| 1. |
- Ali, Yusuf, et al.
(författare)
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Experimental determination of concentration factors of Ni, Ru and Sb in the model diatom Phaeodactylum tricornutum
- 2023
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Ingår i: Scientific Reports. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the experimental determination of concentration factors (CF) for nickel, ruthenium and antimony in the model diatom Phaeodactylum tricornutum Bohlin (Bacillariophyceae), which was chosen as a representative of marine phytoplankton. Better determinations of these CF are needed to improve the modelling of marine ecosystems at release points, where radioactive pollutants enter the ecosystem, for more accurate predictions of radiation dose to humans caused by these pollutants. A literature study revealed that the currently implemented values of these CF are based on very scarce data, and a computational sensitivity study showed that the radiation dose caused by radioisotopes of these elements depend strongly on the phytoplankton CF. Nutrient-enriched water samples from Swedish coastal waters were used as a medium for growing of the diatom species P. tricornutum and radioactive isotopes of the studied elements were added to the cultures during the exponential growth phase. The radioactivity in the P. tricornutum and in the culture medium were measured separately and used for determination of CF. Conservative estimates of the CF based on this phytoplankton proxy on the present data are 6400 L/kg for nickel, 20,000 L/kg for ruthenium and 890 L/kg for antimony, with P. tricornutum biomass masses referring to dry weight. The estimates for nickel and ruthenium are similar to previously published values, which underpins the credibility of radiation dose calculations based on these values. The estimate for antimony is uncertain, but also, to our knowledge, represents the first published experimentally based data on this CF.
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| 2. |
- Drera, S. S., et al.
(författare)
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Thorium fuel production and results from beginning of life irradiation
- 2014
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Ingår i: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 72, s. 5-10
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Tidskriftsartikel (refereegranskat)abstract
- An evolutionary, rather than a revolutionary approach to thorium fueled reactors is proposed with an introduction of thorium as the fertile component in mixed oxide fuel for conventional light water reactors. The utility of thorium as a component in today's light water reactors offers improved accident tolerance due to the superior material properties of thorium fuels over conventional uranium fuels. A few notable advantages include better thermal conductivity, higher melting point, higher oxide stability and superior spent fuel characteristics. Consequently, Thor Energy along with a consortium of industrial partners has established a fuel production and irradiation program aimed to license thorium fuels for use in today's light water reactors: Due to the morphology and physical properties of calcined thorium oxide powder, pellet fabrication used for standard uranium oxide fuels must be altered slightly for thorium bearing fuels to yield a product with acceptable theoretical densities, microstructure, and material integrity. At beginning of irradiation life fuel temperature data demonstrates improved fuel characteristics over standard uranium oxide fuel. Fuel centerline operating temperatures are 30-40 K less with a thorium mixed oxide fuel as compared to standard uranium fuel. (c) 2013 Elsevier Ltd. All rights reserved.
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| 3. |
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| 4. |
- Insulander Björk, Klara, 1982, et al.
(författare)
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Effect of the thorium oxide content on the leaching of a mixed thorium-uranium oxide fuel
- 2022
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Ingår i: Journal of Radioanalytical and Nuclear Chemistry. - : Springer Science and Business Media LLC. - 0236-5731 .- 1588-2780. ; 331, s. 2849-2857
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Tidskriftsartikel (refereegranskat)abstract
- Leaching of uranium from uranium oxide fuel in contact with water can be a radiation hazard problem in the case of fuel cladding failure, either during nuclear reactor operation or in an interim storage, as well as in a final repository. One way to mitigate this is to reduce the solubility of the fuel matrix by the mixing uranium oxide with a compound which is less soluble but otherwise of similar properties. In this paper, the effect of thorium oxide content on the leaching of the uranium oxide matrix is investigated. The method was to study the leaching of the uranium oxide fuel matrix as a function of a varying content of thorium oxide, using materials manufactured by powder co-milling. It was found that the substitution of more than 25% UO2 with ThO2 reduces the matrix leaching by more than one order of magnitude in most of the different leaching solutions investigated. The substitution of 7% UO2 with ThO2 results in a reduction of matrix leaching by 10–90%, depending on the concentration of borate and dissolved oxygen in the leaching solution.
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| 5. |
- Insulander Björk, Klara, 1982, et al.
(författare)
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Experimental determination of concentration factors of Mn, Zn and I in the phytoplankton species Phaeodactylum Tricornutum
- 2023
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Ingår i: Journal of Environmental Radioactivity. - : Elsevier BV. - 0265-931X .- 1879-1700. ; 261
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic radionuclides released into the environment cause a radiation dose to wildlife and humans which must be quantified, both to assess the effect of normal releases, and to predict the consequences of a larger, unplanned release. To estimate the spread of the radioactive elements, the ecosystem around release points is modelled, and element uptake is usually quantified by concentration factors (CF), which relates the concentration of an element in an organism to the concentration of the same element in a medium under equilibrium conditions. In this work, we experimentally determine some phytoplankton CF that are needed for improved modelling of the marine ecosystems around nuclear facilities and release points. CFs that require better determination have been identified through literature search. Sensitivity studies, using the currently used ecosystem modelling software PREDO, show that for most studied groups, the dose committed by the respective radionuclides is almost proportional to the corresponding phytoplankton CFs. In the present work, CFs are determined through laboratory experiments with cultured phytoplankton and radionuclides of the concerned elements, assessing the element uptake by the phytoplankton through detection of the emitted radiation. The three CF assessed in this work were those for manganese, zinc and iodine in phytoplankton. Conservative estimates of these CF based on the present data are 40 000 L/kg for manganese, 50 000 L/kg for zinc and 180 L/kg for iodine with the phytoplankton masses referring to their dry weight.
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| 6. |
- Insulander Björk, Klara, 1982, et al.
(författare)
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Kinetic modelling of runaway electron generation in argon-induced disruptions in ASDEX Upgrade
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:4
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Tidskriftsartikel (refereegranskat)abstract
- Massive material injection has been proposed as a way to mitigate the formation of a beam of relativistic runaway electrons that may result from a disruption in tokamak plasmas. In this paper we analyse runaway generation observed in eleven ASDEX Upgrade discharges where disruption was triggered using massive gas injection. We present numerical simulations in scenarios characteristic of on-axis plasma conditions, constrained by experimental observations, using a description of the runaway dynamics with a self-consistent electric field and temperature evolution in two-dimensional momentum space and zero-dimensional real space. We describe the evolution of the electron distribution function during the disruption, and show that the runaway seed generation is dominated by hot-tail in all of the simulated discharges. We reproduce the observed dependence of the current dissipation rate on the amount of injected argon during the runaway plateau phase. Our simulations also indicate that above a threshold amount of injected argon, the current density after the current quench depends strongly on the argon densities. This trend is not observed in the experiments, which suggests that effects not captured by zero-dimensional kinetic modelling - such as runaway seed transport - are also important.
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| 7. |
- Insulander Björk, Klara L, 1982
(författare)
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A BWR fuel assembly design for efficient use of plutonium in thorium–plutonium fuel
- 2013
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Ingår i: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 65, s. 56-63
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study is to develop an optimized BWR fuel assembly design for thorium–plutonium fuel. In this work, the optimization goal is to maximize the amount of energy that can be extracted from a certain amount of plutonium, while maintaining acceptable values of the neutronic safety parameters such as reactivity coefficients, shutdown margins and power distribution. The factors having the most significant influence on the neutronic properties are the hydrogen-to-heavy-metal ratio, the distribution of the moderator within the fuel assembly, the initial plutonium fraction in the fuel and the radial distribution of the plutonium in the fuel assembly. The study begins with an investigation of how these factors affect the plutonium requirements and the safety parameters. The gathered knowledge is then used to develop and evaluate a fuel assembly design. The main characteristics of this fuel design are improved Pu efficiency, very high fractional Pu burning and neutronic safety parameters compliant with current demands on UOX fuel.
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| 8. |
- Insulander Björk, Klara L, 1982, et al.
(författare)
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Commercial thorium fuel manufacture and irradiation: Testing (Th,Pu)O-2 and (Th,U)O-2 in the "Seven-Thirty" program
- 2015
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 75, s. 79-86
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Tidskriftsartikel (refereegranskat)abstract
- Thorium based fuels are being tested in the Halden Research Reactor in Norway with the aim of producing the data necessary for licensing of these fuels in today's light water reactors. The fuel types currently under irradiation are thorium oxide fuel with plutonium as the fissile component, and uranium fuel with thorium as an additive for enhancement of thermo-mechanical and neutronic fuel properties. Fuel temperatures, rod pressures and dimensional changes are monitored on-line for quantification of thermo-mechanical behavior and fission gas release. Preliminary irradiation results show benefits in terms of lower fuel temperatures, mainly caused by improved thermal conductivity of the thorium fuels. In parallel with the irradiation, a manufacturing procedure for thorium-plutonium mixed oxide fuel is developed with the aim to manufacture industrially relevant high-quality fuel pellets for the next phase of the irradiation campaign.
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| 9. |
- Insulander Björk, Klara L, 1982, et al.
(författare)
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Comparison of thorium-based fuels with different fissile components in existing boiling water reactors
- 2011
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Ingår i: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 53:6, s. 618-625
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Tidskriftsartikel (refereegranskat)abstract
- With the aim of investigating the technical feasibility of fuelling a conventional BWR (Boiling Water Reactor) with thorium-based fuel, computer simulations were carried out in a 2D infinite lattice model using CASMO-5. Four different fissile components were each homogenously combined with thorium to form mixed oxide pellets: Uranium enriched to 20% U-235 (LEU), plutonium recovered from spent LWR fuel (RGPu), pure U-233 and a mixture of RGPu and uranium recovered from spent thorium-based fuel. Based on these fuel types, four BWR nuclear fuel assembly designs were formed, using a conventional assembly geometry (GE14-N). The fissile content was chosen to give a total energy release equivalent to that of a UOX fuel bundle reaching a discharge burnup of about 55 MWd/kgHM. The radial distribution of fissile material was optimized to achieve low bundle internal radial power peaking. Reactor physical parameters were computed, and the results were compared to those of reference LEU and MOX bundle designs. It was concluded that a viable thorium-based BWR nuclear fuel assembly design, based on any of the fissile components, can be achieved. Neutronic parameters that are essential for reactor safety, like reactivity coefficients and control rod worths, are in most cases similar to those of LEU and MOX fuel. This is also true for the decay heat produced in irradiated fuel. However when Th is mixed with U-233, the void coefficient (calculated in 2D) can be positive under some conditions. It was concluded that it is very difficult to make savings of natural uranium by mixing LEU (20% U-235) homogenously with thorium and that mixing RGPu with thorium leads to more efficient consumption of Pu compared to MOX fuel.
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| 10. |
- Insulander Björk, Klara L, 1982, et al.
(författare)
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Comparison of thorium-based fuels with different fissile components in existing boiling water reactors
- 2009
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Ingår i: Proc. Int. Congress on Advances in Nuclear Power Plants (ICAPP '09). ; 3, s. 1982-1987
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Konferensbidrag (refereegranskat)abstract
- Three different types of thorium based BWR fuel have been developed, in each of which thorium was combined with a different fissile component, the three components being reactor grade plutonium, uranium enriched to 20% in uranium 235 and pure uranium 233. A BWR nuclear bundle design, based on the geometrical fuel assembly design GE14, was developed for each of these fissile components. The properties and performance of the corresponding fuel assemblies were investigated via full core calculations carried out for an existing BWR and compared with the ones of an ordinary Low Enriched Uranium (LEU) fuel, which was developed for reference. The fuel assemblies and cores were designed to meet existing fuel design criteria, and were then analyzed with regards to reactivity coefficients, delayed neutron fractions, control rod worths and shutdown margins. The results show that all three alternatives seem to be feasible, although some difficulties remain with complying with the thermal limits, and with the moderator temperature and coolant void coefficients of the U-233 containing fuel being positive under some circumstances.
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