Papers by Keyword: Neutron Irradiation

Abstract: Nitrogen-doped 6H-SiC single crystals irradiated with neutrons up to a fluence of 5.74×1018 n/cm2 at the temperature of 60-80°C were investigated by means of X-ray diffractometer and metallurgical microscope. The experimental results showed the X-ray diffraction peak (0006) was broadened due to the lattice distortion resulting from irradiation-induced defects, and then narrowed linearly when isochronally annealed over the temperature of 700°C. Meanwhile, from the chemical etching photomicrographs, the characteristic was accompanied by the changes of the dislocation density after the process of irradiation and post-irradiation annealing. According to this characteristic of irradiated 6H-SiC crystals, a novel temperature sensor suitable for the temperature range of 700-1300°C or more is developed, which depends on the linear relationship between XRD FWHM (the full width at the half maximum of X-ray diffraction peak) and isochronal annealing temperature over about 700°C. The subsequent application test demonstrated that the sensor remained no damage in the very harsh conditions as well as possessed a less than +5% of the relative temperature error. Therefore, the neutron-irradiated 6H-SiC can be employed as a kind of non-invasive temperature measurement sensor to determine the temperature of closed, high-speed rotating and difficult-to-access parts on a running machine such as internal-combustion engine pistons, turbine blades and so on.

Abstract: Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr precipitates in neutron irradiated Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 12 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. A saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC and the volume fraction of the Cr precipitates for neutron exposures above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. A specific surface tension of about 0.028 J/m² between the a matrix and the Cr-rich a' precipitate was found as best fit value for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS.

Abstract: The initial and deformed states of austenitic stainless steel AISI 321 before and after neutron irradiation with a damage dose up to 5.3 dpa at reactor core temperature of 350 °С were comparatively investigated. Corrosion behavior, mechanical properties are analyzed in the temperature range of 20…650 °С. It is shown that radiation damage of the steel in the deformed state significantly decreases in comparison with the initial coarse-grained state at the same level of corrosion resistance.

Abstract: We investigated mechanical properties of neutron irradiated Fe based binary alloys in order to extract roles of each alloying element in reactor pressure vessel (RPV) steels on irradiation hardening and annealing recovery behavior. Materials used were Pure-Fe, Fe-1Cr, Fe-1Mn, Fe-1Ni, Fe-1Cu and Fe-1Mo in at.%. Neutron irradiations were carried out at various irradiation doses from 0.3 to 8.5 × 1019 n/cm2 ( > 1.0 MeV) at 290 °C. Irradiation hardening of Fe-1Cu showed a tendency of saturation at a low dose. Irradiation hardening of Pure-Fe and the other binary alloys increased with increasing in irradiation dose. Especially, Fe-1Mn irradiated over 4.3 × 1019 n/cm2 showed significant irradiation hardening which is comparable to Fe-1Cu. However, the post-irradiation annealing recovery behavior of the irradiation hardening in Fe-Mn showed one-stage recovery at around 450 °C, which was completely different from the two-stages recovery behavior of Fe-1Cu.

Abstract: 9 – 12%Cr-MoVNb steels are successful materials for the use at higher temperatures. The universal application in turbines and power plants promises an expedient material for fission and future fusion reactors. Different developmental alloys were fabricated, irradiated and mechanically tested to optimize the material properties. Already, after the first irradiation tests could be shown that this type of steel has a reduced swelling and much faster decay of radioactivity than e.g. austenitic Cr-Ni-steels. This inherent property of reduced activation includes a high recycling potential. Further variations in the chemical compositions were carried out to increase the decay of radioactivity and to reduce the hardening and strengthening by neutron irradiation. The state of development today is a 9%Cr-WVTa-alloy, which is called EUROFER. The post-irradiation behavior and the development of material matrix are shown in comparison with further test alloys. The emphasis is to characterize the hardening mechanisms by irradiation at lower temperatures, which appear in helium bubbles, interstitial loops, and α`-precipitates.

Abstract: The free volume property and intermolecular interaction (especially hydrogen bonding) of poly (ether-urethane) (PEU) irradiated by neutron under different atmosphere has been studied by positron annihilation lifetime spectroscopy (PALS) and Fourier transform infrared (FTIR). The results suggested that the hydrogen-bonding interactions and free volume property in PEU depended strongly on the neutron irradiation dose.

Abstract: The coupling between copper rich precipitates (CRP) and point defects in neutron irradiated iron alloys and VVER steels was investigated by means of cluster dynamics (CD) simulations. The consideration of the strain energy effect on CRP kinetics as well as the application of the regular solution model for the case of different fixed copper contents of CRP provides a good agreement between the simulation results and experimental data for complex iron based alloys with small (0.015 wt%) and high (0.42 wt%) copper content. It was found that the CD simulation is applicable to irradiated VVER steel with 0.07 wt% of copper.

Abstract: Defect studies of neutron-irradiated Cr-Mo-V (VVER-440) type reactor pressure vessel steels were performed in the present work. The steels were irradiated in the nuclear power plant reactor under the conditions of a regular operation. Characterization of the irradiation induced defects was performed by two complementary techniques of positron annihilation spectroscopy: (i) positron lifetime spectroscopy was used for identification of defects and determination of defect densities, (ii) coincidence Doppler broadening was employed for investigation of Cu atom aggregates. Long range diffusion of Cu atoms is assisted by the irradiation induced vacancies. The solute Cu atoms form small clusters in the irradiated steels. Subsequent isochronal annealing of the irradiated steel leads to vacancy assisted clustering of Cu atoms and formation of small precipitates. The Cu clusters exhibit maximum diameter at 400oC. Above this temperature the clusters dissolve again in the matrix.

Abstract: Fast neutron irradiations on pre-treated Cz-grown silicon were carried out. The pretreatments involved thermal anneals at 450 oC and 650 oC under high hydrostatic pressure. We mainly examined, by means of IR spectroscopy, the effect of pre-treatments on the production of the oxygen-vacancy (VO) pair. The amplitude of the VO band was found independent on the 450 oC treatment although the amplitudes of the TDs bands were reduced. On the other hand, the amplitude of the VO band was found lower in the samples treated at 650 oC, indicating an influence on the production of the oxygen-vacancy defects. The results are discussed and explanations are suggested concerning possible interactions between thermal and radiation defects.

Abstract: Fast neutron irradiation of germanium has been used to study vacancy reactions and vacancy clustering in germanium as a model system to understand ion implantation and the vacancy reactions which are responsible for the apparently low n-type doping ceiling in implanted germanium. It is found that at low neutron doses (~1011cm-2) the damage produced is very similar to that resulting from electron or gamma irradiation whereas at higher doses (> 1013cm-2) the damage is similar to that resulting from ion implantation as observed in the region near the peak of a doping implant. Electrical measurements including CV profiling, spreading resistance, Deep- Level Transient-Spectroscopy and high resolution Laplace Deep-Level Transient-Spectroscopy have been used in conjunction with positron annihilation and annealing studies. In germanium most radiation and implantation defects are acceptor like and in n-type material the vacancy is negatively charged. In consequence the coulombic repulsion between two vacancies and between vacancies and other radiation-induced defects mitigates against the formation of complexes so that simple defects such as the vacancy donor pair predominate. However in the case of ion implantation and neutron irradiation it is postulated that localized high concentrations of acceptor like defects produce regions of type inversion in which the vacancy is neutral and can combine with itself or with other radiation induced acceptor like defects. In this paper the progression from simple damage to complex damage with increasing neutron dose is examined.