A Chemical Perspective on the Tellurium Source Term in the Context of Severe Nuclear Power Plant Accidents

In the event of a severe nuclear accident, one of the biggest concerns is the release of radioactive nuclides.Typically, the most volatile is likely to be released. One that is considered among the most volatile istellurium. Additionally, health implications towards the public by tellurium can be by itself or the decayproduct iodine.Several aspects concerning the volatility under mainly oxidizing (e.g., air ingress) and inert (injectionof inert gas preventing hydrogen explosion) conditions of the tellurium source term from a chemicalperspective have been explored. These aspects are the consequence of seawater as an emergency coolingmedium, the effect of cesium iodide on the transport on and interaction in the reactor coolant system(RCS), and the effect of surfaces located inside a boiling water reactor (BWR). Finally, the effectivenessof the containment spray system (CSS) using different solutions was investigated.Under oxidizing conditions, tellurium was noticeably affected by all aspects. The seawater experimentsshowed that tellurium was enhanced by sodium chloride. From the RCS experiments, the addition ofcesium iodide decreased the transported amount of tellurium and a new tellurium species was observed,but uncertain if it was correlated to cesium. Regarding the BWR surfaces, only zinc was removed fromthe surface by the tellurium when humidity was high. However, neither if this enhanced the volatility orif a new compound formed were clear. Finally, high removal efficiency was observed of the spray systemunder all conditions.The investigation of tellurium under inert conditions had less of the investigated aspect affecting thevolatility. The seawater experiment showed no change to the volatilization of tellurium. However, in theRCS the addition of cesium iodide resulted in both an increase in transported tellurium and new telluriumspecies, potentially correlated to cesium. None of the BWR surfaces had any effect on tellurium. Finally,the effectiveness of the CSS was lower than under oxidizing conditions but still above 50%. However,the addition of cesium iodide considerably enhanced the removal. Therefore, indicating a change of thetellurium speciation.From this work, it is clear that the chemistry concerning the volatility of tellurium still needs furtherattention. Under an air ingress scenario, using seawater would enhance the release of tellurium. Opposedto the cesium iodide, that would reduce it. In the containment, tellurium would interact with surfacesmade out of zinc. For a scenario when inert gas has been injected, the use of seawater would have lessimpact if any and the presence of cesium iodide would enhance the transport of tellurium. No surfacein the BWR containment would interfere. However, under both scenarios, an intact containment and afunctional CSS would effectively trap the tellurium in the sump

Potential tellurium deposits in the BWR containment during a severe nuclear accident

The release of fission products to the environment is one of the concerns with nuclear power. During an accident, the most likely released are the volatile fission products i.e., tellurium. To evaluate the behavior of tellurium in the event of an accident, it was heated under different conditions (oxidizing, inert, reducing; both dry and humidified). The formed vapor was transported to surfaces (aluminum, copper, zinc) at room temperature that can be found in the BWR-containment. All formed deposits were examined for morphology and species. Moreover, the content of sodium hydroxide liquid traps following the metal surfaces and filter was also investigated. In these traps, the highest amount of tellurium was found under humid-reducing followed by humid-oxidizing conditions. In the deposit removed from the zinc surface acquired under the latter conditions, elemental analysis observed zinc, indicating a possible reaction between tellurium and zinc. The corresponding trap showed significant amounts of zinc. (C) 2020 The Author(s). Published by Elsevier Ltd

Tellurium interaction with surfaces in the containment and sea-salt residue

In the event of a nuclear accident, the release of radionuclides is always a concern. The\ua0extent of such releases is affected by several factors, for example type of atmosphere, temperature, and what structural materials are present during the accident. The release\ua0of tellurium is especially worrying due its volatility, reactivity, and decay product of iodine. Moreover, the radiological and chemical toxicity of tellurium will during an\ua0accident be considerably problematic, to the public and nature.\ua0This work is divided into two experimental parts in order to determine: (1) the interaction between tellurium and metallic structural material found in the containment and (2) investigate the potential effect when using seawater as a coolant focusing on sea-salt residue. All experiments were performed at the relevant temperature (depending on the which part) under oxidizing and inert conditions and for the containment experiments humidity was also investigated. The structural material investigated were the metal surfaces aluminum, zinc, and copper with the aim of determining morphology, chemical speciation and if a reaction occurred between the metal surface and tellurium. For the investigation of seawater, determining if a chemical reaction(s) between tellurium and sodium chloride occurs and at what temperature. Results from the containment experiments using a furnace showed signs of possible reaction between tellurium and the copper surface under inert humid conditions close to room temperature. Otherwise, tellurium deposition occurred on the metal surfaces with no observable chemical reaction and no strong attachment to the surface. The deposit formed on the surfaces and the observed chemical species under the different conditions, determined using different spectroscopy methods, were as follows: TeO2 under oxidizing with (crystal structure paratellurite) and without humidity (crystal structures: paratellurite and orthorhombic), Te-metallic under inert conditions both with and without humidity, and finally Cu7Te4 was seen in the deposits on the copper surface under humid inert conditions. For the seawater investigation, two methods where used thermogravimetric analysis and furnace experiments. The results from these methods showed that under inert conditions, no indication of interaction was seen. However, for oxidizing conditions an interaction for all samples was observed that prevented an otherwise seen mass increase of the tellurium reference. Through the furnace experiments, the appearance of the samples at increasing temperatures were studied and used to support the thermogravimetric analysis

Chemical interaction between sea-salt and tellurium, between 300 and 1180 K

As an emergency action during the Fukushima accident, seawater was used to maintain cooling. To evaluate the effect of the salt on fission-products, sodium chloride, and tellurium were heated together using different ratios in different atmospheres (inert or oxidizing) using thermogravimetric analysis. The experiment under inert conditions showed no indication of interaction. However, under oxidizing conditions an interaction for all samples was observed that prevented an otherwise observed mass increase of the tellurium reference. The change in the appearance of the samples at increasing temperatures was studied by heating them in a furnace

Tellurium retention by containment spray system

A containment spray system is used to mitigate the source term from the containment building to the environment as part of the severe accident management actions. Tellurium is one of the volatile fission products and many of the tellurium isotopes decay into iodine, which causes a threat to the public due to its radiotoxicity and build-up in the thyroid gland. The removal efficiency of the containment spray system model against tellurium species formed under severe accident conditions was investigated with experiments and MELCOR simulations. The results indicated efficient removal of tellurium aerosols in the air atmosphere, whereas a decrease in the efficiency was observed in the nitrogen atmosphere. Gaseous tellurium species were not formed in significant amounts during the experiments and therefore, the removal efficiency due to different spray chemistry conditions could not be accurately analysed. However, the alkaline chemicals used in the spray solution seemed to form airborne particles, increasing the overall aerosol transport in the process independently of CsI or Te aerosol transport

Leaching and recovery of rare-earth elements from neodymium magnet waste using organic acids

Over the last decade, rare-earth elements (REEs) have become critical in the European Union (EU) in terms of supply risk, and they remain critical to this day. End-of-life electronic scrap (e-scrap) recycling can provide a partial solution to the supply of REEs in the EU. One such product is end-of-life neodymium (NdFeB) magnets, which can be a feasible source of Nd, Dy, and Pr. REEs are normally leached out of NdFeB magnet waste using strong mineral acids, which can have an adverse impact on the environment in case of accidental release. Organic acids can be a solution to this problem due to easier handling, degradability, and less poisonous gas evolution during leaching. However, the literature on leaching NdFeB magnets waste with organic acids is very scarce and poorly investigated. This paper investigates the recovery of Nd, Pr, and Dy from NdFeB magnets waste powder using leaching and solvent extraction. The goal was to determine potential selectivity between the recovery of REEs and other impurities in the material. Citric acid and acetic acid were used as leaching agents, while di-(2-ethylhexyl) phosphoric acid (D2EHPA) was used for preliminary solvent extraction tests. The highest leaching efficiencies were achieved with 1 mol/L citric acid (where almost 100% of the REEs were leached after 24 h) and 1 mol/L acetic acid (where >95% of the REEs were leached). Fe and Co—two major impurities—were co-leached into the solution, and no leaching selectivity was achieved between the impurities and the REEs. The solvent extraction experiments with D2EHPA in Solvent 70 on 1 mol/L leachates of both acetic acid and citric acid showed much higher affinity for Nd than Fe, with better extraction properties observed in acetic acid leachate. The results showed that acetic acid and citric acid are feasible for the recovery of REEs out of NdFeB waste under certain conditions

Tellurium determination by three modes of instrumental neutron activation analysis in aerosol filters and trap solutions for the simulation of a severe nuclear accident

Tellurium belongs to the elements not frequently determined by neutron activation analysis (NAA) or other analytical methods. We present results of a new methodological study using three independent modes of instrumental NAA (INAA) using the\ua0123mTe,\ua0131Te and\ua0131I radionuclides. We compare the results obtained in terms of accuracy, precision and limits of detection (LOD). We utilized the INAA procedures tested for the tellurium determination in aerosol filters and trap solutions in a model experiment aimed at reducing the knowledge gap concerning the behaviour of\ua0132Te, a radiologically significant fission product, which constitutes a considerable health risk towards the public in case of its release in a severe nuclear power plant accident. We found that the nuclear reaction\ua0130Te(n,γ)131Te and gamma-ray spectrometric measurement of\ua0131I, a descendant of\ua0131Te, is the most sensitive way of Te determination by INAA providing as low LOD values as 0.15\ua0\ub5g of Te in the Teflon aerosol filters and 0.22\ua0\ub5g mL-1\ua0in the 0.1\ua0M NaOH trap solutions. The three independent INAA modes allowed employing the self-verification principle of INAA for increasing the trustworthiness of our results. Finally, we also point to the indispensable role of the non-destructive feature of INAA for assay of samples, such as Teflon aerosol filters, that are difficult to be analysed by other analytical methods requiring complete sample destruction without analyte losses

Tellurium transport in the RCS under conditions relevant for severe nuclear accidents

In the case of a severe nuclear power plant accident, tellurium is one of the more problematic and volatile fission products. If released it could become a health issue as it decays to iodine which accumulates in the thyroid gland. Research exists, that indicates tellurium likely interacts with caesium under severe accident conditions, thus it is important to further explore related phenomenon. In this work, tellurium was exposed to high temperature under oxidizing and inert conditions simulating severe accident conditions with and without airborne caesium iodide to determine the effect on the tellurium source term. The effect of caesium iodide was noticeable on tellurium transport behaviour in the gas phase under oxidizing and inert conditions. Under humid oxidizing conditions with caesium iodide, no significant impact on the total aerosol mass transport was noticed. However, less tellurium was transported through the model primary circuit and a potentially new compound was observed on the filter located after this model. Comparing inert dry to humid with caesium iodide showed an increase in the total aerosol mass transport whereas there was a decrease noticed of the tellurium reaching the filter after the model primary circuit. In the latter case, new unidentified compound(s) correlated to caesium, iodine and tellurium were observed on the filter located after the model. In this work, evidence was found that tellurium behaviour will be affected by caesium iodide under the investigated conditions. Moreover, it seems that under inert conditions the formed compounds may be stable at close to ambient temperatures. Unlike under oxidizing conditions, where dissociation likely occurred