Scientific Highlights from Research Division Nuclear Energy and Safety (NES)

Scientific Highlights

18 February 2019

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Horizon 2020 project SAMOSAFER granted

The EU Horizon 2020 program granted 3.5 million Euros to the research and innovation project SAMOSAFER, where PSI is one of the 14 project partners. The total budget of the project, inclusive own and in-kind contributions, is 4.5 million Euros. The aim of SAMOSAFER project is to develop and demonstrate new safety barriers and a more controlled behaviour in severe accidents of the Molten Salt Reactor (MSR). Three groups at PSI will be involved in the project: the LSM groups for Advanced Nuclear Systems (ANS) and Multiscale Materials Modelling (MMM) and the Severe Accidents Research group (Sacre) of LRT, focusing on redistribution of the source term in the fuel treatment unit of MSR and assessment and reduction of radionuclide mobility during accidental conditions.

21 December 2018

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Time-Reversal Symmetry Breaking in Re-Based Superconductors

To trace the origin of time-reversal symmetry breaking (TRSB) in Re-based superconductors, we performed comparative muon-spin rotation and relaxation (μSR) studies of superconducting noncentro-symmetric Re0.82Nb0.18 (Tc=8.8 K) and centrosymmetric Re (Tc=2.7 K). In Re0.82Nb0.18, the low–temperature superfluid density and the electronic specific heat evidence a fully gapped superconducting state, whose enhanced gap magnitude and specific-heat discontinuity suggest a moderately strong electron- phonon coupling. In both Re0.82Nb0.18 and pure Re, the spontaneous magnetic fields revealed by zero-field μSR below Tc indicate time-reversal symmetry breaking and thus unconventional superconductivity. The concomitant occurrence of TRSB in centrosymmetric Re and noncentrosymmetric ReT (T=transition metal), yet its preservation in the isostructural noncentrosymmetric superconductors Mg10Ir19B16 and Nb0.5Os0.5, strongly suggests that the local electronic structure of Re is crucial for understanding the TRSB superconducting state in Re and ReT. We discuss the superconducting order parameter symmetries that are compatible with the experimental observations.

Reference: T. Shang et al., Physical Review Letters 121, 257002 (2018)

13 December 2018

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EPFL Adjunct Professorship to Christopher Mudry

Dr Christopher Mudry, who joined PSI in 1999 and is Research Group Leader of the Condensed Matter Theory Group at PSI since 2009, was awarded the title of Adjunct Professor at EPF Lausanne with the following citation. "Dr Christopher Mudry is a highly acclaimed theoretical physicist. He is regarded as one of the world’s leading experts on the quantum field theory of condensed matter and in the rapidly developing field of the topological properties of matter."

3 December 2018

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Progress in non intrusive laser based measurements of gas-phase thermoscalars and supporting modeling near catalytically reacting interfaces

Heterogeneous and combined hetero/homogeneous chemical processes have attracted increased attention in many energy conversion systems, which include large scale power generation, microreactors for portable power generation, household burners, fuel processing technologies and automotive exhaust gas aftertreatment. Progress in such systems crucially depends on the development of catalysts with enhanced activity and thermal stability and on the comprehensive understanding of the fundamental processes occurring near gas solid reacting interfaces. Recent advances in non intrusive lased based measurements of gas phase thermoscalars over the catalyst boundary layer are reviewed. Such measurements, combined with theoretical analyses and numerical simulations, have fostered fundamental investigations of the catalytic and gas phase chemical processes and their coupling at industrially relevant operating conditions. The methodology for assessing local catalytic reaction rates and validating gas phase reaction mechanisms under steady conditions using 1D Raman and planar laser induced fluorescence (PLIF) of radical species, respectively, is presented first. Progress in the measurement of minor and major stable species using PLIF is outlined and the potential of this technique as a suitable method for assessing the catalytic reactivity under dynamic operating conditions is discussed. State of the art numerical modeling necessary for the interpretation of the measurements is presented in parallel with the laser based techniques. Turbulence modeling, direct numerical simulation (DNS) and near wall non intrusive measurements of species concentrations and velocity have clarified aspects of the complex interplay between interphase turbulent transport and hetero /homogeneous kinetics. Controlling parameters are the competition between the heterogeneous and homogeneous reaction pathways, diffusional imbalance of the deficient reactant, flow laminarization induced by the hot catalytic walls, and fuel leakage through the gaseous reaction zone that leads to concurrent catalytic and gas phase combustion. Experimental needs for assessing turbulent fluctuations of catalytic reaction rates as well as for investigating intrinsic instabilities (heterogeneously or homogeneously driven) are discussed. Future directions for combining in situ surface science diagnostics with in situ non intrusive gas phase thermoscalar diagnostics and for advancing current numerical tools are finally proposed.

4 June 2018


Nuclear data for nuclear installations: Radiochemistry improves the precision of the cross-section data of long-lived radionuclides

Matter and Material

Knowledge about the cross sections data of the target materials used for spallation neutron facilities (SNF) and accelerator driven systems (ADS) is essential for the licensing, safe operation and decommissioning of these facilities. In addition, these data are important to evaluate and improve the existing computer simulation codes. Especially the α-emitter 148Gd has a large contribution to radio-toxicity of spallation target facilities with its 74.6 years of half-life. As the laboratory of radiochemistry, we used radiochemical methods to improve the precision of the production cross section data of long-lived radionuclides from proton irradiated lead, tantalum and tungsten targets. These results are long awaited in the nuclear data community and are of paramount importance for the evaluation of the theoretical codes. They will have a high impact on the design of high-power spallation neutron facilities, in particular the ADS prototype MYRRHA and the European Spallation Source, which is going to be the world`s most powerful neutron source. Our work has recently been published in the internationally high ranking journal Analytical Chemistry.

24 May 2018


ETH Medal for outstanding MSc thesis: Beam Characterization of Low Energy Electrons from a Laser Wakefield Accelerator by N. Sauerwein

Large Research Facilities

The characteristics of low energy electrons accelerated by a laser wakefield (Laser Wakefield Acceleration LWFA) has been studied. The work included understanding the acceleration process, setting up the experiment and measuring properties like charge, divergence and energy of the accelerated electrons. The experiment included diagnostics for the laser and the electrons. In order to make high-resolution energy distribution measurements with relative errors ∆E/E of below 10%, a tunable electron spectrometer has been designed, built and characterized. A tunable permanent magnet quadrupole triplet has been designed for stigmatic focusing in a range of 5 keV to 5 MeV. The thesis can be found here: MSc Thesis N. Sauerwein

24 January 2018


Neutron radiography of detrimental hydrogen in nuclear fuel claddings

Materials Research Energy and Environment Nuclear Power Plant Safety

Hydrogen is at the source of degradation mechanisms affecting mechanical properties of many structural metal materials. In nuclear power plants, zirconium alloy fuel cladding tubes take up a part of the hydrogen from coolant water due to oxidation. Because of the high mobility of hydrogen interstitial atoms down temperature and concentration gradients and up stress gradients, hydrogen distribution in fuel claddings can often be non-uniform, arising the risk for the integrity of spent fuel rods under mechanical load. At the Laboratory of Nuclear Materials (LNM) in collaboration with the Laboratory of Neutron Scattering and Imaging (LNS), hydrogen redistribution in zirconium alloys was quantified by neutron radiography using the state-of-the-art detector of PSI Neutron Microscope, and the concentration was computed based on thermodynamics, to predict hydrogen diffusion and precipitation for used nuclear fuel.

3 October 2017


Pt nanoparticles: The key to improved stress corrosion cracking mitigation in boiling water reactors

Materials Research Energy and Environment Nuclear Power Plant Safety

The formation and growth of cracks by stress corrosion cracking (SCC)in reactor internals and recirculation pipes due to the highly oxidising environment is a serious issue in boiling water reactors. At first, SCC mitigation was attempted by injecting H2 into the feed water, where the injected H2 recombines with the H2O2 and O2 to water and reduces the electrochemical corrosion potential, and consequently the SCC susceptibility. Several disadvantages of the injection of high amounts of H2, have led to the development of noble metal additions to the reactor feed water. With injection of a much smaller amount of H2, the noble metal particles of a few nanometres in size, formed in-situ, work as catalysts for the efficient reduction of the oxidizing species formed by radiolysis, and thus lower the ECP and SCC susceptibility.

15 September 2017

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Sorption of trivalent lanthanides and actinides onto montmorillonite

Materials Research Energy and Environment

The credibility of long-term safety assessments of radioactive waste repositories may be greatly enhanced by a molecular level understanding of the sorption processes onto individual minerals present in the near- and far-fields. A study conducted at LES in collaboration with the Helmholtz Zentrum Dresden Rossendorf used extended X-ray absorption fine structure (EXAFS) and time-resolved laser fluorescence spectroscopies (TRLFS) to elucidate the uptake mechanism of trivalent lanthanides and actinides (Ln/AnIII) by the clay mineral montmorillonite.The excellent agreement between the thermodynamic model parameters obtained by fitting the macroscopic data, and the spectroscopically identified mechanisms, demonstrates the mature state of the 2SPNE SC/CE sorption model developed at LES for predicting and quantifying the retention of Ln/AnIII elements by montmorillonite-rich clay rocks.

19 April 2017

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BKW and PSI agree on partnership for safety analysis services

Nuclear Power Plant Safety

BKW’s Engineering Division and the Paul Scherrer Institute (PSI) joined forces to provide risk and safety analysis services in the nuclear sector. By combining their expertise, the two companies are able to solve highly complex problems in the field of nuclear safety. The range of joint services is aimed at customers from the power plant sector and supply industry, as well as public and state institutions. The collaboration will focus exclusively on the international (non-Swiss) market.

19 October 2016


Radioactive targets produced at PSI enable improving the Big Bang Theory

Matter and Material

One of the long-lasting unsolved problems in Nuclear Astrophysics is the so-called "Cosmological Li Problem", i.e. the large discrepancy between the primordial 7Li abundance predicted by models of Big Bang Nucleosynthesis and the one inferred from astronomical observation. The study of the production/destruction rates of the radioactive precursor 7Be is one of the clues for solving this problem. Scientists from PSI were able to manufacture two highly radioactive 7Be-targets for the measurement of the 7Be(n,α) cross section at n_TOF CERN. The activity was extracted from the cooling water of the neutron spallation source SINQ. As a result of the experiment, the investigated reaction could be ruled out as responsible for the problem. The innovative work on isotope and target production as well as the new measurement techniques specifically developed for this kind of experiments make further investigations on this "hot topic" feasible. The work has been published in Physical Review Letters and has been selected for the Editor’s Suggestion of the corresponding issue.

14 September 2016

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Post Irradiation Examination of MEGAPIE – How radiochemical analytics helps looking inside a high-power liquid metal spallation target

Matter and Material

PSI radiochemists now finished the radiochemical analysis of the residue nuclei production in the Lead-Bismuth Eutectic (LBE) of the MEGAPIE target. Twenty – mostly safety-relevant – radionuclides could be identified and quantified. Comparisons with theoretical predictions show acceptable agreement in most cases, but also considerable discrepancies for some selected radionuclides. Moreover, the scientists learned that noble elements like Gold, Silver, Mercury or Rhodium are homogeneously distributed in the bulk LBE, while others, sensitive to reduction/oxidation (Lanthanides, Iodine, Chlorine), tend to accumulate at exposed positions like vessel walls and free surfaces. These results will help to improve models and codes for predictions and, thus, will improve the safety of existing and future facilities.

26 August 2016

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The chemical state of 79Se in spent nuclear fuel

Materials Research Energy and Environment Nuclear Power Plant Safety

An interdisciplinary study conducted at different PSI laboratories (LES, AHL, LRS, SYN) in collaboration with Studsvik AB (Sweden) demonstrates that selenium originating from fission in light water reactors is tightly bound in the crystal lattice of UO2. This finding has positive consequences for the safety assessment of high-level radioactive waste repository planned in Switzerland, as it implies (contrary to previous assumptions) that the safety-relevant radionuclide 79Se will be released at extremely low rates during aqueous corrosion of the waste in a deep-seated repository.