Off-gas Stream Research Articles

An efficient Ni-based adsorbent for selective removal of 85Kr and 14CH4 in radioactive contaminants from nuclear process off-gas stream

Efficient adsorbents for radioactive gas treatment in nuclear energy cycle is crucial for eliminating negative environmental impacts caused by wide nuclear applications. A Ni-based MOF material called JUC-86(Ni) which is based on 1-H-benzimidazole-5-carboxylic acid (HBIC) linker was synthesized for adsorbing the 85Kr, 14CH4 from off-gas stream. It was disclosed that there is a suitable pore environment for 85Kr and 14CH4 preferred adsorption in JUC-86 and the adsorption capacity could even reach 2.79 mmol/g (85Kr) and 2.54 mmol/g (14CH4) which are almost higher than all the adsorbents. The 85Kr/N2 and 14CH4/N2 IAST selectivities of the resulting sample are satisfactory (11.63 and 9.43) and well matched with the breakthrough experiments where the breakthrough times of 85Kr and 14CH4 are much longer than N2. What’s more, the adsorption heats of 85Kr and 14CH4 are less than 30 kJ/mol which indicated a stronger affinity than N2 and a low-energy regeneration. As simulation results showed that the adsorption distribution follows a-spiral-pattern which could be attributed to the N atom in the CN, this is also the dominant factor of the 85Kr and 14CH4 preferable adsorption.

Bimetallic Fe–Cu metal-organic frameworks for capturing of radioactive iodine in solution and vapor phases

Effectively removing radioactive iodine from the environment is critical for mitigating the risks associated with nuclear accidents. This research presents a brand-new Fe-Cu-BTC metal-organic framework (MOF) composite that works very well to absorb iodine. We employed a facile one-pot solvothermal method to achieve epitaxial growth of Fe-BTC on a Cu-BTC substrate. A full analysis using SEM, EDS, FTIR, XRD, BET, TEM, XPS, Raman, and TGA/DTA showed that the composite was successfully made while the crystalline structure of the CuBTC was kept. It was amazing how well the Fe-Cu-BTC composite could absorb iodine, reaching maximum capacities of 217.92 mg/g in solution and 623.21 mg/g in vapor phases, respectively, within the time limits given. The material demonstrated remarkable stability and recyclability, retaining its structural integrity and efficiency over five consecutive adsorption-desorption cycles. The high BET surface area of 820.35 m/g, pore volume of 0.328 cm/g, and pore diameter of 2.950 nm of the composite contributes to its superior adsorption performance. The composite exhibits exceptional stability under acidic conditions with a pH of 2>8.Studies of the adsorption isotherm and kinetics showed that the Langmuir and pseudo-second-order models correctly describe how iodine binds, with R² values of 0.995 and 0.994, respectively. XPS and Raman spectroscopy with peak values (72.21, 104.4, and 167.04) cm-1 confirmed the formation of polyiodides (I₃⁻ and I₅⁻) on the MOF surface, suggesting a physical adsorption mechanism.The Fe-Cu-BTC composite has a controlled synthesis, millimeter-scale dimensions, a porous structure, is very stable, and can be recycled easily. It looks like it could be a good way to capture and store iodine from a variety of environmental sources, such as reprocessing plant off-gas streams and liquid effluents.

Hydrophobic nanosheet silicalite-1 zeolite for iodine and methyl iodide capture

Effective capture of radioactive iodine from nuclear fuel reprocessing is of great importance for public safety as well as the secure utility of nuclear energy. In this work, a hydrophobic nanosheet silicalite-1 (NSL-1) zeolite with an adjustable size was developed for efficient iodine (I2) and methyl iodide (CH3I) adsorption. The optimized all-silica zeolite NSL-1 exhibits an excellent I2 uptake capacity of 553 mg/g within 45 min and a CH3I uptake capacity of 262 mg/g within 1 h. Benefiting from the reduced thickness and enhanced porosity, microporous NSL-1 possesses enhanced iodine adsorption capacity and fast adsorption kinetics, which is a considerable high value among inorganic materials. Unexpectedly, the remarkable characters of high hydrophobicity, acid-resistance and anti-oxidation endow it a higher iodine uptake capacity than traditional aluminosilicate zeolites. More importantly, the high uptake selectivity toward I2 possessed by NSL-1 owing to its hydrophobic skeleton under simulated dynamic conditions. The low cost, facile and scalable synthesis of NSL-1 further highlights great prospects for applications in the nuclear industry. This work provides useful insights for designing efficient adsorbents for iodine capture.

Adsorption of Radioactive Iodine Using Nanocarbon on ETS-10 as Adsorbent

Laboratory-synthesized nanocarbon pelletized with titanosilicate (ETS-10) as a support matrix has been investigated for the capture of radioactive iodine present as methyl iodide (CH3I) in the off-gas streams produced during aqueous reprocessing of used nuclear fuel. The mass fraction of carbon in the sorbent matrix was 0.10. The effects of residence time and CH3I concentration were investigated using a continuous flow column setup to quantify the adsorption and desorption capacities of adsorbent under dynamic conditions from an air stream containing CH3I present at concentrations representative of those expected in the off-gas streams. Air with CH3I gas as a source in the column resulted in quantifiable CH3I adsorption with 0.98 mg/g of adsorption capacity. Laboratory-made nanocarbons had a larger adsorption capacity than those of the other carbons reported in the literature. Additionally, the adsorption capacity of nanocarbon on ETS-10 is compared to that of nanocarbon coated on cordierite in previous studies.

Development of a Nuclear Fuel Dissolution Monitor Based on Raman Spectroscopy.

The processing of spent nuclear fuel and other nuclear materials is a critical component of nuclear material management with implications for global security. The first step of fuel processing is dissolution, with several charges of fuel sequentially added to a batch of solvent. The incomplete dissolution of a charge precludes the addition of the next charge. As the dissolution takes place in a heated, highly corrosive and radiological vessel, direct monitoring of the process is not possible. We discuss the use of Raman spectroscopy to indirectly monitor dissolution through an analysis of the gaseous emissions from the dissolver. Challenges associated with the implementation of Raman spectroscopy include the composition and physical characteristics of the offgas stream and the impact of operating conditions. Nonetheless, we observed that NO2 concentrations serve as a reliable indicator of process activity and correlate to the amount of fuel material that remains undissolved. These results demonstrate the promise of the method for monitoring nuclear material dissolution.

A hydroxy containing, naphthalene-based and imine linked porous organic polymer for rapid iodine uptake

Nuclear energy is turning out to be one of the best alternatives to fossil fuels in order to meet the global electricity demand. Radioactive iodine is a volatile and hazardous component that may be present in aqueous nuclear waste and off-gas streams of a spent fuel processing plant. Iodine species are also quite mobile and their accidental leakage into the environment can adversely affect the health of animals and humans to an alarming extent. Thus, design and development of materials capable of capturing/storing iodine effectively for a long time, is of utmost importance in contemporary research. Herein, facile synthesis of a unique nitrogen rich and thermally stable porous organic polymer (POP_DH) is described that has a porous structure comprising of both micro and mesopores. The POP_DH has a specific surface area (128.3 m2 g-1), and can capture 2.855 g g−1 of iodine (vapours) at 75 °C. The POP_DH can retain the trapped iodine up to seven days without any significant release which makes it a suitable material suitable for storing iodine. The presence of O and N heteroatoms (imine linkages) also enable POP_DH to remove iodine species dissolved in water. Herein, the iodine removal is quite rapid with about 99 % of iodine captured within 2 h. POP_DH samples can be recycled up to five rounds for iodine capture with only small changes in performance as an adsorbent. Overall, POP_DH is promising material for capture of radioactive iodine from various media.

Xe Recovery from Nuclear Power Plants Off-Gas Streams: Molecular Simulations of Gas Permeation through DD3R Zeolite Membrane.

Recent experimental work has shown zeolite membrane-based separation as a promising potential technology for Kr/Xe gas mixtures due to its much lower energy requirements in comparison to cryogenic distillation, the conventional separation method for such mixtures. Such a separation is also economically rewarding because Xe is in high demand, as a valuable product for many applications/processes. In this work, we have used Molecular Dynamics (MD) simulations to study the effects of different conditions, i.e., temperature, pressure, and gas feed composition, on Kr/Xe separation performance via DD3R zeolite membranes. We provide a comprehensive study of the permeation of the different gas species, density profiles, and diffusion coefficients. Molecular simulations show that if the feed is changed from pure Kr/Xe to an equimolar mixture, the Kr/Xe separation factor increases, which agrees with experiments. In addition, when Ar is introduced as a sweep gas, the adsorption of both Kr and Xe increases, while the permeation of pure Kr increases. A similar behavior is observed with equimolar mixtures of Kr/Xe with Ar as the sweep gas. High-separation Kr/Xe selectivity is observed at 50 atm and 425 K but with low total permeation rates. Changing pressure and temperature are found to have profound effects on optimizing the separation selectivity and the permeation throughput.

Influence of Interfering Ions and Adsorption Temperature on Radioactive Iodine Removal Efficiency and Stability of Ni-MOF-74 and Zr-UiO-66.

Metal-organic frameworks (MOFs) often exhibit an exceptional adsorption-based separation performance for a variety of gases, ions, and liquids. While most radioactive iodine removal studies focus on the capture of radioactive iodine from off-gas streams, few studies have systematically investigated the effect of structure-property relationships of MOFs on iodine removal performance in the presence of interfering ions in liquid solutions. Herein, we investigated the iodide ion (I-) adsorption performance of two model MOFs (e.g., Ni-MOF-74 and Zr-UiO-66) in liquid phase as a function of iodine concentration (e.g., 0.125 to 0.25 and 0.50 mmol/L) and adsorption temperature (e.g., 25 to 40 and 60 °C), and in the presence of interfering ions such as Cl- and CO32- through batch-mode experiments. Under identical experimental conditions, Ni-MOF-74 outperformed Zr-UiO-66 in immobilizing iodine from the solution by achieving a maximum iodine removal efficiency of 97% at 60 °C. The results showed that the presence of other interfering ions marginally affects the iodine removal efficiency (e.g., capacity and rate of iodine capture) over both MOF adsorbents. The adsorption kinetics was found to be controlled by multiple transport processes encompassing external surface adsorption, intraparticle diffusion, and final equilibrium. Moreover, the leach test results revealed 8 and 12% iodine release from Ni-MOF-74 and Zr-UiO-66, respectively, at 25 °C after 48 h aging. This study establishes guiding principles for sustainable removal of iodine in the presence of Cl- and CO32- species in cyclohexane.

Removal of gaseous methyl iodide using hexamethylenetetramine and triethylenediamine impregnated activated carbon: A comparative study

Radioactive iodine may be released into off-gas streams during both, the normal operation and severe accident of nuclear power plant in both organic and inorganic forms. Methyl iodide formation results from the reaction between radioactive iodine and organic products (like paint and cable coatings) present within the containment. For the removal of methyl iodide (MeI) gas, activated carbon (AC) was impregnated with 2, 5, 8 and 10 wt% of hexamethylenetetramine (HMTA) and triethylenediamine (TEDA). Characterization of the raw and impregnated activated carbon (IAC) was done by XRD, SEM, Raman, BET and TGA. Removal efficiency of MeI was evaluated using breakthrough experiments by varying weight percent of TEDA and HMTA. Both TEDA and HMTA-rich AC exhibited significant MeI adsorption capacity. TEDA-IAC was more effective for the elimination of MeI which adsorbed maximum 473 mg/g at low temperatures, whereas HMTA-IAC with high porosity had a comparatively high adsorption capacity at high temperatures due to its stability as compared to TEDA-IAC and adsorbed maximum 245 mg/g MeI. When raw AC was compared to IACs, results demonstrated that adsorption capacity of MeI improved up to 64 % for TEDA and 54 % for HMTA impregnated ACs.Langmuir model was well fitted to adsorption equilibrium data, and second-order model explained adsorption kinetics. Thermodynamic parameters study confirmed that the reaction is exothermic and spontaneous in nature.

Chemically Stable and Heteroatom Containing Porous Organic Polymers for Efficient Iodine Vapor Capture and its Storage

The uses of nuclear reactions are gaining importance in energy and medical therapy applications. Production and safe management of radioactive waste is a major operational challenge. Proper treatment and storage of nuclear waste are important while considering nuclear energy for various applications. While reprocessing used nuclear fuel (UNF), handling of volatile radioactive wastes (e.g., radioisotopes of iodine: 129I/131I) requires special attention. Iodine is present in off-gas streams as either molecular iodine (I2) or organic iodides. 129I is less radioactive than 131I, but has an extremely long half-life. Both are highly toxic, and their nearly quantitative retention from off-gas streams requires packing of iodine filters with efficient adsorbents. Thus, there is a need to develop materials with efficient iodine vapor capture/storage capabilities. Herein, a set of four porous organic polymers are presented that are rich in heteroatoms and possess abundant π-arene motifs with which p-orbitals on iodine can interact effectively via charge-transfer complexations. To mimic the conditions of a UNF reprocessing facility, gas-phase iodine capture experiments were performed under various conditions (dry/humid conditions and at 75 °C/25 °C). The maximum iodine uptake capacity of one of the materials (HPOP-4: 6.25 g/g at 75 °C and 4.35 g/g at 25 °C) is higher than several other iodine vapor adsorbents reported to date. The retention of trapped iodine by HPOPs at 25 °C is also quite remarkable with only 2–3% weight loss from iodine-loaded HPOPs, which makes HPOPs potential material for the storage/transportation of captured radioiodine. The results confirm desirable properties in HPOPs such as facile synthesis, high physiochemical stabilities, good moisture tolerance, rapid adsorption kinetics, and efficient reusability with low compromise in capture performance upon regeneration. These benefits render HPOPs as strong contenders for packing filters used for retaining radioiodine during cleaning either off-gas streams or annulus exhaust air (during “loss of coolant accident”).

Boosting Xe/Kr separation by a Mixed-linker strategy in Radiation-Resistant Aluminum-Based Metal − Organic frameworks

Capturing and separating radioactive isotopes of Xenon (Xe) and Krypton (Kr) from off-gas streams in the reprocessing of used nuclear fuel (UNF) gaseous radioactive nuclides emerges as a major concern to meet the rapid growth and sustainable development of nuclear energy. Owing to the inert atomic gases (Xe and Kr) nature without dipole or quadruple moments and their existing extremely low concentrations in radioactive off-gas mixture, it is a grand challenge to design radiation-resistant porous adsorbents for efficient Xe capture and Xe/Kr separation at dilute conditions. Herein, we report a mixed-linker strategy to realize a confined aliphatic pore environment in high radioactive stable CAU-10 type Aluminum-based MOFs using isophthalate and 5-methylisophthalate as mixed linkers for Xe/Kr separation at low concentration. By systematically tune the ratio of the two linkers, the precise and appropriate amount of aliphatic methyl groups could be immobilized on the framework to achieve delicate regulation of pore structure (pore shape and pore size), which significantly increase Xe binding affinity. Mixed-linker CAU-10-H-CH3-0.21–0.79 shows significantly enhanced Xe capture and separation performance at dilute conditions compared to pristine CAU-10-H and fully methyl functionalized CAU-10-CH3, demonstrated by adsorption isotherms and breakthrough curves. The high radioactive stability of CAU-10 type Al-MOFs was also identified by gamma-ray irradiation experiments, suggesting a great potential for practical application.

Lead-vanadate sorbents for iodine trapping and their conversion into an iodoapatite-based conditioning matrix.

New lead-vanadate based sorbents were synthesized with the aim to entrap and confine gaseous iodine in off-gas streams coming from reprocessing facilities of spent nuclear fuel. Their synthesis relies on the shaping of a lead-vanadate, lead sulfide and alginic acid mix as millimetric beads. These beads were calcined between 220°C and 500°C to remove organic alginic compounds template. However, according to the calcination temperature, lead sulfide could be partially oxidized, limiting iodine loading capacity. A compromise temperature between 290°C and 350°C was found to remove most of the alginic acid template and avoiding lead sulfide oxidation. These sorbents were tested for iodine trapping in static conditions at 60°C. They performed well with a sorption capacity up to 155mg.g-1 by forming PbI2. Furthermore, these iodine-loaded sorbents could be easily converted into an iodine-containing lead-vanadate apatite matrix by spark plasma sintering. A dense sample was produced for a sintering temperature of 500°C under 70MPa. Such a material could be suitable for radioactive iodine conditioning in deep geological disposal. Finally, lead-vanadate sorbents could provide an easy way to entrap and confine radioactive iodine from off-gas streams into a durable material within a few steps.

Process Design and Techno-Economic Assessment of biogenic CO2 Hydrogenation-to-Methanol with innovative catalyst

A small-scale 10 ton per day methanol (MeOH) synthesis plant, from CO2 and hydrogen, is designed and simulated with Aspen Plus and a techno-economic analysis is conducted. The e-fuel (MeOH) is produced in a conventional fixed bed reactor featuring an innovative Cu/Zn/Al/Zr catalyst, converting biogenic CO2 from a biogas upgrading plant with H2 produced by a grid powered PEM electrolyzer. The process is thermally autonomous as a result of heat integration and combustion of purged unconverted reactants. A sensitivity analysis is carried out in order to evaluate and compare the impact of the different technical (purge fraction, Gas Hourly Space Velocity and Pressure of the methanol synthesis) and economic parameters (Capital Charge Factor, electricity and H2 cost) on the Levelized Cost Of Methanol (LCOM). Results show that, although the energy efficiency is greater (47.4 % electricity to methanol conversion) in the scenario with “self-sufficiency” in which all the net heat required by the process is provided by off-gas streams, the case with the highest profitability is the one with maximum methanol yield and, therefore, minimum purge and non-zero thermal energy import (provided by a biogas boiler). The best case scenario features a LCOM equal to 1,361 €/tonMeOH, with a GHSV of 7,500 h−1 and synthesis reactor operating at 70 bar, 250 °C. H2 production cost is the key variable and shall be reduced from the base case value of 5.8 €/kgH2 to 1.6 €/kgH2 in order to make the CO2 to methanol plant competitive with a MeOH market price of 550 €/tonMeOH; synthesis reactor operating conditions have more limited impact from a cost perspective, except for the purge fraction that shall be optimized to maximize the amount of MeOH produced.

A CO2 valorization plant to produce light hydrocarbons: Kinetic model, process design and life cycle assessment

Reliable Life Cycle Assessment (LCA) of processes for valorization of CO2-rich off-gas streams requires multidisciplinary contributions that span the development of active and selective catalysts, reactor design, plant modeling and optimization, as well as environmental impact analysis. Herein, we present the design and study of a CO2 valorization plant through methanol-mediated (tandem) hydrogenation to light hydrocarbons, with propane as the most abundant product. A state-of-the-art PdZn/ZrO2 + SAPO-34 catalyst combination was screened for catalytic activity and selectivity in a wide operation range. Optimal process conditions were found at 350 °C, 30–40 bar and co-feeding of CO2/CO. Kinetic parameters for the tandem reaction were extracted and used for the design of a multi-layer reactor, where the two catalysts are distributed according to: (i) CO2-to-methanol catalyst; (ii) mixed catalyst bed, and; (iii) methanol-to-hydrocarbons catalyst. This configuration outperformed the conventional dual bed and mixed bed reactor configurations in terms of process design. A Life Cycle Assessment of the plant suggested that a substantial decrease in the global warming impact of propane production will be highly driven by using green hydrogen from either solar or wind sources, although the comparison with fossil-derived propane indicated already a reasonable improvement even when using grey hydrogen from natural gas.

An activated carbon from walnut shell for dynamic capture of high concentration gaseous iodine

In order to capture the high concentration gaseous iodine from off-gas streams under nuclear accident conditions, an advanced activated carbon was prepared by using walnut shell as a raw material and zinc chloride as an activator agent (named WS-ZnCl2). The pore structure and functional groups characteristics of the adsorbent were researched via three techniques including N2 adsorption–desorption isotherms, transmission electron microscope (TEM), and Fourier transform infrared spectroscopy (FTIR). The Brunauer-Emmett-Teller (BET) surface area, the total pore volume and the average pore size of the adsorbent were observed to be 1360 m2/g, 0.68 cm3/g and 2.00 nm, respectively. In addition, the adsorption capacities of the adsorbent to capture gaseous iodine were investigated with static and dynamic experimental adsorption methods. The results of the static experimental adsorption indicated that the gaseous iodine equilibrium adsorption capacity of the walnut shell before and after ZnCl2 activation increased from 606 mg/g to 2374 mg/g at condition of 80 °C and ambient pressure. The dynamic adsorption performance of the adsorbent for capture of gaseous iodine was studied by varying operating parameters, such as temperature, adsorption column height, and the flow rate. More significantly, the maximum dynamic adsorption capacity of the adsorbent for capture gaseous iodine reached a record of 1634 mg/g at 60 °C, 2.2 cm and 250 mL/min. Finally, the importance ranking of the influencing factors on the dynamic adsorption was analyzed by Grey relational analysis (GRA) method. The results showed that adsorption capacity was obviously affected by flow rate, whereas adsorption time was highly influenced by adsorption column height. The adsorbent researched in this paper has potential to capture high concentration gaseous iodine.

Catalytic Effects of Silver in Iodine Reactors for Dissolved Used Nuclear Fuel

The dissolution of used nuclear fuel generates a variety of off-gasses including flammable hydrogen and other species that are a concern for environmental release. The H-Canyon facility at the Savannah River Site is currently dissolving aluminum-clad research reactor fuel from material test reactors and the High Flux Isotope Reactor (HFIR) using a mercury-catalyzed nitric acid flowsheet. Savannah River National Laboratory recently developed and deployed a Raman spectrometer to monitor the off-gas stream from the dissolution process. Results from these measurements indicated a lack of the expected hydrogen, nitrous oxide, and nitric oxide in the off-gas stream. It was proposed that the silver on the silver nitrate–coated berl saddles present in the reactors for iodine capture were acting as a catalytic hydrogen recombiner. Nitric oxide is readily oxidized to nitrogen dioxide under normal conditions, but it was unclear what happened to the nitrous oxide. A laboratory-scale iodine reactor was assembled and filled with silver nitrate–coated berl saddles to help ascertain the fate of nitrous oxide and hydrogen. Testing with this laboratory-scale reactor observed the recombination of hydrogen when a simulated dissolver off-gas was passed through the reactor containing silver nitrate–coated berl saddles at the approximate temperatures seen in H-Canyon. However, the nitrous oxide concentration was unchanged, suggesting a more complex process occurring within the off-gas stream before it reaches the iodine reactors at H-Canyon.

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Selective and simultaneous membrane separation of CO and H2 from N2 by protic chlorocuprate ionic liquids

Efficient recovery of CO and H2 from offgas streams is environmentally and economically meaningful from the view point of the wide use of syngas (CO/H2) in the chemical industry. This work reports selective and simultaneous separation of CO and H2 from N2 using protic chlorocuprate ionic liquids (PCILs)-based membranes. The chemical structures of the prepared PCILs were characterized using FTIR, NMR and ESI-MS, and the thermal stability, melting points, viscosity and density of PCILs were determined. The morphology and elemental distribution of PCIL-based membranes were characterized by SEM and EDS. Facilitated transport of CO is observed in these membranes, and the CO permeability is up to 178.3 barrers (0.1 bar, 40 °C) in [TEAH][CuCl2], with a CO/N2 selectivity of 26.2. H2 permeability and H2/N2 selectivity are also found to reach 198.2 barrers (0.5 bar, 40 °C) and 29.1, respectively. The permeability of CO and the selectivity of CO/N2 can be further optimized to 405.9 barrers and 69.9 by altering the Cu(I) content, respectively. In addition, the selectivity of CO/H2 can be tuned drastically via varying the Cu(I) content (from 0.77 to 12.0) and the operating temperature (from 2.14 to 0.42), which may be applied to the composition adjustment of syngas. In a word, this work offers a new strategy for designing IL-based membranes that used for CO and H2 capture.

Efficient and simultaneous capture of iodine and methyl iodide achieved by a covalent organic framework

Radioactive molecular iodine (I2) and organic iodides, mainly methyl iodide (CH3I), coexist in the off-gas stream of nuclear power plants at low concentrations, whereas few adsorbents can effectively adsorb low-concentration I2 and CH3I simultaneously. Here we demonstrate that the I2 adsorption can occur on various adsorptive sites and be promoted through intermolecular interactions. The CH3I adsorption capacity is positively correlated with the content of strong binding sites but is unrelated to the textural properties of the adsorbent. These insights allow us to design a covalent organic framework to simultaneously capture I2 and CH3I at low concentrations. The developed material, COF-TAPT, combines high crystallinity, a large surface area, and abundant nucleophilic groups and exhibits a record-high static CH3I adsorption capacity (1.53 g·g−1 at 25 °C). In the dynamic mixed-gas adsorption with 150 ppm of I2 and 50 ppm of CH3I, COF-TAPT presents an excellent total iodine capture capacity (1.51 g·g−1), surpassing various benchmark adsorbents. This work deepens the understanding of I2/CH3I adsorption mechanisms, providing guidance for the development of novel adsorbents for related applications.

Monitoring Noble Gases (Xe and Kr) and Aerosols (Cs and Rb) in a Molten Salt Reactor Surrogate Off-Gas Stream Using Laser-Induced Breakdown Spectroscopy (LIBS).

This study with surrogate materials shows that laser-induced breakdown spectroscopy (LIBS) is a robust tool with promising capability toward monitoring gaseous (Xe and Kr) and aerosol (Cs and Rb) species in an off-gas stream from a molten salt reactor (MSR). MSRs will continually evolve fission products into the cover gas flowing across the reactor headspace. The cover gas entrains Xe and Kr gases, along with aerosol particles, before passing into an off-gas treatment system. Univariate models of Xe and Kr peaks showed a strong correlation to concentration indicated by their coefficients of determination of 0.983 and 0.997, respectively. Multivariate models were built for all four analytes using partial least squares regression coupled with preprocessing steps including normalization, trimming, and/or genetic algorithm derived filters. The models were evaluated by predicting the concentrations of the analytes in four validation samples, in which all calibration models were successfully validated at a confidence interval of 99.9%. Lastly, pressure controllers were used to regulate the mass flow rate of Kr flowing into the measurement cell in sinusoidal and stepwise waveforms to test the real-time monitoring capabilities of the regression models. Both univariate and partial least squares Kr models were able to successfully quantify the gas concentration in the real-time evaluation. The root mean squared error of prediction (RMSEP) values for these real-time tests were calculated to be 0.051, 0.060, and 0.121 mol% demonstrating the measurement systems' capability to perform online monitoring with acceptable accuracy.