JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2007 | Volume:- | Issue:1 (39)|Papers Count:9

In this paper, time dependent neutron transport in fissionable media is simulated by Monte Carlo method, and the neutronic parameters are estimated. In this article, the effective multiplication factor, neutron lifetime, and flux distribution in steady state condition are calculated. The comparison of the results obtained by this method, with those of the experimental measurements and the other calculations has shown that they are in very good agreement.

Storage of high-level waste and spent fuels from nuclear reactors is a main concern in the field of nuclear engineering. Generally, deep geological repository is suggested for this purpose. Heat transfer by high-level waste and spent fuels and their impacts on environment in a deep geological repository is an important subject for study. In this paper a three dimentional model for heat transfer in canisters and a deep tunnel was developed. FLUENT 6.0 with K-e turbulence model was used to simulate the turbulent flow with and without radiation. The influence of parameters such as heat flux, air velocity, and depth of tunnel and the ground and canisters surface temperature were studied for two cases of forced and natural convection. For the air velocity of 0.6 m/s with 67 canisters in the tunnel and 360k W/m2 the initial heat flux for each canister, it is shown that the surface temperature reaches its allowed maximum limit of 93°C for concrete.

Radioactive protection is one of the most important subjects in nuclear power plants safety. Analysis of BNPP spent fuel pool shielding, as a main source of energetic g-rays was the main goal of this project. Firstly, we simulated the reactor core using WIMSD-4 neutronic code and the amount of fission product in the fuel assembly (FA) was calculated during the reactor operation. Then, by obtaining the results from the previous calculation and by using MCNP4C nuclear code, the intensity of g-rays was obtained in layers of spent fuel pool shields. The results have shown that no significant g-rays passed through these shields. Finally, an accident and resulting exposure dose above the pool was analyzed.

In this paper, it was attempted to study the temperature dependence responses of some high dose dosimetry systems that are commonly used in Radiation Application Research School, located in the province of Yazd, during the irradiation. In fact, the correction of the read out response of the dosimeters to that of the real absorbed dose values is very important, especially if one needs to measure the precise dose values in medical devices and in foodstuff materials. This is because of the fact that the uncertainty in the measurements is proportional to the sensitivity of the dosimeters, and so. it can lead to irrecoverable results in the irradiated products. Thus, in this work we tried to investigate the temperature effects on the dosimeter response and obtain its variation as a function of temperature. The correction coefficient for each of the dosimeters has also been defined.

Ga-68 is a radioisotope material with a half life of 68 min. As it has a specific decay mode, it is a positron emitter and hence, is popularly .used in nuclear medicine. The only way to obtain these nuclides is to produce the mother nuclease which is Germanium-68. There are many nuclear reactions from which the Ge-68 is obtained, however, the best reaction is 69Ga (p,2n) 68Ge. The cross section of this nuclear reaction was calculated with the ALICE-91 Code and the result was compared with the practical work made by other researchers, and it was acceptable. Having the cross sections in mind, the best proton energy was calculated to be between 20-25 MeV. Further research showed that Ga2O3 is the best type of target material. Therefore, it was necessary to design and make a suitable target holder for these kinds of compositions, which for the first time in Iran was demonstrated in the Atomic Energy Organization of Iran (AEOI). The thickness of the target, bearing in mind the rate of energy loss inside the target material, was calculated with the SRIM Code and the Ga2O3 tablets were made with FT-IR facilities at the Nuclear Research Center for Agriculture and Medicine (NRCAM). They were, then bombarded with 22.5 MeV proton energy and the beam currents of 2 and 10 mA. Two weeks after the bombardment the radio chemical separation of Ge-68 was accompolised with concentrated acid RN03 and by applying heat. Then, the acid solution was evaporated till dried, after that, an EDTA solution (0.005 M, pH=11) was added to recover the Ge-68. By passing the EDTA solution with the rate of 0.5 ml/min through the Al203 column, the Ge-68 radioisotope was observed. Then, about 50 ml of EDTA (0.005 M, pH=11) was passed through the loaded column, where almost all the natural Gallium impurities were removed. The prepared generators were milked many times with EDTA solution (0.005 M, pH=8) and the leakage of Ge-68 nuclease and natural Gallium were determined. The average of the mother nuclides (Ge-68) was about 0.03% and the natural Gallium was 0.7 mgl-1, which is compatible with the reports of other researchers.

The mechanism of action and metabolism of clozapine which is considered as a complicated drug used in psychopharmacology, is not completely understood. The effects of this compound in human body are related to some interactions of this compound with serotonin and dopamine neurotransmitter receptors. To further elucidate the mechanism of action and to support the ongoing drug metabolism studies, [14C] clozapine with a suitable radiochemical purity was synthesized in the Nuclear Science Research School of the AEOI. In this report, the radiochemical and chemical purity of [14C] clozapine were determined by the liquid scintillation and the reversed phase-HPLC, respectively. Separation of [14C] clozapine and its synthesized interface products were carried out using a C8 optimal column and a UV detector at 254 nm. The mobile phase consisted of acetonitril- buffered aqueous solution of sodium phosphate with a flow rate of 1ml/min. The detection limit and the analytical precision of RP-HPLC method were 0.1ng and 1-3.4%, respectively. The chemical purity of the synthesized clozapine was >99%. For determination of the activity and the radiochemical purity, a liquid scintillation spectrometer was used and the counting was made by direct addition of samples to ACS (Amersham) solution. The specific activity of the synthesized clozapine was 10mCi/mg and the radiochemical purity higher than 99% was obtained.

Uranium (VI) forms a complex with citric acid. This complex can be used for a highly sensitive determination of uranium by adsorptive cathodic stripping voltametry using a hanging mercury drop electrode as working electrode. Influences of effective parameters such as pH, concentration of ligand, accumulation potential and accumulation time on the sensivity were studied. The Detection limit obtained under the optimal experimental condition is 1.9x10-9 M after 150s of the accumulation time. The peak current is proportional to the concentration of U (VI) in the range 1.9x10-9 to 4x10-7M.

The present work focused on the catalytic destruction of Dowex cation exchange resin with hydrogen peroxide in the presence of Fe (II) ion catalyst. A 0.005 mol/lit of Fe (II) concentration with the continuous mixing rate of 500 sec-1 was used for catalytic decomposition of 2 grams of dried resin (80oC, 8 hr) with the efficiency of destruction or decomposition of 90 and 97 percent (carbon reducing percent), where it was needed to use 30 and 45 ml of hydrogen peroxide of 30%, respectively. This amount of resin can be decomposed to soluble polystyrene sulfunate just with 10 ml of hydrogen peroxide of 30% and with 20 ml of hydrogen peroxide we can reach %80 efficiency. Also, it was found that the intermittent addition of hydrogen peroxide is showing a good effect, and by changing the Ph between 2 and 4 no significant effect on the reaction efficiency was found. The optimum conditions based on this study are as follows: 0.5 ml/min hydrogen peroxide, 95 to 100oC, 3.5 pH and 0.005 mol/L of Fe (II) concentration with continuous mixing rate of 500 sec-1.