JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2011 | Volume:- | Issue:4 (54)|Papers Count:8

Tehran Research Reactor (T.R.R.) is a pool-type, 5 MW thermal research reactor. One probable event is that if some external objects or debris fall down into the reactor core and cause obstruction of the coolant flow through one of the fuel assemblies, decreasing the surface flow area, ceases the coolant flow, and also raises the fuel and sheaths temperature. Thermal hydraulic analysis of this event has been studied using RELAP5 system code. This report is related to the partial and total obstruction of a single Fuel Element (F.E.) and cooling channel of 27 F.E. equilibrium core of the T.R.R. Such event may lead to severe accident for such type of research reactors, since it may cause a local dry out and eventually loss of the F.E. integrity. Two scenarios are analysed in order to emphasize the severity of the mentioned accident. The first is a partial blockage of hot F.E. which is considered for four different obstruction levels of the nominal flow area: 25%, 50%, 75% and 93%. The second is related to an extreme case which consists of the total blockage of the same F.E. The reactor power is derived through the kinetic point calculation in the RELAP5 code. The point kinetic feedbacks including the fuel temperature (Doppler coefficient) and the coolant density coefficient have been considered through the applied model. The main results obtained from the RELAP5 calculations are as follows: 1. In case when the flow blockage is under 93% of the nominal flow area of an average F.E., only the increase of the coolant and clad temperatures are observed with no integrity of the F.E. consequences. The mass flow rate remains sufficient enough and cools the clad safely 2. In the case of a total obstruction in the nominal flow area, it is seen that the severe accident is due to dryout conditions and reaches promptly, while melting of the cladding occurs.

The project of design and construction of linear electron accelerator is being performed by the Ministry of Science, Research and Technology and Institute for Research in Fundamental Sciences (IPM). The aim of the current research is to achieve the knowledge and the technology of manufacturing the components of linear accelerator, one of these components is buncher. In this paper, two types of bunchers are introduced, while the disk-loaded type has been selected to be fabricated. Studying the electrons motion in the field through the aperture of the disks and using the equations of disk-loaded waveguide theory, the dimensions of the desired buncher for this project were obtained. MATLAB software and SUPERFISH code were used in calculations and simulations. The design led to the initial and final phase ranges of 348 degrees and 50 degrees, respectively. The mentioned values for the initial and final phase ranges resulted in a bunching factor of about 7 that is appropriate for this type of the bunchers.

The goal of this article is calculation of the electric field at the end of loaded path in solid-state track detectors. For the calculation Laplace-Equation has been solved numerically. By solving the equation, upon considering a specific potential at the boundary of the region, in addition to calculating the electric field at the end of path, the parameters which are affecting the electric field have also been investigated.

The 153Sm production by neutron bombardment of a natural samarium target produces 154,155,156Eu impurities. Therefore, it is important to investigate amount of impurities and their separation methods. In this study, 153Sm was separated from Eu radioisotopes by ion exchange chromatography. Natural Sm2O3 powder was dissolved in HNO3 and encapsulated in aluminum foils. The target was irradiated by the Tehran 5MW Research Reactor with the neutron flux of 5×1013 n cm-2 s-1. The irradiated target was dissolved in HCl and was injected into a chromatography column that was packed with Dowex-50Wx8, 200-400 mesh resin. As a result, 153Sm was separated with the recovery yield of more than 65% with a purity better than 99.8% from Eu impurities.

In this research, separation of fluoride and uranyl ions from high content nitrate and fluoride solution, by g-Alumina in moving and fixed bed methods, has been studied. In this investigation, the effect of some principal parameters such as, alumina weight, its particle size, and pH on the efficiency of separation of these ions from uranium solution, has been optimized. In the moving bed process, in fact, for decreasing pH, the best and economical condition for uranium extraction by solvent extraction process with TBP has been made available, and therefore it leads to save 800m3 HNO3 as a good advantage. In addition, in the fixed bed process, at an optimum pH, the concentration of uranyl and fluoride ions in the final raffinate decreased for uranium in a range of 50 ppb to 1.3 mg/L, and 170 ppb for fluoride. The effect of adsorption parameters on desorption of these ions was investigated and optimized by sodium carbonate solution. Uranium desorption from the column by sulfuric and nitric acid and sodium carbonate solution was carried out easily, and by sulfuric and sodium carbonate solution 99% recovery was obtained.

Because of low grade of thorium and uranium in the Zarigan mineral deposit, the pre-concentration operation prior to leaching is necessary. From X-ray diffraction analysis results, it was clear that this ore has large amount of other minerals such as Feldespat, Quartz, Hematite, Titanomagnetite, and rare earths. In this paper the thorium enhancement grade in Zarigan deposit by using gravity, magnetic and electrical separations methods is reported. The output of a Jaw crusher was ground to 85 micron by using ball mill. Then about 95% of SiO2 was separated by using shaking table separation. The heavy concentrate of shaking table was processed by a high intensity magnetic separator and then the magnetic concentrate separated by a low intensity magnetic separator. Finally, the non magnetic concentrate of low magnetic separator was processed with the electrical separation. The grades of thorium and uranium in the non magnetic concentrate of low magnetic separator were increased to 4000 and 5000 ppm, respectively where only 15% of the initial feed (ore) was transferred to this concentrate. Therefore, this resulted in a decrease of acid consumption in the leaching processes and the efficiency enhancement of the process. The pre-treatment circuit of this ore was designed as Jaw crusher/ball mill/shaking table/high-magnetic separator/low-magnetic separator/electrical separator, respectively.

In this investigation, the standard type tests performed on the LiF: Mg, Ti chip samples which have been produced in Iran. The dosimetry tests are consisting of sensitivity, homogeneity, linearity, reproducibility, minimum measurable dose (MMD), self and residual doses. The obtained results show that some of the tests such as sensitivity, minimum measureable dose, self and residual doses fulfill the criteria given by IEC 61066 and ASTM E668 standards, however, the remaining tests show some discrepancies in comparison with the standards. Also the sensitivity was measured to be 0.92 of that of commercially available TLD-100 (Harshaw) sample. So, the produced LiF: Mg, Ti dosimeter can be used in a routine personal/environmental and medical dosimetry with considering its precision.

Accurate modeling of omni-directional assay variograms for a deposit, plays a very significant role in the results of 3-D assay estimation and therefore its distribution within the estimation blocks. The high grade variations in uranium deposits render the significance of accurate variogram modeling. By this research, some models have been fitted to the experimental variograms with 0.5 meter composited uranium assay data, resulted from chemical analysis of drill core samples, from a uranium deposit. Reciprocal validation test has been applied for selection and evaluating the effect of suitable results, from multi-structural models in compare with other proper types of models. Validity study of the models is conducted through the reciprocal validation test, based on a series of criteria such as the average of differences and the difference of estimated values and raw data, in order to determine the validity accuracy of the fitted model. It is concluded that the dual-structure spherical model has a higher validity and furthermore reveals the significance of minor structures in variogram modeling, specifically for uranium deposits.