In the event of a nuclear power plant accident, iodine is one of the radionuclides of the greatest issue. Present in various chemical forms, the mitigation of outside releases is a crucial aspect of nuclear safety protection measures during a nuclear accident as these airborne iodine releases pose a significant radiological risk to the exposed population in the short term. Pool scrubbing device is one mean of mitigation. Tests were conducted on to study the scrubbing efficiency in a water pool of volatile iodine species: methyl iodide (CH3I) and molecular iodine (I2). This allows us to determine a Decontamination Factor (DF) for each gaseous species, characterizing its trapping capability. The influence of various physical and chemical factors on the trapping was investigated, the experimental parameters were the gas flow regime, pool’s pH, and pool’s temperature. The retention of CH3I by pool scrubbing was unaffected by the flow regime and pool chemical conditions in contrast to I2. Pool scrubbing appears to be an efficient mean to mitigate I2 releases for bubbly regime and alkaline conditions whereas for CH3I, due to its too high volatility, the retention efficiency remains quite low and cannot be considered as an effective mitigation mean.

Mitigation of gaseous RuO4 is an important issue in nuclear safety in order to reduce potential radiological consequences, either in the context of severe accident arising on pressurized water reactors (oxidizing conditions) or in reprocessing plants (loss of cooling of fission product storage tanks). For the first time, RuO4 trapping was compared using three kinds of materials acting as solid traps: a functionalized MOF UiO-66-NH2, an aminemodified silica and a commercial cerium dioxide. Different experimental conditions of temperature, humidity and gas composition were investigated in order to mimic those prevailing under accident conditions at filtered containment venting system (FCVS) level or in ventilation ducts (gas mixture). At 50 C, the efficiency of UiO-66NH2 for RuO4 trapping was both very high in dry gas and in presence of steam with decontamination factor (DF) in the range 104-105. Under more severe conditions, the retention performances slightly decrease, especially when NO2 was present in the feed gas due to some poisoning of adsorption sites. In presence of amino-modified silica, breakthrough of RuO4(g) occurred at an earlier stage due to its inferior adsorption capacity but the performances of the trap did not deteriorate in presence of steam and NO2 in gas mixture. Under similar conditions, cerium dioxide showed no retention of RuO4(g).

The potential release of fission products (FPs) to the atmosphere during an hypothetical severe accidents on nuclear facilities is a main issue in nuclear safety. Accurate estimation of these releases is crucial for risk assessment and implementation of appropriate measures. To this end, IRSN studies the mitigation of FPs transported in a carrier gas injected through a liquid pool. This process, referred to 'pool scrubbing', can occur in various accident situations in Pressurized Water Reactors (PWRs), such as Filtered Containment Venting Systems (FCVS) or with the Steam Generator Tube Rupture (SGTR), as well as in nuclear-powered submarines or in new Small Modular Reactors (SMRs) with pressurized water. Experiments dealing with characterization of bubbles hydrodynamics and trapping of iodine compounds (decontamination factors measurements) are currently conducted. In this objective, a dedicated facility named TYFON (Trapping and hYdrodynamics for FissiON products behaviour in pool scrubbing) at IRSN enables to perform hydrodynamics and iodine retention tests for different carrier gas injection rates (characterized by Weber number). In this context, advanced results have been obtained on hydrodynamics in the injection zone and CsI aerosol retention. In line, a new study focused on the impact of a saline solution on these phenomena and on bubble plume modelling has been launched. In the long term, all the experimental data collected, including hydrodynamics and the decontamination factor (DF), will be used to improve the modelling of pool scrubbing phenomenon in the ASTEC code developed by IRSN.

The objective of this work is to develop a dedicated test bench to study the dynamic noble gas trapping by porous materials, especially by metal-organic framework (MOF), in a nuclear context. The well-known copper-containing HKUST-1 material is used to determine the influence of different parameters such as temperature, concentration, humidity, MOF bed height or diameter, and velocity of the flow rate on noble gases adsorption (Kr, Xe) in breakthrough sorption experiments. Breakthrough time is shown to be directly related to the MOF bed height, shaping, and gas flow velocity. The adsorption capacities depend not only on the concentration of noble gases in the gas flow but also on the flow velocity. Indeed, when the velocity increases from 0.15 to 1 cm s(-1), the adsorption capacity of Xe increases from 3.46 to 5.15 mu mol g(-1) at 25 degrees C and 1 bar, while the breakthrough time decreases from 7.3 to 2.4 min. The temperature and the presence of water vapor have a negative effect on noble gas adsorption in HKUST-1.

Experimental results are reported on the airborne release, under fire conditions, of hazardous materials dissolved in a mixture of organic solvents [tributylphosphate (TBP) and hydrogenated tetrapropylene (HTP)] representative of the nuclear fuel recycling process. Cerium and ruthenium have been considered, respectively, as stable and volatile fission products that eventually could be released as airborne particles during thermal degradation of contaminated and inflammable liquids. Airborne release fractions (ARFs) and their experimental uncertainties have been determined. Considering fire involving contaminated organic solvents, higher ARFs are reported for ruthenium Ru(+III) (0.99 +/- 1.20%) in comparison with cerium [0.22 +/- 0.31% and 0.20 +/- 0.28% for Ce(+III) and Ce(+IV), respectively]. This discrepancy is partially due to the volatility of ruthenium formed under these conditions. Considering configurations involving an aqueous nitric acid phase placed below contaminated solvents, boiling of this phase enhances the release of contaminant materials: 1.78 +/- 1.06% and 1.01 +/- 1.31% for Ce(+III) and Ce(+IV), respectively, and 12.41 +/- 29.45% for Ru(+III). Analysis of the size distribution, morphology, and chemical composition of the released particles and droplets emitted during HTP/TBP bubble collapse are reported, highlighting the contribution of bubble bursting at the solvent surface to airborne release.

Pool scrubbing has shown potential efficiency to reduce the release of fission products, especially in aerosol forms, into the environment. Considering the large test conditions where pool scrubbing might be encountered, there is still a lack of systematic analysis of this phenomenon, especially its dependence on different hydrodynamic regimes. Experimental work was carried out, where hydrodynamic and decontamination factor measurements were performed. Caesium iodide aerosols were injected into the TYFON facility for different flow regimes (0.08 <= We <= 15 600) by varying both injection flowrate Qinj and nozzle size D0, in which their effects were examined. The Weber number (We) has shown to be capable of characterizing the decontamination factor, when comparing this work with data from literature. Moreover, the different flow regimes induced different sensitivities of aerosol removal mechanisms, where a minimum scrubbing is observed in the transition between bubbly and jet regime. The effect of pool submergence was also investigated in case of bubbly and jet regimes, in which the contribution of residence time and inertial impaction to pool scrubbing was shown. (c) 2023 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

The reprocessing of spent nuclear fuel produces high level liquid waste (HLLW). Due to the decay heat, the concentrated nitric solutions containing fission products (FP) are stored in cooled tanks. Actually, the loss-of-cooling accident on these HLLW storage tanks could lead to releases of radioactive materials to the environment, especially ruthenium volatile species. After a general presentation on the physico-chemical behaviour of ruthenium in concentrated nitric acid, this paper successively details the different transfer modes of ruthenium reported in the literature, and the available trapping techniques. Based on this review, research perspectives are presented aiming at updating data concerning ruthenium behaviour in this context.

As part of study of the volatilization ruthenium behaviour in a boiling nitric solution, this paper presents the results of experiments dealing with the influence of different parameters (Ru and HNO3 concentrations, temperature, water addition) and the effect of in-situ inhibitors to mitigate potential releases. The amount of Ru volatilized from a nitric solution heated at 130 °C is about 2% of initial inventory. The addition of a low amount of inhibitors allowed to prevent ruthenium volatilization. Alternative strategies examined to restrict volatilization are the temperature decrease and the “water feed”, this later is more efficient.

A series of Zr-based UiO-n MOF materials (n=66, 67, 68) have been studied for iodine capture. Gaseous iodine adsorption was collected kinetically from a home-made set-up allowing the continuous measurement of iodine content trapped within UiO-n compounds, with organic functionalities (-H, -CH3 , -Cl, -Br, -(OH)2 , -NO2 , -NH2 , (-NH2 )2 , -CH2 NH2 ) by in-situ UV-Vis spectroscopy. This study emphasizes the role of the amino groups attached to the aromatic rings of the ligands connecting the {Zr6 O4 (OH)4 } brick. In particular, the preferential interaction of iodine with lone-pair groups, such as amino functions, has been experimentally observed and is also based on DFT calculations. Indeed, higher iodine contents were systematically measured for amino-functionalized UiO-66 or UiO-67, compared to the pristine material (up to 1211 mg/g for UiO-67-(NH2 )2 ). However, DFT calculations revealed the highest computed interaction energies for alkylamine groups (-CH2 NH2 ) in UiO-67 (-128.5 kJ/mol for the octahedral cavity), and pointed out the influence of this specific functionality compared with that of an aromatic amine. The encapsulation of iodine within the pore system of UiO-n materials and their amino-derivatives has been analyzed by UV-Vis and Raman spectroscopy. We showed that a systematic conversion of molecular iodine (I2 ) species into anionic I- ones, stabilized as I- ⋅⋅⋅I2 or I3 - complexes within the MOF cavities, occurs when I2 @UiO-n samples are left in ambient light.

106Ru is a radioactive isotope usually generated by the nuclear industry within power plant reactors. During a nuclear accident, 106Ru reacts with oxygen, leading to the production of highly volatile ruthenium tetroxide RuO4. The combination of volatility and radioactivity makes 106RuO4, one of the most radiotoxic species and justifies the development of a specific setup for its capture and immobilization. In this study, we report for the first time the capture and immobilization of gaseous RuO4 within a porous metal-organic framework (UiO-66-NH2). We used specific installation for the production of gaseous RuO4 as well as for the quantification of this gas trapped within the filtering medium. We proved that UiO-66-NH2 has remarkable affinity for RuO4 capture, as this MOF exhibited the worldwide highest RuO4 decontamination factor (DF of 5745), hundreds of times higher than the DF values of sorbents daily used by the nuclear industry (zeolites or activated charcoal). The efficiency of UiO-66-NH2 can be explained by its pore diameters well adapted to the capture and immobilization of RuO4 as well as its conversion into stable RuO2 within the pores. This conversion corresponds to the reactivity of RuO4 with the MOF organic sub-network, leading to the oxidation of terephthalate ligands. As proved by powder X-ray diffraction and NMR techniques, these modifications did not decompose the MOF structure.

The use of an extrusion-spheronization process was investigated to prepare robust and highly porous extrudates and granules starting from UiO-66 and UiO-66_NH2 metal-organic framework powders. As-produced materials were applied to the capture of gaseous iodine and the adsorption of xenon and krypton. In this study, biosourced chitosan and hydroxyethyl cellulose (HEC) are used as binders, added in low amounts (less than 5 wt % of the dried solids), as well as a colloidal silica as a co-binder when required. Characterizations of the final shaped materials reveal that most physicochemical properties are retained, except the textural properties, which are impacted by the process and the proportion of binders (BET surface area reduction from 5 to 33%). On the other hand, the mechanical resistance of the shaped materials toward compression is greatly improved by the presence of binders and their respective contents, from 0.5 N for binderless UiO-66 granules to 17 N for UiO-66@HEC granules. UiO-66_NH2-based granules demonstrated consequent iodine capture after 48 h, up to 527 mg/g, in line with the pristine UiO-66_NH2 powder (565 mg/g) and proportionally to the retaining BET surface area (-5% after shaping). Analogously, the shaped materials presented xenon and krypton sorption isotherms correlated to their BET surface area and high predicted xenon/krypton selectivity, from 7.1 to 9.0. Therefore, binder-aided extrusion-spheronization is an adapted method to produce shaped solids with adequate mechanical resistance and retained functional properties.

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.

Bubble-bubble interactions are relevant to industrial applications, for which air is injected at different flowrates from submerged orifice. These interactions provoke aperiodic bubble formation that affects their departure and size distribution, which is revealed through our experimental data. Air is injected and regulated at flow rate between 10(-4) m(3).s (-1) and10 (-3) m(3).s (-1) from a submerged orifice of inner diameter 12 mm, corresponding to a gas Weber number between 0.16 and 16. Image analysis is carried out to track the formation and departing of bubbles, as well as the formation of a globule, which is a large bubble formed after the bubbles coalescence. Upon increasing the flowrate, the different patterns of bubbling observed have been classified according to the variation of the coalescence position. In a conventional method, bubbles volumes are determined by inspecting the departure frequency and assuming single bubbling spherical pattern. Using the same assumptions and method, we find a good agreement with literature models. Owing to the phenomenological description of the flow, the frequency and volume of globules are characterized. A contrast between the conventional and phenomenological approaches is exposed, revealing a weak applicability of conventional models in estimating bubbles sizes at high flow rates. (c) 2021 Elsevier Ltd. All rights reserved.

This work presents laboratory tests on gaseous RuO4 filtration carried out at IRSN in Cadarache. The objective is to determine if gaseous ruthenium tetroxide can be trapped by metallic filter and sand bed filter, both elements being used in filtered containment venting systems implemented on French pressurized water reactors. The results show no ruthenium tetroxide trapping by physical or chemical adsorption but certain retention is observed resulting from its thermal decomposition into solid ruthenium dioxide. A thermodynamic analysis of the system tends to confirm this conclusion. Chemical stability of RuO4(g) has to be considered as it strongly impacts potential filtration and so potential releases.