Ujp Praha (Czechia)

Despite decades of advancements and research aimed at improving fuel’s physical properties, fretting damage to fuel cladding remains a significant challenge. This study outlines the findings of experiments conducted on Zr-1%Nb alloy coated with protective layers composed of chromium-aluminium (CrAl) compounds and other new perspective materials, such as FeCrAl and CrNi alloys, at the Research Centre Řež. The experiments included debris-fretting tests performed under LWR conditions (320 °C and 15 MPa) and microscopic evaluations of groove depths. The primary goals were: (1) to evaluate the debris-fretting resistance of uncoated Zr-1%Nb samples compared to Zr-1%Nb with coatings and new alloys, and (2) to investigate the potential effects of coatings and new materials on the durability of fuel cladding. The conducted experiments and studies confirmed the benefits of the wear resistance of the ATF types of claddings in comparison to the standard Zr-1%Nb cladding material. Various parameters, such as wire wear and the influence of mutual position of the samples, were considered during the testing to provide the most precise insight into the wear resistance of the tested samples.

New energy generation methods are currently being discussed with a view towards the transition from traditional primary sources to more environmentally friendly options, particularly renewables. Energy storage is also closely related to this transition. Battery storage currently dominates this area. However, flywheel energy storage system technology offers an alternative that transforms stored kinetic energy into mechanical and electrical energy using a motor generator. The flywheel energy storage system technology is thus flexible and can be applied in different industrial applications. The management of the technology of recycling tungsten multi-metallic composites (W-MMC) waste material from other products and the subsequent trial production of high-strength W-MMC material with a density of more than 17,500 kg/m3 from recycled powders allowed us to test the limits of the so-called “heavy” flywheels used in rotor production. The results achieved lead to the conclusion that the developed recycled materials of the W-MMC type with a density ≥17,500 kg/m3, with a yield strength of 1200–1700 MPa depending on the production method, can be used as a substitute for the structural steels used today without an enforced reduction in the maximum allowed rotor speed due to exceeding the maximum allowed stress.

The present study focuses on the evaluation of the mechanical properties degradation of Cr-coated Zr-alloy fuel cladding. The main objective of the work is to find a suitable methodology to evaluate the mechanical properties degradation of coated cladding by performing several separate effects experiments.Apart from the many positive effects of protective coatings on the overall cladding properties, coatings’ general disadvantage is their reduced ability to tolerate plastic strain. Therefore, coating cracks might occur in the first stage of the hypothetical Loss of Coolant Accident (LOCA). The study is unique because of the consideration of coating cracks. Prior to the high-temperature (HT) oxidation, samples were subjected to either a scratch test or burst test, resulting in the creation of coating defects. The subsequent evaluation of the obtained data consisted of wavelength dispersion spectroscopy (WDS) and optical microscopy analysis and hydrogen content measurements.

Abstract The fretting phenomenon was responsible for over 50% of fuel failure cases in the years 2010–2015 according to International Atomic Energy Agency (IAEA). It shows the scale of the problem for the nuclear power generation sector. A big share of this issue is related to debris fretting. Although debris fretting has been studied for decades, the available R&D information is scarce. The presented paper summarizes the work performed in the Research Center Řež (CVŘ) on Zr–1%Nb alloy tube specimens covered with protective coatings—passivation oxide layer and pure chromium layer. The tests included the simulation of debris-fretting conditions and detailed analysis using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and focused ion beam (FIB). Those experiments are a part of a wider project devoted to the research in the specification of the fretting wear increase after applying the protective layer. The first outputs show the positive impact even in the case of an oxide layer's presence on the cladding surface.

The properties of positrons delocalized in the HfNbTaTiZr complex concentrated alloy are investigated theoretically and related to available experimental data. Positron lifetimes calculated for random atomic arrangements appear to be short compared to the experiment carried out on a vacancy-free sample. Contrarily, a configuration exhibiting a local atomic order provides a lifetime that is very close to the experimental value. These observations indicate that the local atomic order is occurring in the studied alloy, in agreement with other measurements. The analysis of calculated results shows that the positron lifetime and affinity are affected to some extent by the alloy substitutional disorder, lattice relaxations, and charge transfer among atomic species, which should be taken into account in precise calculations.

Refractory high entropy alloys (HEA) are promising materials for high temperature applications. This work presents investigations of the room temperature tensile mechanical properties of selected 3 and 4 elements medium entropy alloys (MEA) derived from the HfNbTaTiZr system. Tensile testing was combined with fractographic and microstructure analysis, using scanning electron microscope (SEM), wavelength dispersive spectroscope (WDS) and X-Ray powder diffraction (XRD). The 5 element HEA alloy HfNbTaTiZr exhibits the best combination of strength and elongation while 4 and 3 element MEAs have lower strength. Some of them are ductile, some of them brittle, depending on microstructure. Simultaneous presence of Ta and Zr in the alloy resulted in a significant reduction of ductility caused by reduction of the BCC phase content. Precipitation of Ta rich particles on grain boundaries reduces further the maximum elongation to failure down to zero values.