Synthesis and characterization of homogeneous (U,Am)O₂ and (U,Pu,Am)O₂ nanopowders

This paper details the first dedicated production of homogeneous nanocrystalline particles of mixed actinide oxide solid solutions containing americium. The target compositions were $U_{0.75}Pu_{0.20}Am_{0.05}O_{2}$, $U_{0.90}Am_{0.10}O_{2}$ and $U_{0.80}Am_{0.20}O_{2}$. After successful hydrothermal synthesis and chemical characterisation, the nanocrystals were sintered and their structure and behaviour under self-irradiation were studied by powder XRD. Cationic charge distribution of the as-prepared nanocrystalline and sintered $U_{0.80}Am_{0.20}O_{2}$ materials was investigated applying $U M_{4}$ and $Am M_{5}$ edge high energy resolution XANES (HR-XANES). Typical oxidation states detected for the cations are $U_{(IV)}/U_{(V)}$ and $Am_{(III)}/Am_{(IV)}$. The measured crystallographic swelling was systematically smaller for the as-synthesised nanoparticles than the sintered products. For sintered pellets, the maximal volumetric swelling was about 0.8% at saturation, in line with literature data for $PuO_{2}$, $AmO_{2}$, $(U,Pu)O_{2}$ or $(U,Am)O_{2}$

Cytokines in relation to hCG are significantly altered in asymptomatic women with miscarriage – a pilot study

Background: Spontaneous abortion is one of the most common complications in early pregnancy. A preventive test to identify women who will experience a miscarriage, even before first symptoms occur, is not established. Activation of maternal immunological tolerance seems to be essential for early fetal development and various cytokines have been described in different stages of pregnancy. Therefore, we aimed to investigate if chemokine levels at the time of pregnancy testing relative to human Choriogonadotropin (hCG) are altered in patients who will experience a miscarriage in this pregnancy. Methods: We obtained blood samples from 39 women. Dependent on the follow-up, patients with a positive pregnancy test were subsequently divided in two groups: ongoing pregnancy (n = 22) and miscarriage (n = 17) in this pregnancy. Immunological and endocrine profiling of maternal plasma at the time of pregnancy testing (5th week of gestation) was performed for each group at the time of pregnancy test using Multiplex and ELISA analysis. Results: hCG was significantly decreased in patients with abortion whereas levels of IL-1ra, MIP-1a and TNF-alpha were significantly increased. GCSF/ IL-1ra-ratio was 1.66-fold increased in patients with ongoing pregnancy. TGF-beta /MIP1a-ratio was significantly 3.45-times higher in patients with miscarriage. Comparing patients with ongoing pregnancy to patients experiencing a miscarriage, we could demonstrate significant alterations of the ratios MIP1a/hCG, IL-1ra/hCG, TNFalpha/hCG, MCP1/hCG, IL-6/hCG, TPO/hCG and TGF-beta1/hCG. The strongest effects were seen for the ratio MIP1a/hCG, IL-1ra/hCG and TNFalpha/hCG. Conclusions: We have shown that cytokines in relation to hCG after 4 weeks of gestation are significantly altered in women with miscarriage, promising potential as a prognostic biomarker

Enhanced thermal stability of organic solar cells comprising ternary D-D-A bulk-heterojunctions

Organic solar cells: Polymer mixtures enhance the thermal stability Organic solar cells increase their lifetime by adding another polymer component, paving the way towards commercialization. A team led by Alexander Colsmann at Karlsruhe Institute of Technology, Germany conducted systematic spectroscopic investigations and device characterizations to demonstrate that the degradation of PTB7-Th: PC61BM solar cell can be efficiently suppressed by incorporating the near infrared-absorbing polymer PDTP-DFBT. Upon harsh thermal stress at 120 °C for 2 h, the ternary solar cells show only a minor relative deterioration of 10% with a high power conversion efficiency of 6%. This work reveals the importance of a third component to lock the phase conformation of the polymer and fullerene domains. This is a key step for the thermally stable power output thus the commercialization of the organic solar cells

Störfallsimulationen und Nachbestrahlungsuntersuchungen an kugelförmigen Brennelementen für Hochtemperaturreaktoren

An important aspect of the safety of high temperature reactors is the quality of the nuclear fuel and its ability to remain intact even at high temperatures and to safely contain the radioactive fission products. In combination with a suitable reactor an inherent safety against large release of fission products can be achieved. In this work experimental simulations of severe accidents were conducted on spherical fuel elements for high temperature reactors with TRISO-coated particles and fission productrelease was measured. The fuel elements originated from various irradiation experiments conducted at high temperatures with high burn-up. The experiments were performed using the cold finger apparatus, a test apparatus which was already used in the past in a former version at the Research Center Jülich. The new cold finger apparatus is installed since 2005 in the Hot Cells of the European Institute for Transuranium Elements. The cold finger apparatus at the Institute for Transuranium Elements enabled incident simulations on irradiated high temperature reactor fuel elements in a helium atmosphere at ambient pressure, at temperatures up to 1800 °C and for periods of several hundred hours. Here, both the release of fission gases and the release of solid fission products were measured. In addition, in the context of the present study, the mechanical behavior of the fuel particles and the transport mechanisms of the main fission products were analyzed and the expected release was computed. For a better understanding of the processes post irradiation examinations were conducted on the available fuel elements. It was finally made an assessment of the test results which were compared with results in the existing literature. A key objective of the work was the extension of the existing data base for modern HTR-fuel towards higher burn-up and higher fluences of fast neutrons, higher operating temperatures and extended accident temperatures.JRC.DG.E.2-Hot cell

Störfallsimulationen und Nachbestrahlungsuntersuchungen an kugelförmigen Brennelementen für Hochtemperaturreaktoren

An important aspect of the safety of high temperature reactors is the quality of the nuclear fuel and its ability to remain intact even at high temperatures and to safely contain the radioactive fission products. In combination with a suitable reactor an inherent safety against large release of fission products can be achieved. In this work experimental simulations of severe accidents were conducted on spherical fuel elements for high temperature reactors with TRISO-coated particles and fission product release was measured. The fuel elements originated from various irradiation experiments conducted at high temperatures with high burn-up. The experiments were performed using the cold finger apparatus, a test apparatus which was already used in the past in a former version at the Research Center Jülich. The new cold finger apparatus is installed since 2005 in the Hot Cells of the European Institute for Transuranium Elements. The cold finger apparatus at the Institute for Transuranium enabled incident simulations on irradiated high temperature reactor fuel elements in a helium atmosphere at ambient pressure, at temperatures up to 1800°C and for periods of several hundred hours. Here, both the release of fission gases and the release of solid fission products were measured. In addition, in the context of the present study, the mechanical behavior of the fuel particles and the transport mechanisms of the main fission products were analyzed and the expected release was computed. For a better understanding of the processes post irradiation examinations were conducted on the available fuel elements. It was finally made an assessment of the test results which were compared with results in the existing literature. A key objective of the work was the extension of the existing data base for modern HTR-fuel towards higher burn-up and higher fluences of fast neutrons, higher operating temperatures and extended accident temperatures

Störfallsimulationen und Nachbestrahlungsuntersuchungen an kugelförmigen Brennelementen für Hochtemperaturreaktoren

An important aspect of the safety of high temperature reactors is the quality of the nuclear fuel and its ability to remain intact even at high temperatures and to safely contain the radioactive fission products. In combination with a suitable reactor an inherent safety against large release of fission products can be achieved. In this work experimental simulations of severe accidents were conducted on spherical fuel elements for high temperature reactors with TRISO-coated particles and fission product release was measured. The fuel elements originated from various irradiation experiments conducted at high temperatures with high burn-up. The experiments were performed using the cold finger apparatus, a test apparatus which was already used in the past in a former version at the Research Center Jülich. The new cold finger apparatus is installed since 2005 in the Hot Cells of the European Institute for Transuranium Elements. The cold finger apparatus at the Institute for Transuranium enabled incident simulations on irradiated high temperature reactor fuel elements in a helium atmosphere at ambient pressure, at temperatures up to 1800°C and for periods of several hundred hours. Here, both the release of fission gases and the release of solid fission products were measured. In addition, in the context of the present study, the mechanical behavior of the fuel particles and the transport mechanisms of the main fission products were analyzed and the expected release was computed. For a better understanding of the processes post irradiation examinations were conducted on the available fuel elements. It was finally made an assessment of the test results which were compared with results in the existing literature. A key objective of the work was the extension of the existing data base for modern HTR-fuel towards higher burn-up and higher fluences of fast neutrons, higher operating temperatures and extended accident temperatures

Pruebas de situaciones accidentales en combustible de HTR con el dispositivo Küfa (Accident testing of HTR fuel with the KÜFA device)

The ceramic and ceramic-like coating materials in modern high-temperature reactor fuel are designed to ensure mechanical stability and retention of fission products under normal and transient conditions, regardless of the radiation damage sustained in-pile. In hypothetical depressurization and loss-of-forced-circulation (D LOFC) accidents, fuel elements of modular high-temperature reactors are exposed to temperatures several hundred degrees higher than during normal operation, causing increased thermo-mechanical stress on the coating layers. At the Institute for Transuranium Elements of the European Commission, a vigorous experimental program is being pursued with the aim of characterizing the performance of irradiated HTR fuel under such accident conditions. A cold finger device (Küfa), operational in ITU¿s hot cells since 2006, has been used to perform heating experiments on eight irradiated HTR fuel pebbles from the AVR experimental reactor and from dedicated irradiation campaigns at the High-Flux Reactor in Petten, The Netherlands. Gaseous fission products are collected in a cryogenic charcoal trap, while volatiles are plated out on a water-cooled condensate plate. A quantitative measurement of the release is obtained by gamma spectroscopy. We highlight experimental results from the Küfa testing as well as the on-going development of new experimental facilities.JRC.DG.E.2-Hot cell

FUEL SAFETY INVESTIGATIONS AT THE INSTITUTE OF TRANSURANIUM ELEMENTS

The Institute for Transuranium Elements (JRC-ITU) is one of seven research institutes of the European Commission's Joint Research Centre (JRC). JRC-ITU was founded in 1963 on the site of the German nuclear research centre Karlsruhe. Most of its scientific activities today are dedicated to safety and security of the nuclear fuel cycle, basic actinide research as well as education and training. New sample preparation methods and safety performance of plutonium and minor actinide containing fuels have been investigated. Samples were prepared at JRC-ITU, have been irradiated in research reactors and returned to ITU for post-irradiation examinations. The tested fuel samples were based on metal alloys (e.g. MASURCA, METAPHIX), mixed oxides (e.g. SUPERFACT, TRABANT, OMICO, SPHERE, MARINE), nitrides and carbides (e.g. NIMPHE, NILOC, GOCAR, POMPEI), but also included Inert Matrix Fuels (IMF) for transmutation targets (e.g. EFTTRA-T4, ECRIX, CAMIX, COCHIX, HELIOS, FUTURIX). These irradiation campaigns have provided significant knowledge on safety performance and properties of solid fuels for various reactor systems. Current activities concentrate on safety research on fuels for existing power reactors and fuels for transmutation. Ongoing irradiation campaigns, SPHERE and MARINE, focus on safety aspects of mixed oxide transmutation fuels with significant americium content for homogeneous and heterogeneous fast reactor minor actinide recycling concepts.JRC.E.4-Nuclear Fuel Safet

UO2 corrosion by liquid sodium

International audienceIn some of the currently developed Sodium Fast Reactor (SFR) designs the core configuration will berearranged to include internal spent fuel storage positions, with the benefit of avoiding an externalsodium pool. However, in-vessel storage of failed fuel pins can lead to a direct contact betweencoolant and fuel, i.e. in a scenario where the cladding was breached, leading to their potential inter-action in case of oxide based fuel forms (UO2 and MOX). The reaction product of sodium and oxidefuel is generally denoted as Na3MO4 (where M=U, Pu), and characterized by unfavorable physical properties, which might result in fuel swelling and/or pulverization, with the consequence of fissileisotopes or fission products dissemination into the primary system. The understanding of the corro-sion mechanism and kinetics between liquid sodium and oxide based nuclear fuel becomes then ofprior importance for establishing the feasibility of an internal storage of failed fuel pins.In this contribution, we will present the results of out-of-pile tests that we perform to provide a basicknowledge of defective fuel pin behavior in contact with liquid sodium. With the aim to determinethe physical mechanism involved in the sodium-fuel reaction, we firstly focused on the behavior of UO2 corrosion by sodium.In order to cover the internal storage scenario, isothermal experiments were performed inside cap-sules with stagnant liquid sodium and UO2 at 800°C. To establish the influence of the grain orienta-tion on the growth process of the reaction product, well-oriented ( and ) single crystalswere used and finally to extend the behavior to the fuel pellet, a polycrystalline UO2 sample wastested as well. The corrosion product was analyzed by XRD, SEM-EDX and RAMAN. It consists ina homogeneous layer, whose morphology depends on the crystallographic orientation of the UO2 corroded grain or single crystal. However, the thickness of the corrosion layer does not seem todepend on the crystallographic orientation of the UO2 corroded grain that was unexpected.A tentative interpretation of UO2 corrosion by sodium is proposed. This interpretation will be usedfor further study on the modelling of MOX-sodium interaction. There the influence of Pu on the corrosion process will be addressed and added to the UO2-Na model