No abstract

Zirconium fuel claddings act as a first barrier against release of fission products during nuclear power plant operation and interim storage of the spent fuel. During the reactor operation, cladding tubes are exposed to different stress level at elevated temperatures and neutron irradiation in corrosive environment. It causes a material degradation by corrosion, cladding embrittlement by hydrides and radiationinduced damage or radiation growth and creep of the fuel rods. The irradiation damage effects mainly contribute to the loss of material ductility. In our study, microstructure of as-received (non-irradiated) Zr-alloys used in LWR (Zr1Nb, Zr-1Nb-1.2Sn-0.1Fe, Zr-1.5Sn-0.2Fe-0.1Cr) were examined by electron microscopy methods. Transmission electron microscope (TEM) was used to describe the microstructure of claddings used in different reactor conditions and identify the radiation-induced damage, which is presented on Zr1Nb irradiated to one standard campaign in the VVER-1000 active zone. Following Electron Backscatter Diffraction (EBSD) method on transparent foils complements the TEM results in larger area, i. e. by grain size and orientation or analysis of local misorientation after irradiation. Radiationinduced damage was observed in Zr1Nb metallic matrix as type dislocation loops, presence of radiation-induced precipitates or partial amorphization of the secondary phase particles. EBSD method showed no changes in crystallographic orientation, but a local increase of dislocation density can be affected by neutron irradiation.

Dosimetry of high doses of ionizing radiation is a method widely used not only in the field of basic and applied research but also in various industries. High-dose irradiation is used in the sterilization of foodstuffs and prolongation of their shelf life, sterilization of tools, materials and wastewater, treatment of antiquities attacked by woodworm organisms, biological and genetic research, inhibition of seed germination and retardation of fruit ripening. Furthermore, it has been applied in radiation resistance testing of materials, defectoscopy, industrial irradiation of materials (e.g. crosslinking and grafting of polymers or gemstone coloring by ionizing radiation), and last but not least, of course, nuclear energetics. In this work the dosimetric properties of polycarbonate are studied. They are compared with a standardized and certified method using alanine dosimeters. In the case of gammas the testing was realized for 60Co and neutron radiation was studied in the research nuclear reactor LVR-15.

No abstract

Materials under extreme conditions of radiation and temperature, as in nuclear facilities, need to be tested and analysed to understand the neutron-induced microstructural defects that might affect their mechanical properties at macroscale and thus affect the material performance. X-ray diffraction (XRD) is a widely use technique for structural characterization of materials in a bulk or powder form. Special care must be taken when manipulating radioactive material, especially in a powder form, since it can lead to unwanted radioactive contamination [1,2]. Therefore, the handling and milling of radioactive materials (e.g. minerals-rocks, concrete) is carried inside of a hermetically sealed shielded glovebox under negative pressure [3]. Milling in ethanol of the bulk material was performed using an oscillating ball mill, producing a fine powder (after air-drying) with an average particle size of 4 microns, "wet" milling offers the advantage to produce a powder with an homogeneous size distribution and also to avoid the dispersion of the radioactive dust into the air. Radioactive samples for XRD analysis must fulfil two requirements: 1) small size to avoid excessive irradiation, and 2) a contention barrier between the sample and its surroundings to avoid radioactive contamination due to leaking of powder. To meet those requirements a drop-casting of material (approx. 15 mg) onto PEEK foil (6 µm) has been chosen as a suitable option. After airdrying of the sample, it is covered with a second layer of foil and sealed with fast-drying glue to avoid powder leaking. The thus prepared sample is now ready for XRD analysis in transmission mode [4]. The data collection is performed using a multipurpose diffractometer (Empyrean from Malvern-PANalytical) with a Co X-ray tube, the diffractometer posses a magazine and a robotic arm for automatic loading of samples, besides it can be operated remotely reducing the exposition to radiation of the operator. With the described procedure phase identification, quantification of amorphous content using the internal-standard method, and monitoring of changes in lattice parameters of the identified crystalline phase can be safely performed on radioactive samples.One applicative example was the study of aggregates (majorly quartz, > 90 wt.%) under different levels of neutron fluences (up to 10 20 n/cm 2 ). Where it was observed a progressive amorphization of quartz from 9 wt.% to 76 wt.%, at the same time volumetric expansion of the unit cell was observed (up to 11%), as both axes a and c increased with the neutron fluence. Crystal density (g/cm 3 ), calculated from the previously calculated lattice parameters, decreases (-10%) with the increase of neutron fluence irradiation.In summary, the developed methodology represents an easy and affordable way to study the irradiated materials at laboratory scale.