Scientific Highlights NES
In the Nuclear Energy and Safety Research Division at PSI, Johannes Bertsch focuses on the so-called cladding tubes that are used in nuclear power plants.
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.
Spent fuel management is becoming one of the major concerns in many countries with a nuclear program. The radiation aspect as well as the safe and economical part of the long-term storage of the spent nuclear fuel has to be evaluated with a high degree of confidence. To assist such project from the neutronic simulation side, a new method is proposed to systematically calculate at the same time canister loading curves and radiation sources, based on the inventory information from an in-core fuel management system. The CS2M approach consists in coupling the CMSYS core simulation platform, developed over the year within the LRT/STARS to provide reference validated core simulation methodologies based on CASMO and SIMULATE, with the downstream state-of-the-art codes SNF and MCNP for decay- and criticality analyses respectively. In the present study, the considered cases cover enrichments from 1.9 to 5.0% for the UO2 assemblies and 4.8% for the MOX, with assembly burnup values from 7 to 74 MWd/kgU. Because it is based on the individual fuel assembly history, it opens the possibility to optimize canister loadings from the point-of-view of criticality, decay heat and emission sources. It also allows to perform a full uncertainty propagation at once: from the first irradiation to the entry in the storage facility.
Shortly after the Big Bang, radioactive Beryllium-7 atoms were formed, which today, throughout the universe, they have long since decayed. A sample of beryllium-7 artificially produced at PSI has now helped researchers to better understand the first minutes of the universe.
Reference: N. Leo et al, Nature Communications 9, 2850 (2018)
Read full article: here
Nuclear data for nuclear installations: Radiochemistry improves the precision of the cross-section data of long-lived radionuclidesMatter 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.
ETH Medal for outstanding MSc thesis: Beam Characterization of Low Energy Electrons from a Laser Wakefield Accelerator by N. SauerweinLarge 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
Global Sensitivity Analysis and Registration Strategy for Temperature Profiles of Reflood Experiment SimulationsNuclear Power Plant Safety
Global sensitivity analysis (GSA) is routinely applied in engineering to determine the sensitivity of a simulation output to the input parameters. Typically, GSA methods require the code output to be a scalar. In the context of thermal-hydraulic system code, however, simulation outputs are often not scalar but time-dependent (e.g. temperature profile). How to perform GSA on these outputs? A common solution is to represent the profile with a few selected scalar values and perform GSA on these scalar values. This is illustrated in the figure where stochastic samples of a temperature profile resulting from a quenching transient are obtained with the TRACE code in grey and where the maximum temperature and quenching time are chosen as scalars of interest. Their probability distributions, respectively shown in red and blue, can be used to perform GSA. However, these scalars might not be representative of the mixed variations in time and amplitude observed in the output of a typical transient. In this work we address the issue by studying two registration procedures – Landmark and Square Root Slope Function (SRSF) – which separate the amplitude and phase/time variations of the temperature profiles. We then perform dimension reduction by principal component analysis (PCA). PCA allows us to represent the variability of the phase-aligned time series in a few fixed eigenvectors representative of the transient physics and in their associated scalar eigenvalues, which are suitable for GSA. We compare the two registration procedures and the classical “scalar-of-interest” approaches using the Sobol’ indices sensitivity measure. This work received the best paper award at the Best Estimate Plus Uncertainty (BEPU) conference held in May 2018 in Lucca, Italy.
The Accident at the Fukushima Daiichi Nuclear Power Station, which occurred in March 2011, had a very strong impact on the nuclear community. Three reactors suffered core damage and fission products were released to the environment. Paul Scherrer Institute (PSI) has participated in an Organisation for Economic Cooperation and Development (OECD) project, Benchmark Study of the Accident at the Fukushima (BSAF). The project aimed to evaluate and analyse the accident progression, likely end-state of the reactor core after the accidents, and the release of radioactivity to the environment. PSI has concentrated on the analysis of unit 3 using MELCOR 2.1. Hundreds of calculations have been performed and a plausible scenario which predicted remarkably well the main signatures has been selected.
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.
Noise appears in many areas of science, and commonly has an unwanted and disturbing nature by deteriorating signals’ quality. Therefore, various techniques have been developed over the years for separating noise from pure signals. However, noise has a key role in signal analysis of nuclear reactors as its’ appropriate assessment can be used not only for exploring the normal and dynamic behaviour of nuclear cores, but also for identifying and detecting possible anomalies of reactor systems. State of the art methods have been recently implemented within the well-established signal analysis methodology of the STARS program, at the Laboratory for Reactor Physics and Thermal-Hydraulics (LRT), for investigating nuclear reactor noise and getting a better insight on analysing reactors’ operation.
Pt nanoparticles: The key to improved stress corrosion cracking mitigation in boiling water reactorsMaterials 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.
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.
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.
The Laboratory for Energy Systems Analysis at the Paul Scherrer Institute PSI is investigating how Switzerland’s electricity supply might look, up to the year 2050, under a variety of boundary conditions. On the basis of their calculations, the lab’s researchers are able to generate insights on possible future developments of the energy sector, for example, determine how an ambitious reduction in CO2 emissions could be achieved at the lowest possible cost.
Nuclear reactor dynamics deals with the transient behaviour of nuclear reactors which mostly refers to time changes of the imbalance between heat production and removal. Since the prediction of the dynamic behaviour is crucial for the safety of a reactor, computational models and methodologies have been developed in the framework of the STARS project, at the Laboratory for Reactor Physics and Thermal-Hydraulics (LRT), with the main goal to simulate the complex behaviours of reactors under various conditions with a high level of fidelity.
In most cases, electricity is generated when water is heated and transformed into vapour. Vapour bubbles in the water play a decisive role in this process. Using computer simulation, researchers at the Paul Scherrer Institute have succeeded in representing the behaviour of vapour bubbles – and in making their performance more calculable.
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.
At the Paul Scherrer Institute PSI, a small group of scientists is using theoretical models to explore an alternative for future nuclear reactors: so-called molten salt reactors. This helps to secure Switzerland’s expertise regarding globally relevant questions in the area of nuclear energy and reactor safety, for today and tomorrow.
Researcher at PSI (NES/LRT) have brought modern infrared technologies into their large thermal-hydraulic facility, called LINX, to obtain insights into condensation/evaporation process occurring under thermodynamic conditions resembling those of a nuclear power plant containment during a severe accident scenario. In such a scenario, condensation is of prime importance to control the thermodynamic state of the containment. It affects the pressure history, the overall gas (steam, hydrogen) and fission product distribution within this last barrier. Better understanding of these phenomena under accident conditions is essential to properly predict the accident evolution.
Post Irradiation Examination of MEGAPIE – How radiochemical analytics helps looking inside a high-power liquid metal spallation targetMatter 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.
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.
Researchers at the PSI have for the first time used a cyclotron to produce the radionuclide scandium-44 in a quantity and concentration as needed for medical treatment. With that, they have achieved the first precondition for scandium-44 to be used one day for medical tests in hospitals.
At the PSI, the Heavy Elements Research Group explores the exotic, unstable atoms at the end of the periodic table of elements. The dream: to discover one day the
island of stabilitythat could exist beyond the elements charted so far on the chemists' map.
22. February 2016Miscellaneous Energy and Environment Nuclear Power Plant Safety
Start of the public examination period for decommissioning of the nuclear facility Proteus at the Paul Scherrer Institute PSI
The nuclear research facility Proteus is a so-called zero-power reactor. In service, the thermal output of the reactor was limited to a maximum of 1 kW. That means this is an experimental reactor that was run at a power level so low that it did not require cooling. Proteus went into service in 1968. The PSI would like to decommission the facility. The decommissioning project is now being publicly announced in the legally prescribed, official publications.
8. February 2016Miscellaneous Energy and Environment Materials Research Nuclear Power Plant Safety
Start of the public examination period for renewed authorization to operate the research facility hotlab at the Paul Scherrer Institute PSI
The hotlab at the Paul Scherrer Institute PSI is a facility, unique in Switzerland, where researchers study highly radioactive materials in specially shielded chambers called
hot cells. It serves the needs of applied materials research on highly radioactive samples from core structural components and fuel rods from nuclear power plants, research reactors, and the PSI radiation facilities. Through its operation of the hotlab, the Paul Scherrer Institute also contributes to the safety of the nuclear power plants in Switzerland. Around thirty staff members attend to the hotlab's safety technology and analysis infrastructure.
4. December 2015Energie und Umwelt
Allen Warnungen vor den Folgen des Klimawandels zum Trotz und unbeeindruckt von politischen Absichtserklärungen: Die weltweiten Kohlendioxidemissionen steigen und steigen. Hauptverantwortlich dafür sind Kohle- und Gaskraftwerke, die den zunehmenden Strombedarf decken. Könnte man deren Kohlendioxidemissionen dauerhaft im Boden speichern, anstatt damit Atmosphäre und Klima zu belasten? Und wäre das auch für die Schweiz interessant? Diese Fragen beleuchtet der neueste Energie-Spiegel des PSI.
5. November 2015Media Releases Research Using Synchrotron Light Matter and Material
When bridges, dam walls and other structures made of concrete are streaked with dark cracks after a few decades, the culprit is the so-called the
concrete disease. Researchers from the Paul Scherrer Institute PSI and Empa have now solved the structure of the material produced in these cracks at atomic level - and have thereby discovered a previously unknown crystalline arrangement of the atoms.
8. October 2015Energy and Environment Nuclear Power Plant Safety
Microscopic deviations from the ideal structure render uranium dioxide, the fuel commonly used in nuclear power plants, more resistant to radiation damage.
30. July 2015Energy and Environment Environment
In a deep geological repository, low and intermediate level radioactive waste from nuclear applications is solidified by cementitious materials for several thousand years. Researchers from the Paul Scherrer Institute and the Karlsruhe Institute of Technology have now demonstrated how cement limits the mobility of those radioactive substances. The new findings improve our understanding of the processes involved in this early phase of deep geological disposal.
8. January 2015Energy and Environment
A study by the Centre for Technology Assessment TA-Swiss, coordinated by the Paul Scherrer Institute, recommends further pursuing deep geothermal energy in Switzerland. The energy resources underground are vast, environmentally friendly to extract and available around the clock, the authors conclude. The earthquake risk and the cost of electricity production, which are still too high, however, remain challenges that society needs to weigh up against the advantages of deep geothermal energy.
27. November 2014Energy and Environment Nuclear Power Plant Safety
These days, the Federal Office of Public Health distributes iodine tablets to the population living close to the Swiss nuclear power plants (NPP). The dispensing of iodine tablets within a radius of, now, fifty kilometres around NPP sites is aimed at protecting the residents from contamination with carcinogenic, radioactive iodine in the event of a severe nuclear accident.To make sure that as little radioactive iodine as possible gets into the environment as a result of a nuclear accident, researchers from the Paul Scherrer Institute PSI have for many years been developing a method that can be used in containment venting filters.
8. August 2014Energy and Environment
How susceptible is the global energy infrastructure to attacks by non-state actors? Has the number of attacks on this infrastructure actually increased of late? Which regions of the world are especially vulnerable? And which tactics do the attackers use? Scientists are looking to find the answers to these and other related questions with the aid of a database developed by researchers from the Center of Security Studies at ETH Zurich in collaboration with the Paul Scherrer Institute PSI.
14. July 2014Energy and Environment Nuclear Power Plant Safety
In nuclear reactors, water is dissociated at the surface of the hot fuel elements, thereby producing hydrogen. This hydrogen can penetrate the fuel cladding surrounding the actual fuel and weaken it mechanically. Researchers from the Paul Scherrer Institute (PSI) have been using neutrons and synchrotron radiation to study how the hydrogen gets into the cladding tube and what impact it can have once inside.
21. March 2014Energy and Environment Environment
Researchers from the Paul Scherrer Institute (PSI) and the Hungarian Academy of Sciences joined forces within an EU project to investigate the basic properties of argillaceous rocks in a repository for high-level radioactive waste. As the results reveal, the insights gained so far for Opalinus Clay can be transferred also to the Boda Clay found in Hungary.
7. March 2014Energy and Environment Environment
With ecoinvent, the Paul Scherrer Institute and its partners at ETH Zurich, ETH Lausanne, Empa and Agroscope have been running the world’s leading database for life cycle inventories for over ten years. The latest ecoinvent version 3 collects new data in areas such as electricity generation, agriculture, transport, mining and chemicals. In the power sector, which is significant for life cycle assessments, the database now covers over 80 per cent of the global production. And technology that has not been considered thus far such as enhanced geothermal systems is to be included in ecoinvent from now on. The result is more accurate ecological assessments of products and services
15. January 2014Energy and Environment Nuclear Power Plant Safety
Chemical reactions will change the nature of the deep repository and the surrounding rock (clay rock); that much is certain. But to what extent and with what impact on safety? Researchers from the Paul Scherrer Institute are looking to answer this question with the aid of a combination of experiments and computer simulations.
19. September 2013Energy and Environment Nuclear Power Plant Safety
Without computer simulations, the operation of nuclear power stations would be very difficult. Whether it is a question of installing new components or conducting safety tests, virtually everything has to be calculated and analysed on the computer first. At the Laboratory for Reactor Physics and Systems Behaviour of the Paul Scherrer Institute PSI, computational models and methodologies are developed with precisely this in mind. Through this, PSI researchers also act as an independent partner to the national regulatory authority ENSI and contribute thereby to support safe operation of the Swiss nuclear power plants.