PGET Monte Carlo simulations using Serpent

Since 2017, over 100 spent nuclear fuel assemblies at the Finnish nuclear power plants have been imaged with the Passive Gamma Emission Tomography (PGET) device in preparation of the implementation of PGET in the safeguards infrastructure of the Finnish geological repository. In order to increase understanding of the PGET method and guide its further development, we have recently implemented PGET in Serpent, a widely-used neutron and photon transport Monte Carlo simulation code. We will discuss the major aspects of this implementation and illustrate the usefulness of the simulations with a few examples. The PGET device as used in the measurements (which was developed under the guidance of IAEA and is approved for safeguards inspections) was implemented in a very realistic way based on its technical drawings. The simulation produces sinograms in user-defined energy windows as well as the uncertainty on these sinograms. Tomographic images are then reconstructed using the exact same algorithm as used for the measured data. A dedicated variance reduction scheme was implemented, increasing the computational efficiency by about a factor of 30. The simulation of the PGET response at one angular measurement position for 1 billion primary photons takes a few hours on a single 40-core node. The 1-sigma uncertainty in the highest intensity sinogram pixels is about a few percent. Aiming at improving the imaging of VVER-440 assemblies, we have simulated assemblies containing one or a few missing fuel rods or having only one emitting rod (the other rods being present but not emitting) in various well-chosen places, configurations that are not accessible in practice. The single-emitting rod results show in great detail those parts of the sinogram that contain most of the information for the particular rod position. How this information might be used for obtaining better images, especially of the central region of a fuel assembly, will be discussed

PGET Monte Carlo simulations using Serpent

Since 2017, over 100 spent nuclear fuel assemblies at the Finnish nuclear power plants have been imaged with the Passive Gamma Emission Tomography (PGET) device in preparation of the implementation of PGET in the safeguards infrastructure of the Finnish geological repository. In order to increase understanding of the PGET method and guide its further development, we have recently implemented PGET in Serpent, a widely-used neutron and photon transport Monte Carlo simulation code. We will discuss the major aspects of this implementation and illustrate the usefulness of the simulations with a few examples. The PGET device as used in the measurements (which was developed under the guidance of IAEA and is approved for safeguards inspections) was implemented in a very realistic way based on its technical drawings. The simulation produces sinograms in user-defined energy windows as well as the uncertainty on these sinograms. Tomographic images are then reconstructed using the exact same algorithm as used for the measured data. A dedicated variance reduction scheme was implemented, increasing the computational efficiency by about a factor of 30. The simulation of the PGET response at one angular measurement position for 1 billion primary photons takes a few hours on a single 40-core node. The 1-sigma uncertainty in the highest intensity sinogram pixels is about a few percent. Aiming at improving the imaging of VVER-440 assemblies, we have simulated assemblies containing one or a few missing fuel rods or having only one emitting rod (the other rods being present but not emitting) in various well-chosen places, configurations that are not accessible in practice. The single-emitting rod results show in great detail those parts of the sinogram that contain most of the information for the particular rod position. How this information might be used for obtaining better images, especially of the central region of a fuel assembly, will be discussed

In-air and in-water performance comparison of Passive Gamma Emission Tomography with activated Co-60 rods

Abstract A first-of-a-kind geological repository for spent nuclear fuel is being built in Finland and will soon start operations. To make sure all nuclear material stays in peaceful use, the fuel is measured with two complementary non-destructive methods to verify the integrity and the fissile content of the fuel prior to disposal. For pin-wise identification of active fuel material, a Passive Gamma Emission Tomography (PGET) device is used. Gamma radiation emitted by the fuel is assayed from 360 angles around the assembly with highly collimated CdZnTe detectors, and a 2D cross-sectional image is reconstructed from the data. At the encapsulation plant in Finland, there will be the possibility to measure in air. Since the performance of the method has only been studied in water, measurements with mock-up fuel were conducted at the Atominstitut in Vienna, Austria. Four different arrangements of activated Co-60 rods, steel rods and empty positions were investigated both in air and in water to confirm the functionality of the method. The measurement medium was not observed to affect the ability of the method to distinguish modified rod positions from filled rod positions. More extended conclusions about the method performance with real spent nuclear fuel cannot be drawn from the mock-up studies, since the gamma energies, activities, material attenuations and assembly dimensions are different, but full-scale measurements with spent nuclear fuel are planned for 2023

Improved Passive Gamma Emission Tomography image quality in the central region of spent nuclear fuel

Reliable non-destructive methods for verifying spent nuclear fuel are essential to draw credible nuclear safeguards conclusions from spent fuel. In Finland, spent fuel items are verified prior to the soon starting disposal in a geological repository with Passive Gamma Emission Tomography (PGET), a uniquely accurate method capable of rod-level detection of missing active material. The PGET device consists of two highly collimated detector banks, collecting gamma emission data from a 360 degrees rotation around a fuel assembly. 2D cross-sectional activity and attenuation images are simultaneously computed. We present methods for improving reconstructed image quality in the central parts of the fuel. The results are based on data collected from 2017 to 2021 at the Finnish nuclear power plants with 10 fuel assembly types of varying characteristics, for example burnups from 5.7 to 55 GWd/tU and cooling times from 1.9 to 37 years. Data is acquired in different gamma energy windows, capturing the peaks of Cs-137 (at 662 keV) and Eu-154 (at 1274 keV), abundant isotopes in long-cooled spent nuclear fuel. Data from these gamma energy windows at well-chosen angles are used for higher-quality images, resulting in more accurate detection of empty rod positions. The method is shown to detect partial diversion of nuclear material also in the axial direction, demonstrated with a novel measurement series scanning over the edge of partial-length rods.Peer reviewe

Lactobacillus rhamnosus GG Intake Modifies Preschool Children's Intestinal Microbiota, Alleviates Penicillin-Associated Changes, and Reduces Antibiotic Use

Antibiotic use is considered among the most severe causes of disturbance to children's developing intestinal microbiota, and frequently causes adverse gastrointestinal effects ranging from mild and transient diarrhoea to life-threatening infections. Probiotics are commonly advocated to help in preventing antibiotic-associated gastrointestinal symptoms. However, it is currently unknown whether probiotics alleviate the antibiotic-associated changes in children's microbiota. Furthermore, it is not known how long-term probiotic consumption influences the developing microbiota of children. We analysed the influence of long-term Lactobacillus rhamnosus GG intake on preschool children's antibiotic use, and antibiotic-associated gastrointestinal complaints in a double blind, randomized placebo-controlled trial with 231 children aged 2-7. In addition, we analysed the effect of L. rhanmosus GG on the intestinal microbiota in a subset of 88 children. The results show that long-term L. rhamnosus GG supplementation has an influence on the composition of the intestinal microbiota in children, causing an increase in the abundance of Prevotella, Lactococcus, and Ruminococcus, and a decrease in Escherichia. The treatment appeared to prevent some of the changes in the microbiota associated with penicillin use, but not those associated with macrolide use. The treatment, however, did reduce the frequency of gastrointestinal complaints after a macrolide course. Finally, the treatment appeared to prevent certain bacterial infections for up to 3 years after the trial, as indicated by reduced antibiotic use.Peer reviewe

Intestinal microbiome is related to lifetime antibiotic use in Finnish pre-school children

Early-life antibiotic use is associated with increased risk for metabolic and immunological diseases, and mouse studies indicate a causal role of the disrupted microbiome. However, little is known about the impacts of antibiotics on the developing microbiome of children. Here we use phylogenetics, metagenomics and individual antibiotic purchase records to show that macrolide use in 2-7 year-old Finnish children (N = 142; sampled at two time points) is associated with a long-lasting shift in microbiota composition and metabolism. The shift includes depletion of Actinobacteria, increase in Bacteroidetes and Proteobacteria, decrease in bile-salt hydrolase and increase in macrolide resistance. Furthermore, macrolide use in early life is associated with increased risk of asthma and predisposes to antibiotic-associated weight gain. Overweight and asthmatic children have distinct microbiota compositions. Penicillins leave a weaker mark on the microbiota than macrolides. Our results support the idea that, without compromising clinical practice, the impact on the intestinal microbiota should be considered when prescribing antibiotics.Peer reviewe

Suomi arktisen alueen vastuulliseksi edelläkävijäksi

Toimenpide-ehdotuksia yleisen kehityksen, meriklusterin ja matkailun edistämiseksi vuoteen 2035 Raportti esittää MERMAID-hankkeessa kehitettyjä Suomelle olennaisia suosituksia ja toimenpiteitä arktisen alueen yleisen kehityksen ja liiketoiminnan edistämiseksi, keskittyen erityisesti meri- ja matkailusektoreille, vuoteen 2035 asti. Raportissa on myös analyysi Venäjän arktisesta energiapolitiikasta akateemisen kirjallisuuden ja media-analyysin pohjalta. Arktisen alueen yleisen kehityksen edistämiseksi tulisi mm. nostaa arktisen luonnonsuojelun kansallista prioriteettia, luoda kannustavat puitteet kansalliselle arktiselle liiketoiminnalle ja lisätä kansainvälisten arktisten investointimarkkinoiden avoimuutta. Merenkulun osalta suositellaan mm. yhteistyön lisäämistä meriklusterin ja energian- ja raaka-ainetuotannon välillä ja perustamaan offshore- ja subsea-osaamisen koulutusohjelma. Matkailualalla tulisi mm. hyödyntää kokemukset ja osaaminen arktisessa arjessa esim. brändäämällä Arctic is cool -ajatus ja kehittää arktisen alueen matkailutoimijoiden osaamista. Hanke suosittelee myös avointa yhteistyötä ja osaamisen jakamista Venäjän kanssa. Venäjän keskeisin mielenkiinnon kohde arktisella alueella on hiilivetyjen hyödyntäminen, mutta maan energiahankkeita tulee arvioida taloudellisen kannattavuuden lisäksi myös poliittisten intressien näkökulmasta. Ilmastonmuutoksen vaikutusten monimutkaisuus asettaa kuitenkin rajoitteita arktisella alueella toimimiselle. Suositusten vaikutukset, onnistumisen edellytykset ja riskit on analysoitu hankkeessa muodostettujen kolmen tulevaisuuskuvan mukaisesti

Finland’s journey toward the Forefront of Responsible Arctic Development : Suggestions for General Development, Maritime Cluster and Tourism Measures by 2035

Raportti esittää MERMAID-hankkeessa kehitettyjä Suomelle olennaisia suosituksia ja toimenpiteitä arktisen alueen yleisen kehityksen ja liiketoiminnan edistämiseksi, keskittyen erityisesti meri- ja matkailusektoreille, vuoteen 2035 asti. Raportissa on myös analyysi Venäjän arktisesta energiapolitiikasta akateemisen kirjallisuuden ja media-analyysin pohjalta. Arktisen alueen yleisen kehityksen edistämiseksi tulisi mm. nostaa arktisen luonnonsuojelun kansallista prioriteettia, luoda kannustavat puitteet kansalliselle arktiselle liiketoiminnalle ja lisätä kansainvälisten arktisten investointimarkkinoiden avoimuutta. Merenkulun osalta suositellaan mm. yhteistyön lisäämistä meriklusterin ja energian- ja raaka-ainetuotannon välillä ja perustamaan offshore- ja subsea-osaamisen koulutusohjelma. Matkailualalla tulisi mm. hyödyntää kokemukset ja osaaminen arktisessa arjessa esim. brändäämällä Arctic is cool -ajatus ja kehittää arktisen alueen matkailutoimijoiden osaamista. Hanke suosittelee myös avointa yhteistyötä ja osaamisen jakamista Venäjän kanssa. Venäjän keskeisin mielenkiinnon kohde arktisella alueella on hiilivetyjen hyödyntäminen, mutta maan energiahankkeita tulee arvioida taloudellisen kannattavuuden lisäksi myös poliittisten intressien näkökulmasta. Ilmastonmuutoksen vaikutusten monimutkaisuus asettaa kuitenkin rajoitteita arktisella alueella toimimiselle. Suositusten vaikutukset, onnistumisen edellytykset ja riskit on analysoitu hankkeessa muodostettujen kolmen tulevaisuuskuvan mukaisesti.This report presents the recommendations and measures for Finland’s journey toward responsible Arc- tic development, as identified in the MERMAID-project. The focus is on general issues and business, with a special focus on the maritime cluster and tourism sector. Furthermore, the report presents an analysis of the Russian Arctic energy policy based on academic literature and media-analysis. To further the general development of the Arctic, the project recommends, inter alia, increasing the na- tional priority of environmental protection, creating a supportive environment for national Arctic business and commerce, and increasing the openness of the international Arctic investment markets. To further the maritime sector, the project recommends, inter alia, increasing the collaboration between the mari- time cluster and energy and resource extraction sectors, and creating an offshore and subsea educa- tion programme. To further the tourism sector, the project recommends, inter alia, utilizing the experi- ences and knowledge in the everyday Arctic by e.g. branding the idea ‘Arctic is Cool’ and increasing the know-how of Arctic tourism operators. The project also recommends open collaboration and knowledge sharing with Russia. Russia’s main interest in the Arctic is the utilization of hydrocarbons, but the Russian energy projects should be as- sessed not only from economic perspective, but also from political viewpoint. However, the complicated nature of climate change impacts are posing restrictions on operating in the Arctic. The consequences of the recommendations, the conditions for successful implementation, and risks have been analysed with respect to the three future scenarios constructed during the project

Litiumnikkelisinkkioksidi-yksikomponenttipolttokennon suorituskyvyn optimointi kennon koostumusta muuttamalla

Fuel cells are electrochemical devices that convert hydrogen and oxygen into electricity and water. They enable sustainable energy production and are a topic of immense research. Single component fuel cells are an emerging type of fuel cells that have many advantages over traditional three-layered cells but their working mechanisms are not yet fully understood. Single component fuel cells are easy to manufacture. Furthermore, they are expected to have better thermal stability than conventional three-layered cells, which might suffer from a mismatch in the thermal coefficients between the different layers, which results in cracking during high temperature operation. This work focuses on screening different ionic conductor – semiconductor compositions for single component fuel cells to optimize the cell performance. LiNiZn-oxide– Gd doped Ce2O (LNZ-GDC) cells are fabricated in different compositions ranging from pure LNZ to pure GDC in 20% increments. X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and current-voltage (IV) measurement techniques are used for characterizing the cell crystal structure, impedance behavior and performance. In addition, the optimal cell composition, which yields the highest power density, is studied for temperature and gas atmosphere effects as well as cell porosity effects. The most commonly used composition of 40wt% LNZ, 60wt% GDC is proven to be the most efficient, yielding a power density of 30 mW/cm2at 550◦C. Increasing operating temperature reduces cell resistance and increases ionic conduction. Gas atmosphere is observed to have several complicated effects on the cell performance. Recommendations for standardized stabilization times and active area requirements are given. In the future, single component fuel cells should be systematically studied for long-term stability to identify the degradation mechanisms in the cells, since only a stable and high performance cell can be commercialized