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Öğe Burnup extension of the Fixed Bed Nuclear Reactor using alternative fuels(PERGAMON-ELSEVIER SCIENCE LTD, 2013) Alkan, MahmutTime evolution of criticality and burn up grades of the Fixed Bed Nuclear Reactor (FBNR) are investigated using alternative fuels. Neutron transport calculations are performed by using XSDRNPM/SCALE 5 codes. Firstly, the calculations were performed to search the optimum compositions of UO2/Reactor grade-PuO2; UO2/weapon grade-PuO2 and of UO2/MAO(2) that would result in the similar initial value of keff as that of UO2, the original fuel of FBNR. Fuel component has been varied from 1% to 100%. The fuel compositions have been obtained with UO2: (1) 35% RG-Pu (2); 19% WG-Pu O-2; (3) 50% MAO(2). After that, ken burnup and operation time values of the fuels were compared. The temporal variation of the criticality keff and the burn-up values of the reactor have been calculated by full power operation for a period of 18 years. The criticality in compositions of Reactor grade-PuO2/UO2; weapon grade-PuO2/UO2 and MAO(2)/UO2 starts by k(eff) = 1.2742, 1.2726 and 1.2783 for the fuels compositions, respectively. These mixed fuels would allow full power reactor operation for >= 14 years and burn up grade can reach 104,646, 101,990 and 80,798 MW D/T, respectively. On that way, the hazardous nuclear waste product can be transmuted as well as utilized as fuel. (C) 2013 Elsevier Ltd. All rights reserved.Öğe EFFECT OF PRE-STRAINING ON THE SPRINGBACK BEHAVIOR OF THE AA5754-0 ALLOY(INST ZA KOVINSKE MATERIALE I IN TEHNOLOGIE, 2011) Toros, Serkan; Alkan, Mahmut; Ece, Remzi Ecmel; Ozturk, FahrettinThis study presents the effect of pre-straining on the springback behavior of the AA5754-0 aluminum-magnesium (Al-Mg) alloy sheet under V bending by an experimental and finite-element simulation studies. Pre-straining ranges from 0 To to 11 % were applied to the samples, which were bent on a 60 degrees V-shaped die for the springback evaluation. Commercially available finite-element software, ETA/Dynaform, was used to simulate the 60 degrees V-die bending process. The dynamic explicit finite-element method for pressing and the static implicit finite-element method for the unloading phase were used for the simulations. The results from both the experiment and the simulation indicate that the pre-straining has no positive effect on the springback compensation.Öğe Effect of pre-straining on the springback behavior of the AA5754-0 alloy(2011) Toros, Serkan; Alkan, Mahmut; Ece, Remzi Ecmel; Ozturk, FahrettinThis study presents the effect of pre-straining on the springback behavior of the AA5754-0 aluminum-magnesium (Al-Mg) alloy sheet under V bending by an experimental and finite-element simulation studies. Pre-straining ranges from 0 % to 11 % were applied to the samples, which were bent on a 60°V-shaped die for the springback evaluation. Commercially available finite-element software, ETA/Dynaform, was used to simulate the 60°V-die bending process. The dynamic explicit finite-element method for pressing and the static implicit finite-element method for the unloading phase were used for the simulations. The results from both the experiment and the simulation indicate that the pre-straining has no positive effect on the springback compensation.Öğe Investigation of formability of metallic bipolar plates via stamping for light-weight PEM fuel cells(Pergamon-Elsevier Science Ltd, 2020) Karacan, Kivanc; Celik, Selahattin; Toros, Serkan; Alkan, Mahmut; Aydin, UgurBipolar plates (BPs) are one of the main members which constitute a significant percentage of a fuel cell system in terms of cost, weight and structural strength. Although frequently used graphite BPs have low density, high conductivity and corrosion resistance, machining the desired flow channels on the graphite plates is an important issue. On the other hand, metallic BPs can be considered a reasonable alternative material to graphite in the view of the material cost, fabrication of flow channels and some post-processes in which the largescale manufacturing of graphite BPs is more complex compared to cutting and stamping processes for metal ones. This study offers a comparison of the formability of four different metals with four flow channel depths as bipolar plates formed by stamping. 304 Stainless Steel (SS 304), pure Titanium Grade2 (CP-Ti) and Aliminium (Al 6016 and Al 3104) are chosen as the BP materials. A serpentine type flow channel with two different channel widths are formed on to 0.1 mm thick sheets. The channel width is chosen as 1.2 mm and 1.8 mm for the channel depths of 0.36 mm-0.55 mm, and 0.54 mm-0.82 mm, respectively. The stamping processes of the BPs materials are simulated via commercially available eta/ Dynaform v5.9.4. software and formability characteristics are obtained for sixteen various cases. As a result, it is determined that SS 304 is the more appropriate material in the view of the formability for such a complex form. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Investigation of Neutronic Performance in Fixed Bed Nuclear Reactor (FBNR) With Fuelled (239Pu/Th)O2(Gazi Univ, 2013) Alkan, Mahmut; Acir, AdemIn this study, the neutronic performance analysis in a fixed bed modular nuclear reactor (FBNR) was performed. The effect of the (Pu-239/Th)O-2 mixture fuel of neutronic performance were investigated. Neutronic calculations were conducted by using SCALES code. Firstly, criticality (k(eff)) value compared 9 % enrichment UO2 was computed. The mixture fuel ratio was obtained as % 6 (PuO2)-Pu-239 + % 94. As a result, the operation times passed until the k(eff) value reached a level of 1.06 was computed as similar to 5 year whereas, the corresponding burnup value wase obtained as similar to 33 000 MWD/T.Öğe Investigation of the Performance of CANDU Reactor Using Different Uranium (Uo2, Uc, U3si2) Fuels(Gazi Univ, 2005) Acir, Adem; Alkan, Mahmut; Baysal, EsrefCanadian Deuterium-Uranium Reactor (CANDU) and Light Water Reactor (LWR) have significant share on supplying world energy. LWRs use low enriched uranium fuel with similar to 3.5 U-235 whereas CANDU utilizes natural uranium fuel with similar to 0.71 % U-235. In this work, neutronic performance of CANDU reactor, temporal change of fissile fuel breeding and fission power production were investigated in the CANDU reactors with different uranium (UO2, UC, U3Si2) fuels. Calculations were done with the aid of one dimensional computer code of SCALE 4.4a. According to calculational results, by taking k(infinity) = 1.06 as reference limit, burnup grades were found as 7700, 8900 and 7400 MW. D/MT and operation periods were obtained as 170, 260, 190 days for these fuels, respectively. According to these results, UC fuel showed better nuclear performance than natural UO2 and U3Si2 fuel with respect to criticality and burn up grade.Öğe KATI OKSİT YAKIT PİLİNDE YAKIT KULLANIM VERİMİNİN DENEYSEL OLARAK İNCELENMESİ(2018) Çelik, Selahattin; Alkan, MahmutKatı oksit yakıt pilleri (KOYP) yüksek enerji dönüşüm verimlerine sahip enerji üreteçleridir. Yakıt pillerinegönderilen hidrojen ve hava miktarının arttırılması performansı iyileştirmektedir. Bununla birlikte,kullanılmayan yakıt miktarı da arttığından yakıt kullanım verimliliği düşmektedir. Bu çalışmada farklı debideğerlerinde bir katı oksit yakıt pilinin yakıt kullanım verimi araştırılmıştır. Debi değişimi yakıt kullanımverimini önemli derecede etkilediği gibi sabit debilerde çalışma potansiyelinin de yakıt kullanım veriminietkilediği görülmüştür. Literatürde geliştirilen KOYP pillere ait yakıt kullanım verimi değerlerinin, geneldehangi voltaj ve debide elde edildiği yazmamaktadır. Bu durum güce endeksli olmayıp sonuçların yanıltıcıolmasına neden olabilmektedir. Bu çalışmada güce endeksli yakıt pili verimleri karşılaştırmalı olarakgösterilmiştir. Yüksek voltaj aralığında yakıt kullanım veriminin %85’lere kadar çıktığı gözlemlenmiş olup buverimlilikte 90 mW.cm-2 güç yoğunluğuna ulaşılmıştır. Yüksek güç yoğunluklarında (225 mW.cm-2) ise yakıtkullanım veriminin oldukça düştüğü (%30 verim) tespit edilmiştir.Öğe Neutronic performance of CANDU reactor fuelling with ThC2/(UC2)-U-233(WILEY-BLACKWELL, 2011) Yildiz, Kadir; Sahin, Necmettin; Alkan, MahmutU-233 isotope is used as a booster fissile fuel material in the form of mixed ThC2/(UC2)-U-233 fuel in a Canada Deuterium Uranium (CANDU) fuel bundle in order to assure the initial criticality at startup. Three different fuel compositions have been used: (1) 97% ThC2+3% (UC2)-U-233, (2) 98% ThC2+2% (UC2)-U-233 and (3) 99% ThC2+1% (UC2)-U-233. The temporal variation of the criticality k(infinity) and the burn-up values of the reactor have been calculated by full-power operation for a period of 20 years. The criticality starts by k(infinity) = 1.541, 1.355 and 0.995 for modes of (1), (2) and (3) fuel compositions, respectively. A sharp decrease in the criticality has been observed in the first 2 years as a consequence of rapid U-233 burnout fuelling with (1) and (2) modes. The criticality becomes quasi-constant after the second year and remains above k(infinity) similar to 1.06 for 20 years. After the second year, the CANDU reactor begins to operate practically as a thorium burner. Very high burnup could be achieved with the same fuel materials (up to 500 000 MW day t (1)), provided that the fuel rod claddings would be replaced periodically (after every 500 00 or 100 000 MW day t(-1)). The reactor criticality will be sufficient for fuelling with (1) and (2) modes until a great fraction of the thorium fuel is burnt up. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically. Copyright (C) 2010 John Wiley & Sons, Ltd.Öğe Sıcaklık ve deformasyon hızının şekillendirilebilmeye etkisinin deneysel ve teorik olarak incelenmesi(2008) Öztürk, Fahrettin; Alkan, Mahmut[Abstract Not Available]Öğe The Effects of the Different Tritium Breeding Materials to Fusil and Fisil Fuel Breeding in a ThSi2 Fuelled- Flibe Moderated Fusion-Fission Hybrid Reactor(Gazi Univ, 2007) Acir, Adem; Yildiz, Kadir; Alkan, Mahmut; Sahin, NecmettinIn this work, in a ThSi2 fuelled-flibe moderated fusion-fission reactor in the tritium breeding zones of the reactor are used four different Li compound, respectively, Li2TiO3, Li2ZrO3, Li4SiO4 and Li2O. D-T fusion reactions are used as a fusion neutron source which produces 14.1 MeV neutrons with averaged energy. Fusil and fissile fuel breeding rates, fission energy breeding rates and fission power production are investigated for Delta t=10 days during a reactor operation period in four years. In tritium breeding zones used Li2O of the reactor provided highest fusil breeding rate whereas, highest value of fissile breeding and production of the fission energy are reached with using of Li2TiO3 and Li2ZrO3 in tritium breeding zones of the blanket.Öğe Thermal Analysis of Chip on Board Packaging of High Power Led's with Heat Pipe Using Cfd for Street Lights(Gazi Univ, 2018) Cicek, Burcu; Sahin, Necmettin; Alkan, MahmutIn this study, in order to provide heat dissipation of the high power LEDs to be used for street illumination, U-shaped cylindrical copper heat pipes are used. Thermal analysis of this system was carried out numerically in the ANSYS Fluent software. Firstly, thermal analysis was performed for different numbers, diameters and lengths of heat pipes and optimum values were obtained. Afterwards, the optimum materials to be used as components of LED packages were determined. In addition, the effect of the power applied to the LED chip and of ambient temperature on the temperature distribution of the whole system was examined.Öğe Thermal analysis of chip on board packaging of high power led’s with heat pipe using Cfd for street lights(Gazi Universitesi, 2018) Cicek, Burcu; Sahin, Necmettin; Alkan, MahmutIn this study, in order to provide heat dissipation of the high power LEDs to be used for street illumination, U-shaped cylindrical copper heat pipes are used. Thermal analysis of this system was carried out numerically in the ANSYS Fluent software. Firstly, thermal analysis was performed for different numbers, diameters and lengths of heat pipes and optimum values were obtained. Afterwards, the optimum materials to be used as components of LED packages were determined. In addition, the effect of the power applied to the LED chip and of ambient temperature on the temperature distribution of the whole system was examined. © 2018, Gazi University Eti Mahallesi. All rights reserved.Öğe Thickness dependent yielding behavior and formability of AA6082-T6 alloy: experimental observation and modeling(Springer London Ltd, 2020) Cavusoglu, Onur; Surucu, Halit Ilhan; Toros, Serkan; Alkan, MahmutThis study analyzes thickness-dependent of the yielding behavior and forming limit diagrams (FLDs) of the AA6082-T6 aluminum alloy sheet. Mechanical behavior of the materials of 1 and 1.5 mm sheet thickness is observed having performed anisotropy and tensile tests at 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees to the rolling direction. By using Hill-48 and Barlat-89 yield criteria, r-value and yield stress relations were defined and yield loci were obtained. Forming limit diagrams were created using experimental data and Marciniak-Kuczynski (MK) model. It was observed that increased sheet thickness also increases anisotropy while decreasing yield stress; yield locus was found to be smaller. The formability of the material increased as the sheet thickness increases.
