Behavior Of Iodine Research Articles

Chemical form dependent iodine transfer from seawater into seaweed and abalone.

Nuclear fuel reprocessing plant releases several kinds of radioactive nuclides, mainly 3H and 129I, into the oceans. Radio iodine causes thyroid dose. Iodine accumulates in several marine species such as wakame and abalone, which are food materials. Therefore, an analysis of iodine behavior in the marine environment is important to assess the impact of 129I. Iodine in seawater exists mainly in two chemical forms: iodide (I-) and iodate (IO3-). Their environmental behaviors are different. Thus, understanding these behaviors is important to assess the environmental behavior of total iodine. In this study, iodate and iodide transfer between seawater and abalone (Haliotis discus hannai) with 125I tracer was observed.

Do red marine carbonates represent oxic environments? New understanding from the Upper Ordovician marine limestone in Tarim Basin, China

Marine red beds (MRBs), typically colored by Fe- and Mn-rich minerals, are often interpreted as indicators of bottom water oxygenation. However, their continuous formation requires long-term input of aqueous derived Fe-Mn oxides and/or stable sources of Fe2+ and Mn2+ ions, challenging the traditional concept of “red equals oxic environment.” This study investigates two coeval Upper Ordovician Sandbian MRB carbonate intervals in the Tarim Basin. Previous studies attributed the pigment origin to hematite. Th/U values and total rare earth element and yttrium (REY) contents increased in the MRB interval, indicating a terrestrial source of iron. Hematite was observed within the intercrystal pores of calcite precipitating from porewater, consistent with high Nicarb abundance and MREE-enriched bulge pattern in the red intervals. Both sections exhibit high Fecarb and Mncarb, pointing to substantial reductive dissolution of Fe and Mn oxides. Simulation shows that isotopic discrimination (Δ13C) between carbonate and organic carbon could be biased by increasing benthic Fe-Mn flux, leading to decreased Δ13C values in MRB intervals. Ce/Ce∗ values in the high-Mncarb interval reflect the releasing of Ce by reductive dissolution of Mn oxides. The commonly used carbonate-based redox proxy I/(Ca + Mg) ratio is correlated positively with Mncarb in the shallower section and with TOC in the deeper section, while it is negatively correlated with TOC in the shallower horizon, suggesting that iodine behavior may be influenced by adsorption and releasing of Mn hydro-oxides and organic matter besides oxygen contents. This study links MRB coloring to Fe and Mn mineral cycling in pore water through reductive dissolution and oxidative precipitation, and highlights potential biases of carbonate-based redox proxies that might be susceptible to other electron acceptors/donors such as Fe-Mn oxides and organic matter, in addition to free oxygen in seawater.

Pressure dependence of superconducting behavior of solid Br and I: A first-principles study

Based on the first-principles calculations, this study employs the HSE06 functional for the first time to understand the high-pressure behavior of diatomic molecular crystal bromine and iodine. It meticulously replicates the metallization process of iodine and bromine from aspects including bond length, charge density, band structure, and density of states. Furthermore, we also investigate the pressure-dependent superconducting properties of monoatomic phases of bromine and iodine, probing into the reasons behind the discrepancies in Tc values among different phases.

Review of iodine behavior from nuclear fuel dissolution to environmental release.

During nuclear fuel reprocessing, radioiodine, can be released. The speciation of iodine drives its volatility, and partitioning processes are highly variable because they depend on facility operating conditions. Starting from iodine behavior in the fuel and progressing to its behavior in the environment, this review article describes the current understanding of iodine partitioning during aqueous fuel reprocessing. This review outlines knowledge gaps and describes the effects of state-of-the-art reprocessing techniques on iodine speciation and volatility. Whereas many review articles have described iodine behavior during specific reprocessing steps, this review provides a holistic overview of radioiodine, from the forms of iodine in different types of irradiated fuel to the forms of iodine released into the environment. The resultant behavior of radioiodine compared with stable iodine in the environment is also described.

Iodine source term assessment as result of iodine spiking and mass transfer phenomena during a SGTR transient using MELCOR 2.2 and CATHARE 2 codes

The European project denominated Reduction of Radiological Consequences of design basis and design extension Accidents (R2CA) was launched in September 2019, with a very broad participation: 11 countries, 17 participating organisations, including international organisations, utilities, regulators, technical support organisations, researchers and developers and was coordinated by IRSN. The main goal of the project was to assess the conservatisms in the radiological releases calculations in nuclear power plant (NPP) studies.The work here presented is focused on developing new calculation methodologies and updating computer code models to carry out more detailed assessments of source terms resulting from a steam generator tube rupture (SGTR) accident in the Design Extension conditions A (DEC-A) domain. For this purpose, participants in Work Package 2 (WP2) of R2CA developed and implemented simplified models in the Severe Accident (SA) and Thermal-Hydraulic (TH) codes that take into account iodine spiking and iodine transport phenomena within primary and secondary circuit. These methodologies will not only provide a better estimation of the radiological consequences, but should also serve to improve accident management procedures, innovative instrumentation development and early detection tools.The new approaches are tested in a SGTR + Steam Line Break Outside Containment scenario without significant fuel degradation in a three-loop Western 1000 MWe PWR. During the transient, operators are also assumed to implement emergency operating procedures (EOPs) in line with Westinghouse EOPs to limit the release of radioactivity and control the evolution of plant parameters.The calculations are performed by Tractebel and CIEMAT with the American SA tool MELCOR and Bel-V with the French TH code CATHARE.The results highlighted some limitations of implemented models in predicting iodine behaviour as well as small discrepancies in the TH evolution of the transient, both of which were analysed and discussed in detail.

An analytical model to decompose mass transfer and chemical process contributions to molecular iodine release from aqueous phase under severe accident conditions

Radioactive iodine is a representative fission product to be quantified for the safety assessment of nuclear facilities. In integral severe accident analysis codes, the iodine behavior is usually described by a multi-physical model of iodine chemistry in aqueous phase under radiation field and mass transfer through gas-liquid interface. The focus of studies on iodine source term evaluations using the combination approach is usually put on the chemical aspect, but each contribution to the iodine amount released to the environment has not been decomposed so far. In this study, we attempted the decomposition by revising the two-film theory of molecular-iodine mass transfer. The model involves an effective overall mass transfer coefficient to consider the iodine chemistry. The decomposition was performed by regarding the coefficient as a product of two functions of pH and the overall mass transfer coefficient for molecular iodine. The procedure was applied to the EPICUR experiment and suppression chamber in BWR.

Diffusion Behavior of Iodine in the Micro/Nano-Porous Graphite for Nuclear Reactor at High Temperature

The diffusion behavior of iodine in micro/nano-porous graphite under high-temperature conditions was studied using analysis methods such as Rutherford backscattering Spectrometry, scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The results indicate that iodine diffusion leads to the Lattice Contractions in Microcrystals, a decrease in interlayer spacing, and a rise of defect density. And the reversal or repair of microstructure change was observed: the microcrystal size of the graphite increases, the interlayer spacing appears to return to the initial state, and the defect density decreases, upon diffusion of iodine out of iodine-loaded graphite. The comparative study comparing the iodine diffusion performance of nanoporous graphite (G400 and G450) between microporous graphite (G500), showed that nanoporous graphite exhibits a better barrier to the iodine diffusion. The study on the diffusion behavior of iodine in micro/nano-porous graphite holds substantial academic and engineering value for the screening, design, and performance optimization of nuclear graphite.

Construction of camphor leaves-derived biochar@bismuth for the capture of gaseous iodine

Herein, Bi2O3 loaded with camphor leaves-derived biochar (Bi2O3@CLBC) was prepared to capture gaseous iodine. Bi2O3@CLBC was provided with a loose structure, high reactivity and relatively good thermal stability, leading to a high uptake capacity. The capture behavior of iodine on Bi2O3@CLBC was well described by the Pseudo-first-order and Langmuir models, demonstrating the occurrence of monolayer chemisorption on Bi2O3@CLBC. The maximum adsorption amount of Bi2O3@CLBC for iodine was 885.8 mg/g. The chemical uptake played a leading role in capturing volatile iodine, including the direct reaction between Bi2O3 particles and iodine vapor and the charge transfer between the –OH on biochar and iodine to generate a coordination complex. The pores on the surface of biochar could also capture some iodine through physical adsorption. In one word, this work was expected to offer a green treatment method for the excess of camphor leaves and an exceptional adsorbent for iodine uptake from spent fuel.

Study on the mechanical strength and iodine adsorption behavior of coal-based activated carbon based on orthogonal experiments

To prepare coal-based activated carbon with high mechanical strength and adsorption performance for the removal of iodine from wastewater, the effects of carbonization temperature, heating rate, activation time and activator on the mechanical strength of activated carbon were studied; the optimal production conditions were determined by comprehensively considering the specific surface area, iodine value, compressive strength and wear resistance based on previous studies. Iodine adsorption kinetics and equilibrium adsorption experiments were carried out on activated carbon prepared under the optimum conditions. The results showed that the increase in mechanical strength was caused by the release of volatile matter and secondary reactions, which formed the carbon skeleton, while the decrease in mechanical strength was due to the intervention of the activator, which destroyed the carbon skeleton. The adsorption kinetics showed that a pseudo-second order kinetic model was more suitable for the adsorption behavior of iodine on activated carbon. The equilibrium adsorption experiment results showed that iodine was evenly adsorbed on the surface of activated carbon, and with increasing temperature, the affinity of the active sites of activated carbon to iodine also increased.

Triple-halogen (Cl-Br-I) fluid inclusion LA-ICP-MS microanalysis to unravel iodine behavior and sources during marine fluid infiltration into the basement in unconformity settings

Halogen signatures of hydrothermal fluids are a powerful tool for deciphering fluid provenance and reconstruction of key ore-forming mechanisms such as fluid mixing processes. Analytical protocols for LA-ICP-MS fluid inclusion analysis of Cl and Br concentrations have existed for over 10 years, but Br/Cl ratios alone do not provide unambiguous evidence of fluid provenance. However, recent methodological advances now allow also for quantification of I by LA-ICP-MS analysis in single fluid inclusions, significantly expanding the applicability of halogens for unambiguous fluid provenance analysis. However, owing to the novelty of the fluid inclusion triple-halogen LA-ICP-MS method, and due to the notorious difficulties caused by the generally low I concentrations in hydrothermal fluids, reference Cl-Br-I data of many crustal fluid types remains scarce, even when including data from bulk analytical techniques. Single fluid inclusion halogene analytics as are used here are vital due to the lack of sampling bias inherent to bulk analytical techniques that narrow the analyzed compositional range.The evaluation of Cl, Br and I systematics of fluid inclusions from unconformity-related hydrothermal veins in the Schwarzwald, Germany, provides new insight into the behavior of I and the evolution and source of the fluids involved in formation of unconformity-type vein deposits in central Europe during the Triassic to Cretaceous. While the variation in Br/Cl (molar ratio: 0.1 × 10−3–8.3 × 10−3) is consistent with previously established models of mixing processes between two fluids with a salinity source in seawater evaporation (modified bittern brine) and halite dissolution (modified halite dissolution brine), respectively, the large scattering of I/Cl (molar ratio: 1.4 × 10−6–330 × 10−6) cannot be attributed to the salinity source alone. Instead, I must have been derived from interaction with organic matter, which appears to have been more pronounced within the modified bittern brine fluid endmember. During fluid infiltration into the basement and associated fluid-rock interaction, I/Cl and Br/Cl acted conservatively on analytically detectable scales and large inhomogeneities in source I signatures remained intact. This finding also presents direct evidence of local fluid composition inhomogeneity and absence of internal mixing of basement reservoirs for long time periods (more than 100 Ma).

Coupled global and PIC modelling of the REGULUS cathode-less plasma thrusters operating on xenon, iodine and krypton

In recent years, the increasing demand for simple and low-cost propulsion for small satellites has given rise to a growing interest in low-power cathode-less plasma thrusters. Plasma is produced within a source tube using radiofrequency (RF) ionisation, enhanced by a magnetic field which also accelerates the discharge via the magnetic nozzle effect. A key advantage of cathode-less thrusters is that they can operate on a wider range of propellants, more easily stored, and often inexpensive (e.g., iodine) compared to traditional xenon. Despite simple hardware, plasma dynamics in this kind of device are highly complex. This work presents a numerical suite developed for cathode-less plasma thruster design and analysis. First, a 0D Global Source Model provides the plasma production in the source. A fully kinetic Particle-in-Cell model (2D and 3D) then handles plasma expansion in the magnetic nozzle. The capabilities of the suite are presented by-way-of investigation into the behaviour of alternative propellants iodine and krypton within the 50 and 150 W class REGULUS thrusters. The performance of each propellant is assessed in terms of plasma source and magnetic nozzle efficiencies. The results are then benchmarked against experimental measurements, obtaining agreement of <30%. At absorbed powers <20 W, iodine exhibits comparable performance to xenon but produces about 50% less thrust as the power is increased above 40 W. This occurs because of the molecular reaction processes seen by iodine, and associated inelastic energy thresholds which result in higher collisional energy losses. The high ionisation energy of krypton results in a low source efficiency. Instead, in the magnetic nozzle, krypton was found to perform best, facilitating the most thermal-to-kinetic conversion. But, the final thrust is <20% of xenon; instead iodine performs within 43% of the thrust provided by xenon. Finally, iodine contamination of spacecraft surfaces is found to be comparable to estimates found in other electric propulsion devices.

THAI experiments on iodine behavior in a room chain representing flow conditions in large containments

Iodine which can be released into the containment during a severe accident, is considered one of the most important nuclides with potential for public dose. Significantly different iodine concentrations can be expected in the individual compartments and rooms of large containments, due to geometrical constraints and the strong dependence of many iodine reactions on local thermohydraulic conditions. Such inhomogeneity may be relevant for organic iodide formation which depends on the concentration of deposited I2 and the dose rate.The objective of the two tests Iod-33 and Iod-35 was to measure the distribution of iodine along a convective flown-through room chain. This arrangement shall simulate the pathway of iodine from the locations of release (primary loop rupture) or formation (sump) along the plant rooms up to the dome of the containment and back. With respect to iodine, the aims were to measure the distribution and mixing of gaseous iodine in different rooms, the decrease of gaseous iodine by its deposition on painted surfaces, and the distribution of deposited iodine on the different painted surfaces.The two tests were performed in the two vessel THAI+ facility with additionally installed painted surfaces (painted with Gehopon epoxy paint) under superheated and condensing conditions. The main part of the painted surface area was provided in the form of painted steel sheets and arranged to form two intermediate floors within the THAI test vessel including small flow openings. Gaseous iodine was injected over several hours into the room chain in which a slow convection was established by means of differential wall heating.The gaseous I2 concentration inside the THAI+ facility increased continuously until the I2 injection was terminated. Simultaneously, the iodine deposition onto the painted surface increased. The gaseous I2 concentration decreased rapidly after stopping the I2 injection, in favor of a continuation of the I2 deposition on painted surfaces. The multi-compartment effect along the room chain has been demonstrated by the test results and the data allows for further development and validation of the I2/paint reaction model of severe accident codes.

Environmental iodine speciation quantification in seawater and snow using ion exchange chromatography and UV spectrophotometric detection

The behaviour and distribution of iodine in the environment are of significant interest in a range of scientific disciplines, from health, as iodine is an essential element for humans and animals, to climate and air quality, to geochemistry. Aquatic environments are the reservoir for iodine, where it exists in low concentrations as iodide, iodate and dissolved organic iodine and in which it undergoes redox reactions. The current measurement techniques for iodine species are typically time-consuming, subject to relatively poor precision and require specialist instrumentation including those that require mercury as an electrode. We present a new method for measuring iodine species, that is tailored towards lower dissolved organic carbon waters, such as seawater, rainwater and snow, using ion exchange chromatography (IC) with direct ultra-violet spectrophotometric detection of iodide and without the need for sample pre-concentration. Simple chemical amendments to the sample allow for the quantification of both iodate and dissolved organic iodine in addition to iodide. The developed IC method, which takes 16 min, was applied to contrasting samples that encompass a wide range of aqueous environments, from Arctic sea-ice snow (low concentrations) to coastal seawater (complex sample matrix). Linear calibrations are demonstrated for all matrices, using gravimetrically prepared potassium iodide standards. The detection limit for the iodide ion is 0.12 nM based on the standard deviation of the blank, while sample reproducibility is typically <2% at >8 nM and ∼4% at <8 nM. Since there is no environmental certified reference material for iodine species, the measurements made on seawater samples using this IC method were compared to those obtained using established analytical techniques; iodide voltammetry and iodate spectrophotometry. We calculated recoveries of 102 ± 16% (n = 107) for iodide and 116 ± 9% (n = 103) for iodate, the latter difference may be due to an underestimation of iodate by the spectrophotometric method. We further compared a chemical oxidation and reduction of the sample to an ultra-violet digestion to establish the total dissolved iodine content, the average recovery following chemical amendments was 98 ± 4% (n = 92). The new method represents a simple, efficient, green, precise and sensitive method for measuring dissolved speciated iodine in complex matrices.

Enhancing performance of organic-inorganic perovskite solar cells using super halogen additive

Compositional engineering in perovskite solar cells usually uses mixed cations and halide anions to optimize the growth of perovskite films, reduce film defects and inhibit carrier recombination to achieve high-performance devices. The most commonly used anion component of perovskite is the iodine ion. However, the ionic behavior of iodine greatly affects the stability of perovskite solar cell devices. Here, NaBF 4 was first used to partially replace iodine in perovskite CS 0.05 (FA 0.92 MA 0.08 ) 0.95 Pb(I 0.92 Br 0.08 ) 3 . After doping NaBF 4 , perovskite films show a longer PL lifetime and greater recombination resistance. It is found that the Stokes shift of the PL peak of the target film is reduced, indicating that doping NaBF 4 significantly inhibits the non-radiative recombination in the perovskite film. Doping NaBF 4 in perovskite passivates its defects, significantly improves the open-circuit voltage, filling factor and the power conversion efficiency of the device from 18.31% of the original device to 20.63%. After being stored in a nitrogen environment for 2400 hours, the device efficiency remains unchanged. • A super halogen BF 4 − anion is used to partially replace iodine ion to fine tune the perovskite components. • The efficiency of perovskite solar cell is increased from 18.31% to 20.63%. • After being stored in a nitrogen environment for 2400 hours, the device efficiency remains unchanged.

Ultra-Sensitive Determination of Particulate, Gaseous Inorganic and Organic Iodine-129 and Iodine-127 in Ambient Air.

Atmospheric iodine cycling is of significance in climate change and environmental and health impacts. To better explore speciation transformation of atmospheric stable and radioactive iodine, an ultra-sensitive analytical method was established for determination of 129I and 127I in particulate, gaseous inorganic, and gaseous organic species, which was conducted with a self-designed cascade sampling apparatus, followed by their separation with a pyrolysis system and accelerator mass spectrometry and ICP-MS measurements. Combustion protocols for three sampling matrices and NaOH concentration for iodine trapping were optimized to achieve a safe analytical procedure with a high chemical yield of iodine. Based on the lowest concentrations of 129I and 127I, a suitable activated carbon product for adsorption of gaseous organic iodine was carefully selected. The detection limits of the three species were 0.30-2.21 ng m-3 for 127I and 0.05-0.22 × 105 atoms m-3 for 129I. This newly established method was successfully applied to analyze the levels and species of 129I and 127I in ambinet air from Xi'an, China, from May to August, 2020. Gaseous organic iodine was found to be the dominant species of 127I and 129I, accounting for about half of total iodine, and gaseous inorganic iodine and particulate iodine accounted for one-quarter each during the whole sampling period. Speciation variation of 129I and 127I indicates that speciation transformation apparently occurred at the turn of spring and summer, mainly between particulate and gaseous organic iodine. This study has implications on delicate tracing of the atmospheric behavior of iodine with long-lived anthropogenic 129I.

Hydrogen Deflagration Analysis in THAI Experiments Using MELCOR Code

Abstract The Research Center Řež (CVŘ) is developing a methodology to simulate nuclear power plants under accidental conditions. A particular effort is focused in the severe accident phenomenology where hydrogen deflagration carries a critical issue for the containment integrity, such as Fukushima Daiichi accident. For this purpose, the Thermal-hydraulics, hydrogen, aerosol and iodine (THAI) experimental campaigns are chosen due to the several tests involved in different conditions. THAI containment test facility is used to open questions concerning the behavior of hydrogen, iodine, and aerosols in the containment of water-cooled reactors during severe accidents.The Fukushima Daiichi Accident demonstrates that the hydrogen deflagration could lead to a significant containment damage. For this reason, a particular attention is given to the hydrogen deflagration scenario. All simulations are prepared and modeled in melcor 2.1. The results obtained showed a strong influence related to some factors such as: the nodalization pattern, control volumes (CVs) number, flow paths (FPs) number, and time-step. In order to assess the THAI model with the THAI final reports, a sensitivity analysis focused on those parameters was performed, which developed four different models with different nodalization.

Analyses on importance of iodine chemistry models in AnCheBi code for a severe accident of nuclear power plant

In this paper, with the experimental data on the chemical behavior of iodine under the conditions of severe accident in nuclear power plant, first, we perform numerical analyses on the iodine chemistry model in AnCheBi (Analysis on Chemical Behavior of Iodine Species in the Containment) code for validation. Then, we perform analyses on the importance of the iodine chemistry models in AnCheBi code. In the analyses, the reaction coefficients are randomly sampled via Latin Hypercube sampling. The correlation coefficients, then, are calculated via the results of sensitivity analyses of AnCheBi with the randomly sampled reaction coefficients. In the calculations of correlation coefficients, concentrations of the iodine species are selected as figure of merits. From the correlation coefficients, we provide the reaction coefficients which are related with the dominant phenomena among the various chemical behaviors of iodine. Hence, they are the most important to evaluate the source term of nuclear accident in terms of regulatory view.

The behavior of iodine in stabilized granular activated carbon and silver mordenite in cementitious waste forms

Both granular activated carbon (GAC) and silver mordenite (AgM) are utilized for the removal of contaminants and radionuclides (e.g., radioiodine) from off-gas streams in nuclear fuel reprocessing and high temperature immobilization of nuclear waste. Following their service lifetimes, the GAC and AgM contain an inventory of contaminants and radionuclides and require stabilization in a matrix for disposal. GAC and AgM are referred to as solid secondary waste (SSW) materials. Cementitious waste forms can be used as the stabilization matrix for SSW, however, for successful stabilization, the inclusion of GAC and AgM should not negatively impact the physical behavior of the cementitious waste form or increase release of the contaminants/radionuclides compared to the baseline case without stabilization. The present work focuses on evaluation of cement formulations, with and without slag, for the stabilization of iodine-loaded GAC or AgM. The results showed that both a slag-containing and slag-free formulations were able to stabilize GAC and AgM, up to 30 vol%, without deleterious impacts on the bulk physical properties of the encapsulating matrix. When monolithic samples of the GAC or AgM containing cement formulations were subjected to leach tests, it was observed that iodide leached from the SSW) had limited sorption to either of the cement matrices. Nonetheless, the iodine can interact with the SSW materials themselves. Specifically, iodine retention within monolithic samples containing the iodine-loaded GAC or AgM was improved for AgM containing waste forms while no improvement was observed for the GAC containing waste forms. The improvement for the AgM containing waste forms was likely due to an enrichment of Ag at the interface between the AgM particles and the cement matrix that can impede iodine migration out from the waste form. The results are significant in highlighting the potential for long-term retention of iodine in specific cementitious waste forms.

1H-13C heteronuclear single quantum coherence NMR evidence for iodination of natural organic matter influencing organo-iodine mobility in the environment

The complex biogeochemical behavior of iodine (I) isotopes and their interaction with natural organic matter (NOM) pose a challenge for transport models. Here, we present results from iodination experiments with humic acid (HA) and fulvic acid (FA) using 1H-13C heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) spectroscopy. Even though not a quantitative approach, 1H-13C HSQC NMR corroborated that iodination of NOM occurs primarily through aromatic electrophilic substitution of proton by I, and also revealed how iodination chemically alters HA and FA in a manner that potentially affects the mobility of iodinated NOM in the environment. Three types of iodination experiments were conducted with HA and FA: a) non-enzymatic iodination by IO3− (pH 3) and I− (pH 4 and 7), b) addition of lactoperoxidase to promote I−-iodination in the presence of the co-substrate, H2O2 (pH 7), and c) addition of laccase for facilitating I−-iodination in the presence of O2, with or without a mediator (pH 4). When mediators or H2O2 were present, extracellular oxidases and peroxidases enhanced I− incorporation into NOM by between 54% and 3400%. Iodination of HA, which was less than that of FA, enhanced HA's stability (inferred from increases in aliphatic compounds, decreases in carbohydrate moieties, and thus increased molecular hydrophobicity) yet reduced HA's tendency to incorporate more iodine. As such, HA is expected to act more as a sink for iodine in the environment. In contrast, iodination of FA appeared to generate additional iodine binding sites, which resulted in greater iodine uptake capability and enhanced mobility (inferred from decreases in aliphatic compounds, increases in carbohydrates, and thus decreases in molecular hydrophobicity). These results indicate that certain NOM moieties may enhance while others may inhibit radioiodine mobility in the aqueous environment.

Iodine release from high-burnup fuel structures: Separate-effect tests and simulated fuel pellets for better understanding of iodine behaviour in nuclear fuels

Iodine release modelling of nuclear fuel pellets has major uncertainties that restrict applications in current fuel performance codes. The uncertainties origin from both the chemical behaviour of iodine in the fuel pellet and the release of different chemical species. The structure of nuclear fuel pellet evolves due to neutron and fission product irradiation, thermo-mechanical loads and fission product chemical interactions. This causes extra challenges for the fuel behaviour modelling. After sufficient amount of irradiation, a new type of structure starts forming at the cylindrical pellet outer edge. The porous structure is called high-burnup structure or rim structure. The effects of high-burnup structure on fuel behaviour become more pronounced with increasing burnup. As the phenomena in the nuclear fuel pellet are diverse, experiments with simulated fuel pellets can help in understanding and limiting the problem at hand. As fission gas or iodine release behaviour from high-burnup structure is not fully understood, the current preliminary study focuses on (i) sintering of porous fuel samples with Cs and I, (ii) measurements of released species during the annealing experiments and (iii) interpretation of the iodine release results with the scope of current fission gas release models.Graphical abstract