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Öğe An assessment of thorium and spent LWR-fuel utilization potential in CANDU reactors(PERGAMON-ELSEVIER SCIENCE LTD, 2004) Sahin, S; Sahin, HM; Alkan, M; Yildiz, KA neutronic analysis has been performed to assess a prospective utilization of light water reactor (LWR) spent fuel in Canada deuterium uranium (CANDU) reactors mixed with thoria (ThO2). The study is conducted for mixture grades with 50%, 60% and 100% LWR spent fuel and 50%, 40% and 0% thoria, respectively. Burn-up grades are evaluated for alternative fuels to reach a bundle criticality of k(infinity) = 1.06, which are calculated as similar to28,000, similar to14;000, similar to8000 and 8800 MW d/MT with 100%, 60% and 50% LWR spent fuel content and for natural uranium fuelled CANDU after plant operation periods of 690, 340, 200 and 205 days, respectively. The presence of even plutonium isotopes with higher neutron absorption cross sections in the LWR spent fuel obliges starting with a higher cumulative fissile inventory in the initial charge compared to natural uranium fuel. Extended utilization of worldwide disposed spent nuclear LWR fuel in CANDU reactors in a symbiotic system opens prospects with respect to environmental concerns as well as to energy economics. After separation of the fission products, further utilization of the actinides in nuclear waste becomes possible as a valuable nuclear fuel. (C) 2003 Elsevier Ltd. All rights reserved.Öğe An investigation of the effects of neutron energy-group structures and resonance treatment in a fusion-fission hybrid reactor fuelling with Tho(2)(PERGAMON-ELSEVIER SCIENCE LTD, 2005) Yildiz, KIn this work, the effects of neutron energy-group structures and resonance treatments on the main integral neutronic parameters are investigated in a fusion-fission hybrid reactor, which has a fast and a thermal blanket fuelling with ThO2. A D-T fusion neutron (14.1 MeV) is used as a neutron source. Fissile zone is cooled: (a) with light water for the moderated blanket and (b) with pressurized helium gas for the fast blanket. The neutronic parameters have been evaluated with and without a resonance treatment for the same blanket compositions for the sake of a consistent comparison. The study has shown that neutron reactions above a threshold energy in fast neutron groups are less sensitive to resonance treatment, such as Li-7(n,alphan')T and (232) Th(n,f). Neutron energy-group structures in the neutron libraries and description of fusion neutron source spectrum mainly affect these reactions. On the other hand, neutron reactions in the resonance and thermal energy groups are sensitive to resonance treatment, such as Li-6(n,alpha)T and Th-232(n,gamma), depending on the resonance structures. In the fast blanket calculations, resonance-based errors are lower and neutron source based errors are higher than in the moderated blanket. Furthermore, a correct description of the fusion neutron source spectrum over several neutron energy groups is essential to calculate fission reaction rates, fission heating density, fusile and fissile breeding rates and neutron leakage accurately. (C) 2004 Elsevier Ltd. All rights reserved.Öğe Effects of spectral shifting in an inertial confinement fusion system(CARL HANSER VERLAG, 2005) Sahin, S; Sahin, HM; Yildiz, K; Acir, AThe 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.Öğe Fissile fuel breeding with peaceful nuclear explosives(ELSEVIER SCIENCE SA, 2003) Sahin, S; Yalcin, S; Yildiz, KNeutron physics analysis of a dual purpose modified PACER concept has been conducted. A protective liquid droplet jet zone of 2 m thickness is considered as coolant, energy carrier, and fusile and fissile breeder. Flibe as the main constituent is mixed with increased mole-fractions of heavy metal salt (ThF4 and UF4) starting by 2 up to 12 mol.%. The neutronic model assumed a 30 m radius underground spherical geometry cavity with a 1 cm thick SS-304 stainless steel liner attached to the excavated rock wall. By a self-sufficient tritium breeding of 1.05 with 5 mol.% ThF4, or 9 mol.% UF4 an excess nuclear fuel breeding rate of 1900 kg/year of U-233 or 3000 kg/year Pu-239 of extremely high isotopic purity can be realized. This precious fuel can be considered for special applications, such as spacecraft reactors or other compact reactors. The heavy metal constituents in jet zone acts as an energy amplifier, leading to an energy multiplication of M = 1.27 or 1.65 for 5 mol.% ThF4, or 9 mol.% UF4, respectively. As an immediate result of the strong neutron attenuation in the jet zone, radiation damage with dpa < 1.4 and He < 7 ppm after a plant operation period of 30 years will be well below the damage limit values. The site could essentially be abandoned, or the cavity could be used as a shallow burial site for other qualified materials upon decommissioning. Finally, the totality of the site with all nuclear peripheral sections must be internationally safeguarded carefully, (C) 2003 Elsevier B.V. All rights reserved.Öğe Investigation of CANDU reactors as a thorium burner(Pergamon-Elsevier Science Ltd, 2006) Sahin, S; Yildiz, K; Sahin, HM; Acir, ALarge 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.Öğe Power flattening in the fuel bundle of a CANDU reactor(ELSEVIER SCIENCE SA, 2004) Sahin, S; Yildiz, K; Acir, AThe 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.
