مجله علوم و فنون هسته ای
سال سی و هشتم شماره 3 (پیاپی 81، پاییز 1396)

Safety and related categories are of importance in all fields of nuclear industry, especially as regards the nuclear reactors. One of the most important safety aspects in the nuclear reactors is the shutdown system, each reactor requiring at least one. One of capabilities that can improve the safety of a nuclear reactor is adding another shutdown system to it. For making any change as design and locating second shutdown system in the reactor, attention to special characteristics of any reactor and design basis criteria such as redundancy, diversity, separation, single failure criteria and fail-safe mode is necessary. A second shutdown system based on the injection of neutron absorber is designed with considering its standards and requirements for Tehran Research Reactor. The proposed design has a high reliability that fulfils the most important design requirement, which is having enough negative reactivity, has the ability to maintain the reactor in subcritical state in a determined period of time with the necessary safety margin and for needed time duration. Calculations and simulations have been done using MCNPX code. This design has some negative effects on different core characteristics, albeit minimized by the designed structure optimization.

Spallation process is the most important neutron generation method in industry, medicine, etc. This process in the subcritical reactor core is also another technique. In this research, we study the neutronic behavior of the spallation targets consisting of U-238 and Th-232 materials, by MCNPX code. The parameters under study comprise the spallation neutron yield, deposition energy, target geometry; angular spectrum of the neutron output, gas rate and residual mass spectrum. The results show that geometry has the greatest impact on the neutron output spectrum, but not on the residual mass spectrum. Numbers of neutrons per energy unit are stable at higher energies of 1 GeV, then the changes in neutron generation rate are reduced. Furthermore, hydrogen which is the principal factor in swelling of spallation target, consists of about %88 of gas production.  

In this paper, the optical density distribution function obtained from the radiographic films at the voltages of 80-150 kV was investigated. Steel plates of 30×30 mm2 with thicknesses of 2 and 8 mm were irradiated according to the European standards with different currents at various times. The information of the radiographic films was converted into 8-bit numeric data by using a laser scanner with a resolution of 3200 dpi. The histograms obtained from these scans were compared with all applicable probability functions. Due to the large number of the employed probability functions, their compatibility was first assessed on the best and simplest histogram. Afterwards, the selected functions were used for the remaining films. In this way, the best probability distribution function was determined. The same steps were taken for radiographic defects. Furthermore, the degree of adaptation of the probability distribution functions applied to the base metal and the defects regions was also evaluated.  

Since the local quench which induces electro-thermal instability if a local energy input exceeds a certain threshold called minimum quench energy (MQE), the normal zone propagates along the superconductor. Therefore, the rate of the normal zone spreading as a quench propagation velocity (νq) is an important factor in the quench detection and protection. This paper focuses on the measurement of νq as a self-protection parameter in a short sample of a high temperature superconducting Bi-2223/AgMg tape by applying the localized heat pulses, and MQE as a superconducting stability criterion. In addition, the current dependences of MQE and νq were verified in which by increasing the transport current, the rate of decreasing of MQE and the rate of increasing of νq were measured. These experiments have been done in nitrogen vapor without applying any magnetic field.

In this paper, BSCCO bismuth-based superconductor material is prepared by the electrodeposition method. The electrolyte compositions are based on bismuth nitrate [Bi(NO3)3] copper nitrate [Cu (NO3)2], calcium nitrate [Ca(NO3)2], strontium nitrate [Sr(NO3)2] and DMSO [(CH3)2SO] as the solvents. The properties of BSCCO are studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). In the electrodeposition method, copper (Cu) and silver (Ag) are used as the anode and cathode, respectively. The optimal efficiency for electrodeposition of a superconductor material is observed at voltage: 5V and temperature: 55˚C. BSCCO-2212 phase in the electrodeposited sample is confirmed by XRD. The sample shows nano-leaf morphology, with a transition temperature (Tc) is 85 K.

In the present research work, high concentration amounts of fluoride ions in nuclear waste produced during uranium recovery from the three groups of uranium conversion factory scraps (C36, C37, 56P) were removed by the chemical precipitation method. In this method, calcium chloride due to its high solubility in water and lower sludge production in comparison with other compounds of calcium was used as a precipitant agent. The effects of different parameters such as: the type and concentration of coagulant, pH, the concentration ratio of calcium to fluoride, time and rate of stirrer, aging time and the temperature of precipitation on the removal of fluoride were optimized. The results show that the yield of fluoride removal in these samples relates to all of these parameters with the exception of temperature. In spite of the theoretical calculations, the amount of fluoride in final wastewater for C36, C37, 56P decreases to 3.6, 5.8 and 4.6 ppm, respectively, which can be released to the environment directly at a slight dilution. The results show that calcium chloride in the optimized conditions, is a suitable precipitant agent for the effective decrease of high concentration of fluoride in the real sample. Also, the performed experiment, by using the industrial grade calcium chloride product, shows the similar result which confirms the possibility of this method being used in industry.  

According to the IAEA and USNRC (United State Nuclear Regulatory Commision) regulations, calculating a strong ground motion during an earthquake is of great importance for the design of nuclear facilities, especially nuclear power plants. In the absence of precise seismic studies and in case of severe earthquakes, many radioactive contaminants are released into the environment, with irreparable physical and financial losses, hazarding the nuclear facilities, people and the environment. In this research, in order to develop the earthquake attenuation relationships for Boushehr, an important region, simulation of the ground motion was used along with the stochastic finite fault method. The results obtained from the simulation have been compared with the results obtained from the valid world relations for the Zagros region. Evidently, they show good consistency. The proposed model is a theory-empirical relationship of the Bushehr susceptible region, which can be used to assess the safety of the existing nuclear power plant in Boushehr and to design new nuclear power plants in the future.

Gamma irradiation has shown to greatly reduce potential microbiological risk of fresh fruits, resulting in improved microbial safety as well as extending their shelf life. The effects of 0.5-2 kGy gamma doses on some physicochemical, microbial and sensory properties of fresh barberry fruits (Berberis vulgaris) during the refrigerated storage for 40 days were evaluated. The decrease trend of titratable acidity and an increase trend of pH and total soluble solid were reduced by gamma radiation during storage. The weight loss of the packed barberry was not significant between control and treated samples. The total anthocyanin and total phenolic contents of barberry fruits decreased in a dose-dependent manner immediately after irradiation and after subsequent storage. Gamma irradiation did not affect color indices of the fresh berberis fruits, but a significant decrease in color indices were observed during the storage time. The microbial growth was significantly inhibited, especially at doses higher than 1.5 kGy during the storage. Based on the panelist suggestion, the samples irradiated at >1.25 kGy were still between the acceptance limit at the end of the storage period. In general, it is recommended that according to the effect of gamma radition on physicochemical, microbial and sensorial characteristics, doses of 1.25-2 kGy could be used.

Proton acceleration process by the generated sheath in the rear-side of an Al target in the interaction of P polarized laser with the pulses duration of  ≥40 fs and intensity of 3.6×1019 W cm-2 has been experimentally and  numerically studied. The results show that by employing the positively chirped pulse, the proton cut off energy and the number of the accelerated protons are increaesd in comparison with an unchirped and negatively chirped pulse interactions. After that, the electron heating process in interaction of positivly and negativly chirped  pulse is investigated and correlation between the chirped parameter and produced electrostatic field in the backside of the target is studied. Particle- in-cell simulation results show that the electron heating process and consequently the electrostatic field for proton acceleration goal are significantly increased by employing the positively chirped pulse campared to negativly unchirped conditions.

Ammonium uranyl carbonate (AUC), an intermediate material in the process of conversion of yellowcake to uranium hexafluoride, was produced by injection of an aqueous solution of ammonium carbonate (AC) into uranyl nitrate solution. The target parameter in optimization of this process was the yield of the precipitation, as morphology and size distribution of AUC play no role in its post processing to UF6. The aim of the current study was the experimental investigation of the effects of the process variables on the yield of AUC precipitation. The results showed that the flow rate and flow pattern of the injection of the AC solution, aging time, impeller speed, and temperature had little effects on the yield of AUC precipitation. On the other hand, the yield was increased by increasing the ammonium carbonate to uranyl nitrate molar ratio, ammonium carbonate concentration, and uranyl nitrate concentration. However, it decreased by increasing the molar ratio of CO32- to NH4+ ions in the ammonium carbonate solution.