enhanced electron-pair effect and organic iodide via the methylation reaction. These efforts give rise to not only an ultrahigh uptake capacity of 6.0 g g⁻¹ for iodine gas and a record-high value of 1.45 g g⁻¹ for methyl iodide under static sorption conditions but also, more importantly, a record-high iodine loading capability under dynamic conditions demonstrated from the breakthrough experiments.