مجله علوم و فنون هسته ای
سال سی و نهم شماره 3 (پیاپی 85، پاییز 1397)

Detection of low-energy anti-neutrino has certain applications in science and technology. Recently, the FLUKA collaboration, so-called the PEANUT model, has been developed which is capable of simulating all neutrino flavors from the threshold up to TeV. Here, the FLUKA code will be demonstrated as a neutrino event generator, upon emphasizing the interaction of low-energy electron anti-neutrino (i.e., those coming from nuclear reactors). The results which are reported in this paper show the applicability and capability of the code to be applied for such purposes. An important feature of the FLUKA code is its potential to track several types of particles (here most of them are considered as secondaries), and also the complicated geometries which imply that the present code is a powerful tool kit for neutrino engineering applications.

One of the factors that changes the UO2 fuel thermal conductivity is the generated porosity in the fuel due to increasing burnup. At high burnups, the structure known as rim region, is created. This is due to the Xe depletion process from the fuel matrix, porosity formation, and fuel grain recrystallization, which in turn change the fuel thermal conductivity. In this paper by the use of existing low temperature high burnup fission gaseous swelling model with the progressive recrystallization for UO2 fuel, the matrix swelling terms are calculated and the evolution of the total volume porosity up to burnup of 120 MWd/kgU is estimated. For the study the effect of porosity formation on the irradiated UO2 thermal conductivity, the HALDEN correlation of the thermal conductivity is selected. Then, a porosity correction factor is developed  based on an assumption that the fuel morphology is a three-phase type consisting of the pores, with no contribution to the matrix swelling and large pores due to intergranular bubbles with the contribution to matrix swelling dispersed in the fully dense material, composed of UO2 matrix and solid fission products. The predicted thermal conductivity, based on the present porosity correction factor, demonstrates an additional degradation of 25% due to porosity formation at the burnup levels around 120 MWd/kgU causing an increase in the fuel temperature.

In this paper, an analytical investigation has been presented on the excitation of nonlinear current densities and helicon waves resulting from the interaction of the electromagnetic pump waves in a semiconductor quantum plasma. For this parpose, a system of modified fluid equations has been used to find the nonlinear response of electrons in the semiconductor in the presence of an external magnetic field. It is shown that due to the interaction of two electromagnetic pump waves in the semiconductor medium, a pondermotive force at the beating frequency becomes finite and generates a helicon wave. Furthermore, the power carried by the excited helicon wave is calculated and evaluated relative to the typical parameters of a solid state plasma medium. The results indicate that the power of the excited wave gradually increases with the external magnetic field, as well as, the equilibrium density of the carriers, and decreases by the electron-phonon collision frequency.

A system dynamics model for simulating radionuclide generators inventory management decisions is presented in this research report. The radiopharmaceutical is generated gradually from another radioactive element, so called mother element in the radionuclide generators, and after each extraction of the produced radioactive material, so called elution, the radiopharmaceutical is produced in the proportion of the residue from the mother element. Based on the remained mother element, production time dependence,  mutual interaction of variables, nonlinear distribution function, and reproduction, lead to the incremental complexity of the mathematical model and cause the model making affair harder in common place operation research methods. In the proposed model appeared in this report, the above-mentioned factors are modeled and due to the nature of system dynamics models' development and the possibility of developing the boundary of the model, the feasibility of utilizing the model, as a basic one, in more complex modeling affairs is presented. The model behavior re-production tests and the system dynamics' extreme conditions, illustrate the validity of the proposed model. Ultimately, in this paper, several scenarios for the productivity raise are illustrated and twenty five percent improvement has been shown compared to the conventional models.

Performance of Three commercially available nanofilter membranes (PES-2 , NF-1 and NF-2) in terms of rejection, permeate flux, and membrane selectivity under a variety of operational conditions was evaluated for selective separation of uranium (VI) ions from iron (III). The membranes permeate fluxes were  decreased with an increase in the pH range of 3-6, while the rejection of ions was increased. Uranium rejection with these membranes was lower than iron rejection and the PES-2 and NF-1 membranes had the maximum membrane selectivity of iron over uranium at pH 4. The maximum membrane selectivity of NF-2, however, was 2.97 at pH 3. The PES-2 membrane had the maximum iron rejection of 72.25% at the pressure 10 bar. For NF-1 the rejection of iron and uranium was found to be relatively constant (about 97% and 84%, respectively) against increasing the pressure. As the pressure increased from 5 to 20 bar, iron rejection by NF-2 was remained constant (about 97%) but uranium rejection by this membrane was decreased from 84.06% to 70.46%. It was found that the effect of increasing the iron concentration from 0.12 to 1mM on the behavior of these membranes is  different. The maximum membrane selectivity of uranium over iron by the NF-1 and NF-2 membranes was 43.71 and 13.59, respectively, which showed that NF-1 has a very desirable performance. It seams that the relatively new process of nanofiltration has a good potential for selective separation of uranium from iron.

Extraction and transport of thorium (IV) from nitrate solutions was investigated using  polymer inclusion membrane (PIM), based on di(-2-ethylhexyl) phosphoric acid (D2EHPA) and poly(vinyl chloride) (PVC). This study investigates the influence of the main system parameters (i.e., pH of donor phase, type and concentration of acid  in acceptor  phases, percentage of D2EHPA in the membrane, initial Th(IV) concentration) on the extraction and transport process by means of  batch method. The transport factor of Th(IV) as high as 94.81% were recorded using a membrane composed of 45% D2EHPA, and 55% PVC (w/w) from a solution containing 112 mg L-1 Th(IV) in 0.0158 mol L-1 HNO3 (pH 1.8) into a solution containing 3 mol L-1 H2SO4.

 In this research, the layers of the sedimentary environment of the Pabdeh formation, which have different variation amounts of phosphate minerals (Apatite), were studied. The XRF and XRD analyses were performed for determination of the minerals and the radioactive elements, REEs and compounds for 54 selected samples (with high amounts of P2O5). According to the importance of the geochemical elements relations and their interpretation, the statistical analysis methods cluster analysisand principal component analysis, (PCA) were used. According to the results of the component correlation matrix, after rotation through the direct oblimin method, and normalizing with Kaiser method, the amounts of components and the ratio between them are well illustrated and the XRF results were divided into two principal components.

The studied area is located in the central Iran micro-continent, in the southern part of Lut block, 45 kilometers east of Bam Township. The main units of the area are mostly intercalation of pyroclastic rocks and lava layers in the age of Eocane, with the general trend of southwest- northeast and include high potassium calc- alkaline magma that their formation are related to the tectonic environments of magmatic arc and subduction zone. Argillic, silica, hematite, zeolite and chlorite alteration are observed in the area in relationship with uranium mineralization. The geochemical complexes related to uranium presence were identified in the study area. They are: complexes in relation with acidic and moderate rocks, including U-W-As-Mo-S-Cu-Ag, and complexes related to the basic igneous rocks, including U-Ni-V-Ag-Co-W-Mo-Cr-Cu-S. The main observed structures and textures in this area involve stock work, vein veinlet, corrosion, radial, release and peripheral membrane. The main mineralization in the area includes uranium secondary minerals contains Boltwoodite, Phosphuranylite and carnotite, manganese oxides, iron oxides and hydroxides, a few sulfide, zeolite mineral group and other minerals groups which mostly are formed under the influence of hydrothermal and late supergene processes. Based on a comparison pattern of mineralization in the area and its adjustment with the geological, alteration and geochemical conditions in uranium deposits, the most possible choice for mineralization type in the area has been introduced as volcanogenic uranium mineralization.

The stopping power, penetration and scattering of high energy electrons with different energy distribution functions into dense fuel and hot-spot (fuel core) have been considered for a fast-shock ignition scenario. The analytical calculations indicate that fast electrons with two-temperature energy distribution function penetrate more into the dense fuel, in comparison with the monoenergetic and exponential function, where it is consistent with the MCNPX simulation results. Furthermore, the scattering of energetic electron beams toward the outer surface of the fuel for five various fuel density and two fast ignitor wavelengths of 0.53 and 0.35 micron have been investigated. The results show that for the fuel mass smaller than  2 mg, the scattering of electrons reduce for the electrons with smaller energies and fast ignitor of smaller  wavelengths. Meanwhile, for the electrons with energy of the order ~3.5 MeV, two-temperature and monoenergetic energy distribution function deliver the highest and lowest energy to the main fuel and the central hot-spot, respectively.

One of the most important safety systems is spray system which is located in steel containment and has been designed to limit radioactive materials release, specially iodine, and to reduce the pressure and temperature in steel containment during events. The functions of mentioned system have been evaluated by the NPP designer by using probabilistic methods and the Risk Spectrum code. Some of the equipment, however, have not been simulated in the implemented modeling. In this article, by using the probabilistic analysis and the SAPHIRE code, the importance of the spray system’s elements in steel containment has been analyzed and the probability of system failures in various conditions has been calculated.