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    Effects of spectral shifting in an inertial confinement fusion system
    (CARL HANSER VERLAG, 2005) Sahin, S; Sahin, HM; Yildiz, K; Acir, A
    The main objective is to study the effects of spectral shifting in an inertial confinement system for kT/shot energy regime on the breeding performance for tritium and for high quality fissile fuel. A protective liquid droplet jet zone of 2 m thickness is used as coolant, energy carrier and breeder Flibe as the main constituent is mixed with increased mole-fractions of heavy metal salt (ThF4 or UF4) starting by 2 moles% up to 12 moles%. Spectrum softening within the inertial confinement system reduces the tritium production ratio (TBR) in the protective coolant to a lower level than unity. However additional tritium production in the (Li2DT)-Li-6 zone of the system increases TBR to values above unity and allows a continuous operation of the power plant with a self-sustained fusion fuel supply. By modest fusion fuel burn efficiencies (40 to 60%) and with a few mol. % of heavy metal salt in the coolant in form of ThF4 or % UF4, a satisfactory TBR of > 1.05 can be realized. In addition to that, excess fissile fuel of extremely high isotopic purity with a rate of similar to 1000 kg/year of U-233 or Pu-239 can be produced. Radiation damage through atomic displacements and helium gas production after a plant operation period of 30 years is very low, namely dpa <1 and He < 2 ppm, respectively.
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    Investigation of CANDU reactors as a thorium burner
    (Pergamon-Elsevier Science Ltd, 2006) Sahin, S; Yildiz, K; Sahin, HM; Acir, A
    Large quantities of plutonium have been accumulated in the nuclear waste of civilian LWRs and CANDU reactors. Reactor grade plutonium can be used as a booster fissile fuel material in the form of mixed ThO2/PuO2 fuel in a CANDU fuel bundle in order to assure reactor criticality. The paper investigates the prospects of exploiting the rich world thorium reserves in CANDU reactors. Two different fuel compositions have been selected for investigations: (1) 96% thoria (ThO2) + 4% PuO2 and (2) 91% ThO2 + 5% UO2 + 4% PuO2. The latter is used for the purpose of denaturing the new U-233 fuel with U-238. The behavior of the reactor criticality k(infinity) and the burn-up values of the reactor have been pursued by full power operation for >similar to 8 years. The reactor starts with k(infinity) = -1.39 and decreases asymptotically to values of k(infinity) > 1.06, which is still tolerable and useable in a CANDU reactor. The reactor criticality k(infinity) remains nearly constant between the 4th year and the 7th year of plant operation, and then, a slight increase is observed thereafter, along with a continuous depletion of the thorium fuel. After the 2nd year, the CANDU reactor begins to operate practically as a thorium burner. Very high burn-up can be achieved with the same fuel (> 160,000 MW D/MT). The reactor criticality would be sufficient until a great fraction of the thorium fuel is burned up, provided that the fuel rods could be fabricated to withstand such high burn-up levels. Fuel fabrication costs and nuclear waste mass for final disposal per unit energy could be reduced drastically. (c) 2005 Elsevier Ltd. All rights reserved.
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    Power flattening in the fuel bundle of a CANDU reactor
    (ELSEVIER SCIENCE SA, 2004) Sahin, S; Yildiz, K; Acir, A
    The strong non-uniformity of the fission power production density in the CANDU fuel bundle could have been mitigated to a great degree. A satisfactory power flattening has been achieved through an appropriately evaluated method by varying the composition of the LWR spent fuel/ThO2 Mixture in a CANDU fuel bundle in radial direction and keeping fuel rod dimensions unchanged. This will help also to greatly simplify fuel rod fabrication and allow a higher degree of quality assurance standardization. Three different bundle fuel charges are investigated: (1) the reference case, uniformly fueled with natural UO2, (2) a bundle uniformly fueled with LWR spent fuel, and (3) a bundle fueled with variable mixed fuel composition in radial direction leading to a flat power profile (100% LWR spent fuel in the central rod, 80% LWR + 20% ThO2 in the second row, 60% LWR + 40% ThO2 in the third row and finally 40% LWR + 60% ThO2 in the peripheral fourth row). Burn-up grades for these three different bundle types are calculated as similar to7700, similar to27,300, and 10,000 MW.D/MT until reaching a lowest bundle criticality limit of k(infinity) = 1.06. The corresponding plant operation periods are 170, 660, and 240 days, respectively. (C) 2004 Elsevier B.V. All rights reserved.
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    The neutron production cross sections for Pb, Bi, and Au targets and neutron multiplicity for nuclear spallation reaction induced by 20-to 1600-MeV protons
    (AMER NUCLEAR SOCIETY, 2004) Demirkol, I; Tel, E; Arasoglu, A; Ozmen, A; Sarer, B; Acir, A; Alkan, M
    Various cross sections of the (p + Pb-206,Pb-207,Pb-208), (p + Pb-nat), (p + Bi-209), and (p + Au-197) reactions have been calculated at energies between 20 and 1600 MeV using the Cascade-Exciton model, Geometry-Dependent Hybrid model, and Hybrid model. The neutron multiplicity has been predicted. The calculated results have been compared with the experimental data taken from the literature. The accordance of the calculated results with the experimental data has been examined.