| 1. |
- Börjesson Sandén, Fredrik, 1995, et al.
(author)
-
Effects of boric acid on volatile tellurium in severe accident conditions
- 2024
-
In: Annals of Nuclear Energy. - 0306-4549 .- 1873-2100. ; 200
-
Journal article (peer-reviewed)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.
|
|
| 2. |
- Dickinson, S., et al.
(author)
-
Experimental and modelling studies of iodine oxide formation and aerosol behaviour relevant to nuclear reactor accidents
- 2014
-
In: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 74, s. 200-207
-
Journal article (peer-reviewed)abstract
- Plant assessments have shown that iodine contributes significantly to the source term for a range of accident scenarios. Iodine has a complex chemistry that determines its chemical form and, consequently, its volatility in the containment. If volatile iodine species are formed by reactions in the containment, they will be subject to radiolytic reactions in the atmosphere, resulting in the conversion of the gaseous species into involatile iodine oxides, which may deposit on surfaces or re-dissolve in water pools. The concentration of airborne iodine in the containment will, therefore, be determined by the balance between the reactions contributing to the formation and destruction of volatile species, as well as by the physicochemical properties of the iodine oxide aerosols which will influence their longevity in the atmosphere. This paper summarises the work that has been done in the framework of the EC SARNET (Severe Accident Research Network) to develop a greater understanding of the reactions of gaseous iodine species in irradiated air/steam atmospheres, and the nature and behaviour of the reaction products. This work has mainly been focussed on investigating the nature and behaviour of iodine oxide aerosols, but earlier work by members of the SARNET group on gaseous reaction rates is also discussed to place the more recent work into context.
|
|
| 3. |
- Dickinson, S., et al.
(author)
-
Recent advances on containment iodine chemistry
- 2010
-
In: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 52:1, s. 128-135
-
Conference paper (peer-reviewed)abstract
- The 5th FWP EURSAFE Project highlighted iodine chemistry in the containment as one of the issues requiring further research in order to reduce source term uncertainties. Consequently, a series of studies was launched in the 6th FWP SARNET Project aimed at improving the predictability of iodine behaviour during severe accidents via a better understanding of the complex chemical phenomena in the containment. In particular, SARNET has striven to foster common interpretation of integral and separate effect test data, production of new or improved models where necessary, and compilation of the existing knowledge of the subject. The work has been based on a substantial amount of experimental information made available from bench-scale projects (PARIS and EPICUR), via intermediate-scale tests (CAIMAN) to large-scale facilities (SISYPHE, THAI and PHEBUS-FP). In the experimental field, particular attention has been paid to two specific issues: the effects of radiation on both aqueous and gaseous iodine chemistry, and the mass transfer of iodine between aqueous and gaseous phases. Comparisons between calculations and results of the EPICUR and CAIMAN experiments suggest that the aqueous phase chemistry is reasonably well understood, although there are still some areas of uncertainty. Interpretation of integral experiments, like PHEBUS-FPT2, indicated that radiation-induced conversion of molecular iodine into particulate species (IxOy) could be responsible for the gaseous iodine depletion observed in the long-term. However, the results of much simpler, small-scale experiments have shown that further improvements in understanding and modelling are still needed. Mass transfer modelling has been extended to cover evaporating sump conditions based on SISYPHE data; however, application of this model to the larger scale THAI experiments seems not to be straightforward. In addition to these two major issues, some specific studies have been carried out concerning the potential effect of passive autocatalytic hydrogen recombiners on iodine volatility. The RECI analytical experiments have shown that metal iodides (namely Csl and Cdl(2)) are not stable and yield gaseous iodine when heated, in a humid atmosphere, at temperatures representative of recombiner operation. Another important undertaking successfully carried out has been the compilation of an Iodine Data Book, which provides a critical review of the experimental data and modelling approaches that have been used in the development of iodine source term methodologies. This should assist in a proper use of such models, and inform their future development.
|
|
| 4. |
- Espegren, Fredrik, 1989, et al.
(author)
-
Tellurium transport in the RCS under conditions relevant for severe nuclear accidents
- 2021
-
In: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 139
-
Journal article (peer-reviewed)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.
|
|
| 5. |
- Kajan, Ivan, 1984, et al.
(author)
-
Effect of nitrogen compounds on transport of ruthenium through the RCS
- 2017
-
In: Journal of Radioanalytical and Nuclear Chemistry. - : Springer Science and Business Media LLC. - 0236-5731 .- 1588-2780. ; 311:3, s. 2097-2109
-
Journal article (peer-reviewed)abstract
- Ruthenium is a fission product that can be released from the fuel in case of a severe nuclear accident. In this work the impact of the atmosphere composition, including air radiolysis products, on the transport of ruthenium through a primary circuit was examined. Experiments were performed at temperatures 1300, 1500 and 1700 K in a slightly humid air. In the experiments significant effect of nitrogen oxides (N2O, NO2) and nitric acid on the ruthenium chemistry in the model primary circuit was observed. The obtained results indicate a strong effect of air radiolysis products on the quantity partitioning of transported ruthenium to gaseous and aerosol compounds.
|
|
| 6. |
- Kajan, Ivan, 1984, et al.
(author)
-
Impact of Ag and NOx compounds on the transport of ruthenium in the primary circuit of nuclear power plant in a severe accident
- 2017
-
In: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 100, s. 9-19
-
Journal article (peer-reviewed)abstract
- Ruthenium is a semi-volatile element originating as a fission product in nuclear reactors that can be released in case of a severe nuclear accident. In this work, the impact of atmosphere composition on the transport of ruthenium through the primary circuit was examined. The effects of silver nanoparticles representing aerosols and NO2 gas as a product of air radiolysis were studied. Quantification of ruthenium transported both as gas and aerosol was performed. Chemical composition of ruthenium species was evaluated. The transport of gaseous ruthenium through the facility increased significantly when NO2 gas was fed into the atmosphere. When both silver aerosols and NO2 were fed into the atmosphere, the transport of ruthenium in gaseous and aerosol forms was promoted. It was concluded that the composition of atmosphere in the primary circuit will have a notable effect on the speciation of ruthenium transported into the containment building during a severe accident and thus on the potential radioactive release to the environment.
|
|
| 7. |
- Karkela, T., et al.
(author)
-
RECENT FINDINGS ON RUTHENIUM CHEMISTRY IN A SEVERE ACCIDENT
- 2015
-
In: Proceedings of the International OECD-NEA/NUGENIA-SARNET Workshop on the Progress in Iodine Behaviour for NPP Accident Analysis and Management.
-
Conference paper (other academic/artistic)abstract
- The chemistry of radiotoxic ruthenium in a severe nuclear power accident has actively been investigated especially during the last decades. The Ru studies have covered the release from a fuel, the transport in the primary circuit and the behaviour in the containment building. The gathered experimental data have been utilized to understand the key parameters governing the Ru chemistry in a severe accident (SA) and to check the ability of the existing models of SA analysis codes to explain the experimental results. To further increase the knowledge on Ru behaviour, the collaboration on international level has been intensive. Lately, the widest and most active networks have been EU SARNET and EU SARNET2. The valuable effort of these networks on sharing information of e.g. national programs and on interpreting the experimental results is continued in EU NUGENIA program. More detailed studies on separate phenomena have been conducted e.g. as part of OECD/NEA STEM/START and ISTP/VERDON programs. Furthermore, Phébus FP tests have produced valuable data on integral phenomena.The large-scale integral and semi-integral experiments have confirmed that Ru release depends strongly on carrier gas. Ru is significantly released from an irradiated fuel sample under oxidizing conditions, in particular when air is involved. In addition, the oxidation of UO2 fuel seems to lead to a higher Ru release than in case of MOX fuel. Ruthenium can be transported to the containment atmosphere both in gaseous and particulate forms. The small-scale separate-effect experiments gave a detailed view on Ru transport. A high fraction of ruthenium was detected as particles at the outlet of the model primary circuit in an air atmosphere. However, the observed gaseous Ru fraction is higher than what could be expected based on thermodynamic equilibrium calculations. Further studies on the effect of flow residence time in a temperature gradient for the equilibrium of Ru oxides have been conducted.The effect of other fission products in the gas phase, as well as FP deposits on the surface of primary circuit, on the Ru transport has been investigated. For example, caesium containing deposits seemed to trap gaseous ruthenium effectively. Similarly in case of control rod residues, silver particles in the gas phase of the circuit acted as a sink for gaseous Ru. In an air ingress accident, the effect of air radiolysis products on the Ru chemistry becomes important. As the main air radiolysis products can be considered as oxidizing agents, their ability to oxidize the lower oxides of Ru to higher oxidation state has been examined.Most of Ru in the containment building ends up as deposits on the containment surfaces and in the sump. Experiments on the radiolytical revaporisation of ruthenium deposits on the epoxy paint surface indicated the release of gaseous ruthenium and it was enhanced under humid atmosphere and elevated temperature. It appeared that the products of air radiolysis caused by γ-radiation promoted the formation of gaseous ruthenium from Ru oxide deposits on paint in a higher amount than could be expected by pure ozone action. Concerning the irradiation tests of perruthenate aqueous solutions, they indicated the formation of gaseous Ru by γ-radiolysis products in solution.
|
|
| 8. |
- Karkela, T., et al.
(author)
-
Ruthenium transport in an RCS with airborne CsI
- 2017
-
In: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 99, s. 38-48
-
Journal article (peer-reviewed)abstract
- Ruthenium is one of the most radiotoxic fission products which can be released from fuel as ruthenium oxides in an air ingress accident at a nuclear power plant. In this study it was found that the transport of the released ruthenium oxides through a reactor coolant system into the containment building is significantly affected by the atmospheric conditions. Airborne CsI increased the transport of gaseous ruthenium compared with that in a pure air atmosphere. The overall transport of ruthenium increased with temperature. In order to understand the behaviour of ruthenium in accident conditions, it is important to widen the experimental conditions from pure air/steam atmospheres to more realistic mixtures of prototypic gases and aerosols.
|
|
| 9. |
- Karkela, T., et al.
(author)
-
Tellurium retention by containment spray system
- 2021
-
In: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 164
-
Journal article (peer-reviewed)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.
|
|
| 10. |
- Kučera, Jan, et al.
(author)
-
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
-
In: Microchemical Journal. - : Elsevier BV. - 0026-265X. ; 158
-
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.
|
|
