Добірка наукової літератури з теми "Ni-60Co alloys"

This study investigated the influence of 60Co-γ-irradiation on the structure and properties of Cu-Al-Ni shape memory alloys. The phase transformation temperatures were evaluated by differential scanning calorimeter (DSC). It was found that the γ-irradiation had a complex influence on the phase transformation parameters of Cu-Al-Ni SMAs. However, the transformation temperatures were shifted and a new curve was obtained after exposure to different irradiation doses. The thermodynamic parameters such as enthalpy and entropy tended to increase/decrease depending on the amount of the exposure. The structural properties of the exposed samples were studied by using optical microscopy and hardness measurements at room temperature. It was also found that the structural-properties of the Cu-Al-Ni SMAs were completely affected by the amount of the applied γ-irradiation dose.

Tracer diffusion of 60Co and 63Ni in the amorphous alloy NiZr near the equiatomic composition has been measured in the temperature range between 486 and 641 K using the ion-beam sputter-sectioning technique for serial sectioning. The temperature dependence for the diffusivities of Co and Ni in a-NiZr exhibit Arrhenius behavior; these can be expressed as follows: D∗co = 3.6 × 10−7 exp [− (135 ± 14) kJ mol−1 /RT] m2/s and D∗Ni = 1.7 × 10−7 exp [− (140 ± 9) kJ mol−1 /RT] m2/s. The values of D∗Ni are in good agreement with those measured by the Rutherford backscattering technique. The measured diffusivities were independent of time, indicating that no relaxation took place during diffusion.

In the nuclear field, efforts are made to find substitutes to cobalt hardfacing alloys since these alloys have a principal drawback, the transmutation from stable 59Co to 60Co under neutron irradiation. In case of wear, fragments could be deposed on the surface of primary circuit and thus contaminate it, causing a real issue for deconstruction.

ABSTRACTOn April 25, 1986, the nuclear reactor Unit 4 (RBMK) at Chernobyl, Ukraine, exploded. Besides molecular species, the fallout contained particles of relatively high specific activity (hot particles) with a wide range of chemical compositions. The composition of a hot particle bears information about its genesis. Particle sizes ranged from a few to 100s of micrometers. Data on a hot particle, found in Berlin, Germany, is presented and discussed in context with earlier measurements on other particles to understand their genesis. The chemical composition was determined by electron probe micro analysis. Our particles are either reactor fuel (one) or fission product alloys (nine). The alloys were formed during normal reactor operation. Strongly varying concentrations of Fe and Ni suggest that at least some of our particles reacted with molten structural material of the reactor. The particles were mobilized by fuel oxidation or fuel dust generation during the accident. The fission product composition can only be explained if we assume that the alloys remained in the solid state in the course of the accident. Some particles may have been ejected during the explosion, others later while the reactor was burning. Activities (103Ru and 106Ru, originally up to 160,000 Bq) of our ten year old particles were re-measured but were no longer detectable. No long-lived γ-emitters were found. The 99Tc activity was calculated and found to only lBq. The γ -spectrum of the fuel particle still shows 137Cs (1 Bq) and 60Co (<1 Bq).

The phenomenon of recrystallization and corresponding texture evolution in metallic systems has been studied for several decades yet not understood completely. The complexity of the problem arises due to its dependence on several factors such as crystal structure, the composition of material, stacking fault energy, deformation texture, pre-deformation parameters, annealing parameters, etc. Hence, a systematic study on the evolution of recrystallization texture considering the effect of all these factors is highly desirable. In the present study, a close examination reveals that most of these factors are interrelated. Moreover, microstructural features and texture prior to recrystallization play a significant role in deciding the evolution of recrystallization microstructure and texture. These two factors are directly related to the stacking fault energy of the material. Hence a study elucidating the role of stacking fault energy on the development of texture would encompass the mechanisms of evolution of recrystallization texture. In the present investigation, two types of alloy systems have been investigated: the Ni-Fe alloy system, where alloying addition does not affect stacking fault energy, and the Ni-Co alloy system, where alloying addition leads to systematic variation in stacking fault energy. After recrystallization, the Ni-Fe alloys show non-uniform α-fiber recrystallization texture. In the case of Ni-Fe, the addition of alloying leads to some fine differences in the recrystallization texture, which has been attributed to the highly heterogeneous deformed microstructure resulting after alloying. The Ni-Co alloys also show non-uniform α-fiber recrystallization texture with the exception of Ni-20Co, and Ni-60Co alloys, where a relatively uniform α-fiber recrystallization texture evolves. It is attributed to the inherent heterogeneity of the as-deformed microstructures. In all the cases, the entire recrystallization stage is dominated by the formation of the annealing twin (Σ3) boundary. The mechanism of evolution of recrystallization texture in each case and the role of different deformation feature during recrystallization has been investigated in detail. The cellular automata simulation technique has been used to simulate the different phenomena during the recrystallization process. The evolution of recrystallization microstructure, texture, kinetics, and grain size distribution has been simulated.

This research evaluated the applicability of chlorination reaction treatment as processing technology to recover Zr metal which becomes reusable resources from radioactive Zr metal wastes. The typical waste generates from reprocessing facilities, and the main component of waste is a zirconium alloy containing 90–95% of Zr. At first, the volatility of ZrCl4 produced by the chlorination reaction of Zircaloy-2 was theoretically calculated with thermodynamic simulation code. The estimation showed that Zr could be effectively separated and recovered from this alloy by the difference of volatility in each element chloride. The chlorination reaction of metal proceeds as an exothermic reaction and the control of the reaction temperature is an important condition in order to perform optimal Zr separation recovery. The chlorination reaction of Zircaloy-2 was carried out in the low-temperature ranges of 220°C–320°C, and Zr separation performance was experimentally obtained. Zr and Sn (1.5wt% content in Zircaloy-2) volatilize 100% as chlorides at 270°C or higher temperature. The amounts of volatilization of Cr and Ni are 5% and 0.1% or less, respectively. Such volatile ability is well in agreement with the result of thermodynamic calculation quantitatively. The volatile behavior of Fe (0.2wt% or less content) in Zircaloy-2 is influenced by the product of FeCl2 which is due to the heat decomposition of FeCl3 with larger volatility, and the experimental volatility is smaller than the theoretical one. 60Co produced in the radioactivated Co by neutron radiation is a highest radioactivity source in the hull waste and it should be completely separated and removed from the recovered Zr chloride. In this study, the metal powder of Co was used to measure the volatility, because the content of Co in Zircaloy-2 is very small quantity (20 ppm or less), The obtained volatility was a hundredth of the volatility of thermodynamics calculation. U and Cs also intermingle in the hull wastes by the solid solution or the adhesion of uranium fuel. The volatility of Cs and U in the chlorination reaction at 270°C was measured by using CsCl, and UO2 in the coexistence of Zircaloy-2. The volatility of UO2 and CsCl was 4times and thousand times higher than that without the alloy, respectively. The exothermic reaction in the chlorination of metal was inferred. However, the volatility did not influence the effective ability of decontamination for the recovered Zr chloride. In order to recover the high-level decontaminated Zr chloride from radioactive nuclides, it is necessary to efficiently remove radioactive nuclides, which are the sources of high radioactivity due to 60Co, 63Ni and 137Cs. It was evaluated that a chemical addition treatment in which the amounts of radioactive nuclides relatively decreases by the amounts of radioactive nuclides relatively decreases by the amount of added stable isotopes of chemical compound was a effective treatment, on basis of the calculation of volatility of each element. The addition treatment of chemical compound performs in the distillation of Zr chloride obtained by the chlorination of hull waste. This study showed that a basic process of the high-level decontaminated Zr recovery consists of the two-step process of both chlorination reaction of the hull waste and distillation treatment of Zr chloride in addition of chemical compound.