| 1. |
- Börjesson Sandén, Fredrik, 1995, et al.
(författare)
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Effects of boric acid on volatile tellurium in severe accident conditions
- 2024
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Ingår i: Annals of Nuclear Energy. - 0306-4549 .- 1873-2100. ; 200
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Tidskriftsartikel (refereegranskat)abstract
- Boric acid is used in light-water nuclear reactors to control the reactor and is expected to be present as part of the chemistry of a severe accident. Therefore, its influence on other prominent species expected in an accident must be investigated. One such species is tellurium. In the present study, tellurium is volatized, and boric acid is dissolved and injected into the system as a means of studying the interaction between it and tellurium. The experiments were evaluated with ICP-MS and XPS. Results suggest that while there is no direct interaction, boric acid still affects the tendency for tellurium to oxidize. In general, less oxidation was detected in the presence of boric acid than in its absence, especially at high temperatures. The species formed upon oxidation was determined to be TeO2. Since tellurium metal is more volatile than TeO2, this may have implication in a wider severe accident context.
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| 2. |
- Espegren, Fredrik, 1989, et al.
(författare)
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Tellurium transport in the RCS under conditions relevant for severe nuclear accidents
- 2021
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Ingår i: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 139
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Karkela, T., et al.
(författare)
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Tellurium retention by containment spray system
- 2021
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 164
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Kučera, Jan, et al.
(författare)
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Tellurium determination by three modes of instrumental neutron activation analysis in aerosol filters and trap solutions for the simulation of a severe nuclear accident
- 2020
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Ingår i: Microchemical Journal. - : Elsevier BV. - 0026-265X. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- 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 123mTe, 131Te and 131I 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 132Te, 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 130Te(n,γ)131Te and gamma-ray spectrometric measurement of 131I, a descendant of 131Te, is the most sensitive way of Te determination by INAA providing as low LOD values as 0.15 µg of Te in the Teflon aerosol filters and 0.22 µg mL-1 in the 0.1 M 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.
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| 5. |
- Pasi, Anna-Elina, 1993, et al.
(författare)
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Gas phase interactions between tellurium and organic material in severe nuclear accident scenarios
- 2024
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Ingår i: Annals of Nuclear Energy. - 0306-4549 .- 1873-2100. ; 197
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Tidskriftsartikel (refereegranskat)abstract
- One of the volatile fission products potentially released during a severe nuclear accident is tellurium. Recently, tellurium has been shown to form volatile organic tellurides from paint solvents in aqueous solutions which could further increase the release. However, not much is known about the possible interactions between tellurium and organic material in gas phase. In this study, tellurium was exposed to conditions simulating the containment atmosphere during an accident. Moreover, volatile organic compounds were introduced to the gas phase representing the presence of organic material in the containment during the accident. The results suggest that tellurium aerosols and organic material interact in the gas phase which was observed as an increase in the gaseous fraction and a change in the XPS spectra. Although no exact species were identified, the results raise questions about the behavior of tellurium in severe accident conditions, especially, regarding the reactions involving organic material.
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| 6. |
- Pasi, Anna-Elina, 1993
(författare)
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Mobilization and Management of Tellurium in Severe Accident Scenarios
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Safety is one of the highest priorities in any industry. In the nuclear industry, safety is in the essence since in case of a nuclear accident, the consequences can be long-lasting, hazardous, and devastating to the public, environment, and the industry. Although only two accidents of highest significance have occurred, their influence is still present today. One of the most severe consequences of a severe nuclear reactor accident is the release of radioactive material to the environment. Different characteristics, such as volatility, toxicity, and half-life, of the released elements determine their effect and significance. Among the released radionuclides is tellurium. The tellurium isotopes released in the major accidents are highly volatile and have half-lives long enough to make tellurium important especially in the early stages of an accident. The released tellurium isotopes can cause increased radiation dose to the public during the first weeks after the accident. Moreover, many of the tellurium isotopes released decay to iodine isotopes which is also a concern due to the increased risk of thyroid cancer iodine can cause. The aim of this work was to investigate phenomena involving tellurium occurring inside the containment building during a severe nuclear accident. The work is divided into mobilization of tellurium species and their management. The results obtained in this research provide valuable information on the behavior of tellurium in severe accident scenarios. The reactions leading to increased solubility and volatility were shown. High emphasis was put on the formation, stability, and mitigation of organic tellurides. The formation of a variety of organic tellurides from paint solvents under gamma irradiation was observed. This causes concerns about possible re-volatilization leading to post-accident releases. In addition to the increased mobility, this work provides information on the mitigation of tellurium species in accident scenarios. The containment spray system was found to be relatively effective in removing tellurium species from the containment atmosphere. In addition, activated charcoal materials trapped dimethyl telluride well. However, some reversibility was observed which raises interest on the adsorption mechanism. The results presented in this work lay the foundation for further studies on tellurium behavior in the containment. The evidence showing the formation of organic tellurides is especially significant since that could potentially lead to increased releases.
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| 7. |
- Pasi, Anna-Elina, 1993, et al.
(författare)
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Organic Telluride Formation from Paint Solvents Under Gamma Irradiation
- 2022
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 208:11, s. 1734-1744
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between tellurium and organic material during a nuclear reactor accident are critical to source term estimations because of the possible formation of volatile species. Reactions taking place in the containment sump are of interest since these can lead to re-volatilization and increase the fission product source term. This paper presents results from experiments investigating the interaction of tellurium dioxide with three paint solvents-texanol ester, methyl isobutyl ketone, and toluene-under containment sump conditions. The experiments were performed by irradiating a mixed solution of tellurium dioxide and paint solvents at a dose rate of 4 kGy/h up to 300 kGy. The resulting samples were analyzed for tellurium concentration and speciation. Tellurium(IV) was found to reduce to metallic tellurium under irradiation when paint solvents were present. More importantly, several volatile organic tellurides were identified in the irradiated samples, which suggests that tellurium can form volatile species in sump conditions when in contact with dissolved paint solvents. This paper provides novel evidence of organic telluride formation in the sump and raises further interest in tellurium chemistry during a severe nuclear reactor accident.
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| 8. |
- Pasi, Anna-Elina, 1993, et al.
(författare)
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Radiolytic degradation of dimethyl telluride in aqueous solutions
- 2023
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 1879-0895 .- 0969-806X. ; 207
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Tidskriftsartikel (refereegranskat)abstract
- The formation of volatile radioactive species is a major concern in severe nuclear reactor accident scenarios. Release of radioactive material to the environment is highly governed by the volatility of the species and therefore it its crucial to understand the behavior of any such species during the accident and the days and weeks following. One of the volatile, yet highly understudied fission products is tellurium. Although tellurium has been released in significant amounts during the major nuclear accidents that have occurred, the knowledge of the behavior is still lacking. Here we present results on the radiolysis of dimethyl telluride, a highly volatile species shown to form in accident conditions. The behavior of dimethyl telluride was investigated under gamma irradiation in various aqueous solutions and conditions representative to severe nuclear reactor accident conditions. The results suggest that dimethyl telluride is relatively stable towards gamma irradiation and its degradation is highly affected by the amount of dissolved oxygen and competing species. It was found that dimethyl telluride degrades via oxidative processes by reacting with oxidizing radiolysis products e.g. •OH, O.-. In the absence of oxygen, several volatile telluride dimers were observed. The results presented here increase the interest in organic tellurides in severe accident conditions and highlight the need for further investigation of the re-volatilization and mitigation of volatile tellurium species.
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| 9. |
- Pasi, Anna-Elina, 1993
(författare)
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Tellurium Behavior and Management in the Liquid Phases in the Containment During a Severe Nuclear Reactor Accident
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- No industry is immune to accidents; however, the consequences and the probability are the parameters to consider when assessing the risks. When considering nuclear power, two of the highest-level accidents have occurred during the course of the commercial use of nuclear energy. The consequences of these events were the release of radioactive material to the environment and increased radiation dose to the people. Severe nuclear accident research is therefore crucial in both minimizing the consequences and assessing the effects of the potential releases. The lessons learned from previous nuclear reactor accidents have resulted in higher safety standards, more accurate source term assessment, and improvements in accident management actions. Yet, there are still uncertainties about the behavior of radionuclides during a severe nuclear reactor accident that need to be addressed. One of the elements released in a severe reactor accident is tellurium. It has several radioactive isotopes that can potentially cause an increased dose in the population if released. Moreover, many of the tellurium isotopes decay to iodine and therefore contribute to the iodine source term. The behavior and release of tellurium have been investigated in the fuel and the reactor system during the past decades. However, the released species, including tellurium, are subjected to different management actions after entering the containment including the containment spray system. The removal efficiency of the spray system towards tellurium species formed under various conditions has been unclear. In this work, the effectiveness was investigated in relation to tellurium species under various atmospheres and in the presence of cesium iodide. In addition, the effect of the chemical composition of the spray was also examined. The spray system was found to be relatively effective in all conditions tested. Moreover, the increase in chemical content of the spray solution increased the removal efficiency. After being removed from the containment atmosphere, the species, including various tellurium compounds, may enter the containment sump. Due to the complex chemistry of tellurium, it is difficult to predict the behavior under different redox conditions and especially under irradiation. This work therefore investigated the behavior of tellurium dioxide was investigated in simplified containment sump conditions in relation to dissolution, redox reactions and interactions with water radiolysis products. The results indicate that radiolysis products have a significant effect on tellurium chemistry in both reducing and oxidizing manner depending on the solution composition. The redox reactions also affect the solubility of tellurium both by increasing and decreasing it depending on the prevailing conditions. The results show that the current information used to assess tellurium source term needs to be re-evaluated for both severe accident management as well as for severe accident code validation purposes.
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| 10. |
- Pasi, Anna-Elina, 1993, et al.
(författare)
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Tellurium Behavior in the Containment Sump: Dissolution, Redox, and Radiolysis Effects
- 2020
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; , s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- In the event of a severe nuclear accident, one major concern is the release of radioactive material into the environment causing potential exposure of the general public to radiation. Among the volatile radionuclides are a range of tellurium isotopes. Due to the radioactivity and the volatility of tellurium, it has to be taken into account when assessing the overall effects of an accident. The interest in tellurium is not limited only to its release but also to the fact that some tellurium isotopes decay to iodine, and thus affect the iodine release behavior. The release and transport behavior of tellurium has been investigated over the past decades, however, the aqueous chemistry of tellurium in the complex containment sump system is still unclear. This study presents the behavior of tellurium dioxide in simplified containment sump conditions in relation to dissolution, redox reactions, and interactions with water radiolysis products. The results indicate that radiolysis products have a significant effect on tellurium chemistry in both a reducing and oxidizing manner depending on the solution composition. The redox reactions also affect the solubility of tellurium. The results show that the current information used to assess tellurium source term needs to be reevaluated for both severe accident management and for code validation purposes.
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