Browsing by Author "Acir, Adem"
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Article Citation Count: 10Commercial utilization of weapon grade plutonium as TRISO fuel in conventional CANDU reactors(Pergamon-elsevier Science Ltd, 2012) Şahin, Sümer; Sahin, Haci Mehmet; Acir, Adem; Department of Mechanical EngineeringLarge quantities of weapon grade (WG) plutonium have been accumulated in the nuclear warheads. Plutonium and heavy water moderator can give a good combination with respect to neutron economy. TRISO type fuel can withstand very high fuel burn up levels. The paper investigates the prospects of utilization of TRISO fuel made of WG-plutonium in CANDU reactors. Three different fuel compositions have been investigated: (1): 90% ThC + 10% PuC, (2): 70% ThC + 30% PuC and (3): 50% ThC + 50% PuC. The temporal variation of the criticality k(infinity) and the burn-up values of the reactor have been calculated by full power operation up to 17 years. Calculated startup criticalities for these fuel modes are k(infinity.0)= 1.6403, 1.7228 and 1.7662, respectively. Attainable burn up values and reactor operation times without new fuel charge will be 94700, 265000 and 425000 MW.D/MT and along with continuous operation periods of similar to 3.5, 10 and 17 years, respectively, for the corresponding modes. These high burn ups would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically. (C) 2012 Elsevier Ltd. All rights reserved.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.Article Citation Count: 0Derivation of empirical equations for neutronic performance in a thorium fusion breeder with various coolants using regression analysis(Pergamon-elsevier Science Ltd, 2011) Alakoç, Nilüfer Pekin; Alakoc, Nilufer Pekin; Industrial EngineeringIn this paper, regression analyses (RA) are presented for the neutronic calculation of ThO2 mixed (CmO2)-Cm-244 fuel with different neutronic parameters for various coolants, natural lithium, Li20Sn80 and Flinabe, respectively. The tritium breeding ratio (TBR), energy multiplication factor (M), total fission rate (Xi) and Th-232(n, gamma) reaction is computed by XSDRNPM. In addition, this numerical results are estimated by RA depends on neutronic parameters and the empirical equations for neutronic performance are acquired. The results obtained by using XSDRNPM and the results of the RA, obtained empirical equations, are compared. The empirical equations indicate that RA can successfully be used for the prediction of the neutronic performance parameters in the hybrid reactor with a high degree of accuracy. In addition, correlation matrix is calculated to determined statistical relationships between variables TBR, M, Sigma(f), and Th-232(n, gamma). (C) 2011 Elsevier Ltd. All rights reserved.Article Citation Count: 21LIFE hybrid reactor as reactor grade plutonium burner(Pergamon-elsevier Science Ltd, 2012) Şahin, Sümer; Sahin, Haci Mehmet; Acir, Adem; Department of Mechanical EngineeringThe early version of the conceptual modified design of the Laser Inertial Confinement Fusion Fission Energy (LIFE) engine consists of a spherical fusion chamber of 5 m diameter, surrounded by a multi-layered blanket. The first wall is made of 2 cm thick ODS and followed by a Li17Pb83 zone (2 cm), acting as neutron multiplier, tritium breeding and front coolant zone. It is separated by an ODS layer (2 cm) from the FLIBE molten salt zone (50 cm), containing fissionable fuel. A 3rd ODS layer (2 cm) separates the molten salt zone on the right side from the graphite reflector (30 cm). Calculations have been conducted for a constant fusion driver power of 500 MWth, in S-8-P-3 approximation using 238-neutron groups. Reactor grade (RG) plutonium carbide fuel in form of TRISO particles with volume fractions of 2%, 3%, 4%, 5% and 6% have been dispersed homogenously in the FLIBE coolant. Tritium breeding ratio (TBR) values per incident fusion neutron for the above cited cases start with TBR = 1.35, 1.52, 1.73, 2.02 and 2.47, respectively. With the depletion of fissionable RG-Pu isotopes, TBR decreases gradually. At startup, higher fissionable fuel content in the molten salt leads to higher blanket energy multiplication, namely M-0 = 3.8, 5.5, 7.7, 10.8 and 15.4 with 2%, 3%, 4%, 5% and 6% TRISO volume fraction, respectively. Calculations have led to very high burn up values (>400,000 MD.D/MT). TRISO particles can withstand such high burn ups. Such high burn ups would lead to drastic reduction of final nuclear waste per unit energy production. (C) 2012 Elsevier Ltd. All rights reserved.Conference Object Citation Count: 5REDUCTION OF WEAPON GRADE PLUTONIUM INVENTORIES IN A THORIUM BURNER(Amer Nuclear Soc, 2012) Şahin, Sümer; Sahin, Haci Mehmet; Acir, Adem; Department of Mechanical EngineeringLarge quantities of weapon grade (WG) plutonium have been accumulated in the nuclear warheads. Plutonium and heavy water moderator can give a good combination with respect to neutron economy. TRISO type fuel can withstand very high fuel burn up levels. The paper investigates the prospects of utilization of TRISO fuel made of WG-plutonium in CANDU reactors. Three different fuel compositions have been investigated: (1): 90 % ThC + 10 % PuC, (2): 70 % ThC + 30 % PziC and (3): 50 ThC + 50 % PuC. The temporal variation of the criticality k(infinity) and the burn-up values of the reactor have been calculated by full power operation up to 17 years. Calculated startup criticalities for these fuel modes are k(infinity),(0) = 1.6403, 1.7228, 1.7662, respectively. Attainable burn up values and reactor operation times with the same fuel charge will be 94 700, 265 000, 425 000 MW.D/MT and similar to 3.5, 10, 17 years, respectively. These high burn ups would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically.Conference Object Citation Count: 7UTILIZATION OF REACTOR GRADE PLUTONIUM AS ENERGY MULTIPLIER IN THE LIFE ENGINE(Amer Nuclear Soc, 2012) Şahin, Sümer; Sahin, Haci Mehmet; Acir, Adem; Department of Mechanical EngineeringThe accumulated reactor grade (RG)-plutonium as nuclear waste of conventional reactors is estimated to exceed 1700 tonnes. Laser Inertial Confinement Fusion Fission Energy (LIFE) engine is considered to incinerate RG-plutonium in stockpiles. Calculations have been conducted for a constant fusion driver power of 500 MWth in S-8-P-3 approximation using 238-neutron groups. RG-plutonium out of the nuclear waste of LWRs is used in form of fissile carbide fuel in TRISO particles with volume fractions of 2, 3, 4, 5 and 6 %, homogenously dispersed in the Flibe coolant. Respective tritium breeding ratio (TBR) values per incident fits ion neutron are calculated as TBR = 1.35, 1.52, 1.73, 2.02 and 2.47 at start-up. With the burn up of fissionable RG-Pu isotopes in the coolant, TBR decreases gradually. Similarly, blanket energy multiplications are calculated as M-0 = 3.8, 5.5, 7.7, 10.8 and 15.4 at start-up, respectively. Calculations have indicated prospects of achievability of very high burn up values (> 400 000 MD.D/MT).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.