Browsing by Author "Sahin, Suemer"
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Conference Object Citation Count: 33Criticality and burn up evolutions of the Fixed Bed Nuclear Reactor with alternative fuels(Pergamon-elsevier Science Ltd, 2010) Şahin, Sümer; Sahin, Haci Mehmet; Acir, Adem; Department of Mechanical EngineeringTime evolution of criticality and burn-up grades of the Fixed Bed Nuclear Reactor (FBNR) are investigated for alternative fuels. These are: (1) low enriched uranium, (2) weapon grade plutonium, (3) reactor grade plutonium, and (4) minor actinides in the spent fuel of light water reactors (LWRs). The criticality calculations are conducted with SCALE 5.1 using S(8)-P(3) approximation in 238 neutron energy groups with 90 groups in thermal energy region. The main results of the study can be summarized as follows: (1) Low enriched uranium (UO(2)): FBNR with an enrichment grade of 9% and 19% will start with k(eff) = 1.2744 and k(eff) = 1.36 and can operate similar to 8 and >15 years with the same fuel charge, where criticality drops to k(eff) = 1.06 and a burn-up grade of 54 000 and >110000 MW.D/t can be attained. (2) Weapon grade plutonium: Such a high quality nuclear fuel suggests to be mixed with thorium. Second series of criticality calculations are conducted with fuel compositions made of thoria (ThO(2)) and weapon grade PuO(2), where PuO(2) component has been varied from 1% to 100%. Criticality with k(eff) > 1.0 is achieved by similar to 2.5% PuO(2). At 4% PuO(2), the reactor criticality will become satisfactory (k(eff) = 1.1121), rapidly increasing with more PuO(2). A reasonable mixture will by around 20% PuO(2) and 80% ThO(2) with a k(eff) = 1.2864. This mixed fuel would allow full power reactor operation for >20 years and burn-up grade can reach 136 000 MW.D/t. (3) Reactor grade plutonium: Third series of criticality calculations are conducted with fuel compositions made of thoria and reactor grade PuO(2), where PuO(2) is varied from 1% to 100%. Reactor becomes critical by 8% PuO(2) content. One can achieve k(eff) = 1.2670 by 35% PuO(2) and would allow full power reactor operation also for >20 years and burn-up grade can reach 123 000 MW.D/t. (4) Minor actinides in the spent fuel of LWRs: Fourth series of criticality calculations are conducted with fuel compositions made of thoria and MAO(2), where MAO(2) is varied from 1% to 100%. Reactor becomes critical by similar to 17% MAO(2) content. Reasonably high reactor criticality (k(eff) = 1.2673) is achieved by 50% MAO(2) for a reactor operation time of 15 years with a burn up of 86 000 MW.D/t without fuel change. On that way, the hazardous nuclear waste product can be transmuted as well as utilized as fuel. (C) 2010 Elsevier Ltd. All rights reserved.Editorial Citation Count: 0SPECIAL ISSUE Energy Conversion and Management An International Journal(Pergamon-elsevier Science Ltd, 2010) Şahin, Sümer; Sahin, Suemer; Department of Mechanical Engineering[No Abstract Available]Article Citation Count: 24Utilization of TRISO fuel with reactor grade plutonium in CANDU reactors(Elsevier Science Sa, 2010) Şahin, Sümer; Sahin, Haci Mehmet; Acir, Adem; Department of Mechanical EngineeringLarge quantities of plutonium have been accumulated in the nuclear waste of civilian LWRs and CANDU reactors. Reactor grade plutonium and heavy water moderator can give a good combination with respect to neutron economy. On the other hand. TRISO type fuel can withstand very high fuel burn-up levels. The paper investigates the prospects of utilization of TRISO fuel made of reactor grade plutonium in CANDU reactors. TRISO fuels particles are imbedded body-centered cubic (BCC) in a graphite matrix with a volume fraction of 68%. The fuel compacts conform to the dimensions of CANDU fuel compacts are inserted in rods with zircolay cladding. In the first phase of investigations, five new mixed fuel have been selected for CANDU reactors composed of (1) 4% RG-PuO2+ 96% ThO2; CD 6% RG-PuO2 + 94% ThO2; (3) 10% RG-PuO2+ 90% ThO2; 20% RG-PuO2+ 80% ThO2; (5) 30% RG-PuO2 + 70% ThO2. Initial reactor criticality (k(infinity,0) values) for the modes (1), (2), (3), (4) and are calculated as 1.4294, 1.5035, 1.5678, 1.6249, and 1.6535, respectively. Corresponding operation lifetimes are similar to 0.65, 1.1, 1.9.3.5, and 4.8 years and with burn ups of 30000, 60000, 100000. 200000 and 290000 MW d/tonne, respectively. The higher initial plutonium charge is the higher burn ups can be achieved. In the second phase, a graphical-numerical power flattening procedure has been applied with radially variable mixed fuel composition in the fuel bundle. Mixed fuel fractions leading to quasi-constant power production are found in the 1st, 2nd. 3rd and 4th row to be as 100% PuO2, 80/20% PuO2/ThO2, 60/40% PuO2/ThO2, and 40/60% PuO2/ThO2, respectively. Higher plutonium amount in the flattened case increases reactor operation lifetime to >8 years and the burn up to 580 000 MW d/tonne. Power flattening in the bundle leads to higher power plant factor and quasi-uniform fuel utilization, reduces thermal and material stresses, and avoids local thermal peaks. Extended burn-up grade implies drastic reduction of the nuclear waste material per unit energy output for final waste disposal. (C) 2010 Elsevier BM. All rights reserved.