JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2013 | Volume:- | Issue:3 (65)|Papers Count:14

The response of an NE213 scintillator to Am-Be neutrons, in which the neutron and neutron-induced charged particles transports have been undertaken, has been simulated with the use of MCNPX’ PTRAC card whilst the scintillation light transport has been performed with Monte Carlo light transport code, PHOTRACK. The scintillation light output for different neutron-induced charged particles has been calculated using the validated light output curves. The experimental data on the response of the NE213 scintillator exposed to Am-Be source has been obtained with a neutron-gamma discrimination circuitry using zero-crossing method. The simulation data represent a good agreement with the corresponding experimental results.

The most considerable advantage of gel dosimeters is their unique ability to determine three dimensional dose distribution. Polymer gel dosimeters are, in fact, monomers distributed in a gelling matrix. Upon the irradiation, these monomers convert to polymers and as a result some of their detectable properties will be changed. One of them is the magnetic property which is detectable by the use of the MRI photography. In this research, the effect of magnetic field strength and echo numbers of a MRI system on the response of the MAGICA gel dosimeters was investigated. Consequently, after irradiation of the MAGICA polymer gel dosimeters, this dosimeter was imaged by 0.5T and 1.5T MRI systems with 8 and 32 echo, respectively. Sensitivity of the gels imaged by the 1.5T and 0.5T systems were 0.17±0.005 Gy/s and 0.16±0.005 Gy/s, respectively. The R2 values obtained from 0.5 T system were found to be higher compared with the 1.5T system in all the measured doses. Up to dose rate of 17.5Gy the resolution difference of the 1.5T and 0.5T imaged gels was ignorable and beyond this point this difference was increased notably. It can be concluded that when the absorbed dose is applied up to 17.5Gy the 0.5T MRI system is suitable but beyond this dose the 1.5T system is recommended.

The measurements of radon as a radioactive gas, when inhaled creates lung cancer risk in human, are of great importance for researchers. In this research, the response of a passive radon detector is determined based upon a new calibration method. The detector includes a chamber in which the radon gas can diffuse inside the cham ber and the alpha particles from the radon and/or its alpha emitter daughters are registered on the surface of a polycarbonate film at the bottom of the chamber. The new calibration method includes a traceable standard flow-through source of radon, connected to a designed calibration chamber with adjustable inner radon concentration. The uncertainty of the method is 5% with the confidence level of 95%. The sensitivity of the detection method is calculated to be 13.55 [tracks cm-2 (Bq lit-1 day)-1], and the results of an international intercomparison show that the differences between the measured values by the system are less than 5% in comparison with those of the reference values in three radon levels; that is, low, medium, and high concentrations.

Octadecyl silica cartridge modified with Cyanex302 was used for the separation and preconcentration of thorium (IV) and uranium (VI) from aqueous solutions. The influences of analytical parameters including pH, and the amount of Cyanex302 were investigated on the adsorption of analyte ions. The maximal capacity of the cartridges modified by 30mg of Cyanex302 was found to be 20 mg/L of uranium and thorium.

Our aim in this work was to develop a reliable technique to accurately determine the amount of Yttrium-90 in Strontium-90 used for therapy. Yttrium-90 which can be used for clinical purposes should be in a very high radionuclide purity, therefore a suitable quality control method must be applied. Also, Yttrium-90 has a short half-life, so speed is very important for determination of its purity. For this purpose, a simple paper chromatographic method was designed and used in the present study. In this method two extractants HDEHP and Cyanex272 were utilized and the ability of hydrochloric and nitric acid for separation of Yttrium-90 from Strontium-90 was evaluated. The results showed that large differences between Rf values of Yttrium-90 and Strontium-90 radionuclides were explored by using HDEHP as an extractant and mobile phase containing 0.9% saline and 0.1M nitric acid. Under these conditions, the radiochemical control of Yttrium-90 could be achieved.

Fukushima Dai-ichi nuclear power plant accident in Japan seriously questioned the worldwide presumed trust about the safety of existing nuclear power plants. Neither the advanced facilities nor the existing emergency response preparedness could hamper the rapid expansion of the accident, resulting in the world's most severe nuclear crisis after the Chernobyl accident. This paper presents a chronologic study of the accident and the responses to it in order to recognize the main phases of the crisis management in Fukushima. The study reveals that out of the total five recognized phases, the three first ones have mainly gone through by inevitable reactions, situation assessments, and data gathering for a comprehensive response planning. Investigating the influence of each phase on expansion of the accident is indeed of vital importance for effective planning for responding to similar accidents. Deficiency of preventive measures leading to the occurrence of the accident and incompetence of the Japanese nuclear safety infrastructure in hindering the rapid expansion of the crisis, are also discussed. Following a root cause analysis, the paper concludes with proposals for preventing similar accidents and shortening the duration of the first phases of the aftermaths.

U-Tube Steam Generator (UTSG) is a crucial component in nuclear power plant with the pressurized-water reactor. Ineffective control of the Steam Generator (SG) water level in the secondary circuit of a nuclear power plant can lead to frequent reactor shutdowns or damage the turbine blades. The difficulties in designing an effective level controller for UTSG arise mainly from the following two factors: first, high nonlinearity and second, non-minimum phase characteristics due to the so-called “swell and shrink” effect. Therefore, designing a suitable controller is a necessary step to enhance the nuclear power plant availability factor. The purpose of this paper is to design, analyze and evaluate a water level controller for U-tube steam generators using dynamic sliding mode control based on a nonlinear model of them. The above mentioned method is easy to implement in practical applications. Moreover, the dynamic sliding mode control exhibits the desired dynamic properties during the entire output-tracking process, independent of disturbances and uncertainties. To validate the designed controller, a steam generator simulator is used with simulation of occurance of an accident in a real nuclear power plant. The simulation results show the performance, robustness, and stability of the proposed controller.

Thermal processing affects functional compounds of foodstuffs significantly. In the present research, the effect of gamma ray on the pomegranate juices of Malase Momtaze Saveh and Alak Saveh cvs was studied on some physicochemical properties, functional compounds, antioxidant activity and color of pomegranate juices. There was no significant difference in terms of pH, total titratable acidity and soluble solids content (oBrix) by 0-3 kGy gamma irradiation doses. Irradiation had no significant effect on the reduction of phenolic content of the samples. The total anthocyanin content of pomegranate juices significantly reduced after irradiation. The degradation percentage of the total anthocyanin content of juices obtained from Malase Momtaze Saveh and Alak Saveh arils was 34 and 29%, while these values was about 32 and 30% for juices from the whole pomegranate, respectively. By increasing the irradiation dose, the antioxidant activities of the samples in comparison to control had a decreasing trend, albeit insignificantly. In comparison with the control samples, the treated juices showed significant changes in hunterlab parameters. The L* values of irradiated samples significantly increased, while a* and b* values significantly decreased. Overall, the minimal destructive effects of gamma irradiation on functional compounds and physicochemical characteristics of pomegranate juice can be achievable at low-dose irradiation.

Core radionuclide inventories calculations were performed for Tehran Research Reactor (TRR) using computer code ORIGEN 2.1. At first a comparison was made between the present calculations and the existing results for the source terms of the equilibrium core that had already been presented in the Safety Analysis Report (SAR), which showed a good agreement. Then, the core radionuclide inventories calculations were carried out for a recent TRR core configuration. The resulting source terms may be used for the evaluation of radiological consequences of the corresponding accidental release of the radio nuclides from the TRR.

A set of Nuclear Reactor model V-446 applied in design AES-91/99 is regarded as an optimized project of reactor VVER-1000 on the basis of reactor model V-320. Improving the neutron- physics characteristics of the active core along with the reconstruction of reactor basic sections made the implementation of uranium- gadolinium fuel possible. Furthermore, by taking into consideration the negative coefficients of thermal reactivity for fuel pellet, reactor power and coolant liquid, as well as by designing the supplementary control line special for beyond-design accidents and also by carrying out hydraulic tests in the system of preventing an increase in the pressure of the primary circuit and also by ensuring the concept ˝Jeakage before breakage˝ with the help of the new control systems and special trouble-shooting of primary circuit equipment, valves and lines, we have opened up a new vista which will increase the safety coefficient of new generation contrary to the old models of VVER-1000.

A radially-oriented hydride (RH) has been known to deteriorate the final properties of fuel claddings. One of the most effective factors on formation of these hydrides is cold working process. In this work, we were concerned with two different rolling processes to find their effects on mechanical and corrosion properties, as well as, on the hydride orientation of the final tubes. The first process used was our conventional method with six different rolling passes and the other was just involved with four passes. All the microscopic, hydride orientation, mechanical and corrosion behaviors of two samples were examined. The experimental practices showed better results of newly designed cold working process in comparison with our conventional method.

2D and 3D numerical models of a steam generator for VVER-1000 type nuclear reactors used in the nuclear industry is presented. For the calculation Euler-Euler approach is applied for modeling the boiling heat transfer, boiling and recondensation. In the 3D model, the secondary side of the steam generator is simulated by the porosity model presented earlier by Stosic and Stevanovic. In the Porosity model, the tubes of the primary circuit are not described in detail, but they are modeled as sources of enthalpy and pressure loss. The physical models were implemented by user-defined programs in ANSYS-CFX12.1 computational fluid dynamics software. The results of the 3D thermal-hydraulic modeling of the steam generator in the Russian type VVER-1000 NPP for the full load operating condition are presented. The results clearly illustrate a void fraction distribution. Moreover, the role of submerged perforated sheet is investigated. The results are compared with a published paper in 1999 by Stevanovic. There is a good agreement between the introduced calculation. In addition, in the 2D model, the superficial velocity of water vapor is calculated as well.