| 1. |
- Kučera, Jan, et al.
(author)
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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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In: Microchemical Journal. - : Elsevier BV. - 0026-265X. ; 158
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Journal article (peer-reviewed)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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| 2. |
- Pasi, Anna-Elina, 1993
(author)
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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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Licentiate thesis (other academic/artistic)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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| 3. |
- Pasi, Anna-Elina, 1993, et al.
(author)
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Tellurium Behavior in the Containment Sump: Dissolution, Redox, and Radiolysis Effects
- 2020
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In: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; , s. 1-11
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Journal article (peer-reviewed)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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