JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2017 | Volume:- | Issue:79 |Papers Count:11

Nowadays, high temperature superconductor magnet applications have become a reality due to increases in conductor performance. Detailed knowledge of the superconducting to resistivity transition (quench) process is essential and usually this transition is described by power law. In this paper, the quench and the process of quench propagation are studied in a short sample of Bi-2223/Ag superconducting tape by applying localized heat pulses and using 1D simulation with the Comsol multiphysics 4. 4 program. The minimum quench energy (MQE) and quench propagation velocity (vMPZ) are two important parameters for the stability and protection of a superconducting magnet. Hear, by increasing the current and temperature, the MQE decreasing rate is investigated as a superconducting stability factor. Moreover, the changing rate of the normal zone propagation velocity is studied as a self-protection parameter against the quenching.

Image prosseing methods is useful for extraction of the defects such as porosity, slag and crack in the noisy and low contrast industrial radiography images. It is noticeable that the defects appear as the gradients in pixel values, therefore, the gradient based method can help to detect the defects. In this research, different methods of gradient extraction such as Soble, Perwitt and the nonlinear diffusion filter were implemented and tried to improve the edges and the defect detection. The nonlinear diffusion filter method depends on diffusion coefficient, k, and the chosen value for k can affect the exact smoothing of the edges. Thus, in this attempt, by the use of a new approach, in comparison with the conventional edge finder methods, a nonlinear diffusion filter method is repeated and the edges are smoothed in the obtained images. Then, the defects in the gradient of images are extracted by substracting the original image from the obtained image. The mentioned methods were implemented in different radiography images. The results show that the proposed method in comparison with local gradient ones such as Sobel and Perwitt methods has superiority over different radiographic images as confirmed by the radiography film interpreters.

In this paper, uncertainty and sensitivity of emergency cooling systems of the primary and secondary circuits are investigated in the VVER1000/V446 nuclear reactor during the small break (SB)-LOCA. The emergency systems include accumulators, high pressure and low pressure injection systems and emergency feed-water system. The analysis is performed using the RELAP5/Mod 3. 2 Code for nodalization and simulation of the nuclear power plant. The GRS method is used for the calculation of the minimum number of the code to achieve 95% of the tolerance limit and confidence level. For a conservative analysis of the accident, the loss of power to the NPP and the failure of the two diesel generators are considered when SB-LOCA occurs. These limitations cause the malfunctioning of the two channels of the emergency cooling systems. Also, by considering the single failure criteria, one accumulator is failed throughout the accident process. The results show that the accumulators deuelop the most sensitivity of the maximum clad temperature. Also, the HPIS pumps have relatively little influence on the SB-LOCA. When all emergency cooling setpoints are altered, a new set is achieved, which causes to lower the maximum clad temperature, in comparison with a default setpoint of the emergency cooling systems.

Extracts of two varieties of barberry including Berberis integerrima and Berberis vulgaris were prepared by water as a solvent, in darkness, with a pH=3 and at a temperature of 25˚ C. Then the effects of gamma radiation processing with doses of 0. 5, 1, 2. 5, 5, 7. 5 and 10 kGy were studied on the profile and concentration of organic acids and water soluble vitamins. By a high-performance liquid chromatography (HPLC) in the control samples oxalic, tartaric, quinic, malic, ascorbic, shikimik, malonic, acetic, maleic, succinic and fumaric acids and C, B5, B6, B1, folic acid, biotin and B2 vitamins were identified. In the Berberis integerrima acetic, ascorbic and malonic acids and biotin, folic acid and thiamin vitamins; and in the Berberis vulgaris malic, ascorbic and malonic acids and B1, biotin and B5 vitamins were dominant. In both cultivars fumaric acid, in the Berberis integerrima B2; and in the Berberis vulgaris folic acid had the least amounts. After the gamma processing in the Berberis integerrima, Malic (10 kGy), acetic (0. 5 kGy) and ascorbic (10 kGy) acids and B5, biotin and B1 (0. 5 kGy) vitamins; and in the Berberis vulgaris acetic (0. 5 kGy), succinic (2. 5 kGy) and malic (7. 5 kGy) acids and B5 (10 kGy), B1 (1 kGy) and biotin (10 kGy) vitamins were the most.

The use of nanofluids to increase the safety margin of high heat flux thermal systems in nuclear power plants through the enhancement of the critical heat flux (CHF) has been considered recently by researchers. To investigate the CHF characteristics of nanofluids, pool boiling experiments of nanofluids with various concentrations of TiO2, Al2O3 and SiO2 nanoparticles were carried out using a 0. 2 mm diameter cylindrical Ni– Cr wire under the atmospheric pressure. The results showed that the CHF of SiO2 nanofluid is significantly enhanced by 56% compared with that of pure water by increasing the nanoparticle concentration to 0. 05 wt%. Microscopic images, subsequent to the CHF experiment of SiO2 nanofluid, revealed that nanoparticles are deposited on the wire surface during the pool boiling of the nanofluid. The CHF of pure water was measured on a nanoparticle-coated wire which was produced during the pool boiling experiments of SiO2 nanofluids. The results of these experiments showed clearly that the main reason for the CHF enhancement of the nanofluid is the modification of the heating surface by the SiO2 nanoparticle deposition during the pool boiling.

Combination of carbon nanotubes with polymers in an especial weight percentage called electrical percolation threshold, leads to a sudden increase of several orders of magnitude of the electrical conductivity of the polymer-carbon nanotube composite. In the present research, considering these characteristics, the idea of using Polymethyl Methacrylate-Carbon Nanotube composite as an active dosimeter is exhibited. One of the factors affecting the response of this type of dosimeter is the variation of electrical resistance in the composite due to absorption of radiation. For investigation of dosimetric parameters of this composite in different dose rates, the COMSOL software and finite element method were utilized. In this simulation, the electrical current density of PMMA-CNT composite with a thickness of 10μ m under a constant voltage of 3 V in different dose rates for 2 min was calculated for the samples having different weight percentages of carbon nanotubes adjacent to the electrical percolation threshold region, namely 0. 17, 0. 19 and 0. 30. The value of the absorbed dose was calculated through the product of the dose rate by the irradiation time. Linearity of the dose response in the range of 400 mGy to ~3 Gy in the diagnostic and therapeutic dose levels could be considered as a positive factor for dosimetry applications of this composite material.

The nanolayered ternary compound Ti3SiC2 is a representative of those materials that exhibit the characteristics of both metals and ceramics. Similar to metals, Ti3SiC2 shows high electrical and thermal conductivity, high thermal shock resistance, ductility and good machinability. Further, similar to a ceramic, Ti3SiC2 has a high Young’ s modulus, as well as, high temperature strength and oxidation resistance. In this paper, T3SiC2 bulks have been synthesized by infiltrating Si liquid into a porous preform composed of solid TiC powders. Silicon pellets were placed on the top of the precursor pellets as the liquid source. The starting compositions can be represented by the formula 3TiC/1. 3Si. The phase formation and microstructure were investigated by the X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with an energydispersive spectroscopy (EDS) system. The results demonstrated that the TiC preform could react with Si in order to MAX phase synthesis and SiC impurities appeared in the cross section of the samples. It is found that the compositions of the samples strongly depended on the time of infiltration. Moreover, an increase in the time, decomposed Ti3SiC2 into TiC compound.

Nanofiltration is a novel membrane technology that can be used in different industries such as nuclear fuel cycle for components separation from solutions. So, the objective of this research is the selection and investigation of the effect of main process parameter on the nanofiltration membrane process for uranium ions separation from the aqueous solution. The significance and effectiveness of pH, pressure, feed flux, feed concentration, and concentration of carbonate as a complexation agent were investigated by the MINITAB software. The results indicated that pH is the main parameter affecting the nanofiltration process. The effect of pH on the process performance was investigated. The results showed that by increasing pH from 3 to 9 leads to an increase in the permeate flux from 42. 47 to 80. 58 l/(h. m2). Also, the rejection coefficient increased from 10 to 98. 58%. The high separation obtained for uranium ions shows that nanofiltration process has a good potential for the uranium separation and recovery from the aqueous solution.

137Cs is one of the products of nuclear fission. Due to its energetic gamma-ray emission along with the decay and long half-life, it is one of the most important environmental radionuclides. Transfer of radionuclides from air, soil and freshwater to the foodchain of the mankind will endanger the human health. Potassium, as an essential macronutrient for plants due to the similarity of its hydrated radius to that of the caesium, has the similar behavior in soil and plant. So, in this study, the relationship between caesium and potassium in soil and plant and the ability of caesium uptake was investigated. A pot experiment in a factorial design, based on randomized complete block, was performed with two plant species; Dent corn (Zea mays L. var. indentata), Akbari potato (Solanum Tuberosum), 3 levels of 133Cs (0, 17 and 34 mgkg-1 of soil from caesium nitrate) and 3 levels of potassium (0, 22. 5 and 45 mgkg-1 of soil from potassium sulfate), containing 6kg soil per pot with three repeats. The results showed that the effects of the plant species, caesium and potassium treatments are significant (P<0. 01). The average amount of caesium in corn and potato were, respectively, 29. 55 and 9. 15 mgkg-1 dry matter. By increasing the amount of caesium to 17 and 34 mgkg-1 of soil, increased the plant's absorption of caesium by 227% and 537%, respectively, compared with the controlled one. The interaction effect of caesium and potassium treatments in the amount of caesium of the plant was significant (P<0. 01). The results showed that the increase of the potassium in excess of the plantsʼ need in 22. 5 and 45 mgkg-1 of soil, the treatment of potassium has reduced the caesium uptake by 53% and 37%, respectively, compared with the controlled one.

To evaluate the effect of laser irradiation on the salinity tolerance in barley (hordeum vulgare L. ) in the germination phase and seedling, a three-replicate experiment with CRD in a factorial arrangement experimental type has been previously conducted in Iran. Experimental factors were four barley genotypes (Reihan, Afzal, Fajr30 and Nosrat), two radiation levels (no laser and laser irradiation at 780 nm wavelength for 15 minutes) and five levels of salinity (0, 80, 160, 240 and 320 mM of sodium chloride). In this research, in the germination parameters (root length, shoot length, coleoptile length, root number, germination percentage, mean germination time, dry weight of seedling, seed vigor, and germination rate), all genotypes were significantly affected by increasing the salinity and laser irradiation (P<0. 01). There was a reduction in the seed vigor (the most important germination parameter) by increasing the salinity level. The laser pre-treatment caused an increase of 39, 63, 46 and 100 percent in Afzal, Reihan, fajr 30 and Nosrat genotypes, respectively. The overall result showed a positive effect of the laser irradiation on the investigated traits.