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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 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 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 and minor actinide burning in a thorium fusion breeder(PERGAMON-ELSEVIER SCIENCE LTD, 2002) Sahin, S; Sahin, HM; Sozen, A; Bayrak, MA neutronic analysis has been performed for a thorium fusion breeder with a special task of burning minor actinides Np-237, Am-241, Am-243 and Cm-244 and production of U-233, Pu-238, Am-242m and Cm-245 for spacecraft application. Pu-238 is an important radioisotopic energy source for spacecraft generators. As potential nuclear fuels in the foreseeable future, U-233, Am-242m and Cm-245 would allow one to build extremely compact space reactors. Natural lithium has been selected as the coolant medium for the nuclear heat transfer out of the fuel zone. Minor actinides out of 5 and 10 units of LWRs per metre of blanket height have been mixed with ThO2. Higher fission rates in minor actinides enables one to realise a power flattening in the fissile zone over three years of plant operation by a gradual increase in the radial direction at start-up. This has significant advantages with respect to plant operation over the long term and also with respect to a uniform utilisation of the nuclear fuel in the fissile zone. After three years of plant operation, the net U-233 production is similar to300 kg per metre of blanket height. The Pu-238 yield is 21 and 41 kg for a waste actinide charge out of 5 and 10 units of LWRs per metre of blanket height, respectively, and the Cm-245 yield is 1.1 and 2 kg, respectively. The net Am-242m production is practically nil. With waste actinides out of 10 reactor units per metre of blanket height, the flattening of the nuclear heat production density in the fissile zone is almost perfect. Waste actinides out of five reactor units per metre of blanket height allow still an excellent power flattening. The quasi-constant power shape is saved over 36 months. (C) 2002 Elsevier Science Ltd. All rights reserved.Öğe Radiation shielding mass saving for the magnet coils of the VISTA spacecraft(PERGAMON-ELSEVIER SCIENCE LTD, 1999) Sahin, S; Sahin, HMRadiation shielding structure of a design concept with inertial fusion energy propulsion for manned or heavy cargo deep space missions beyond earth orbit has been investigated. Fusion power deposited in the inertial confined fuel pellet debris delivers the rocket propulsion with the help of a magnetic nozzle. The nuclear heating in the super conducting magnet coils determines the radiation shielding mass of the spacecraft. It was possible to achieve considerable mass saving with respect to a recent design work, coupled with higher design limits for coil heating (up to 5 mW/cm(3)). The neutron and gamma-ray penetration into the coils is calculated using the SN methods with a high angular resolution in (r-z) geometry in S16P3 approximation by dividing the solid space angle in 160 sectors. Total peak nuclear heat generation density in the coils is calculated as 3.143 mW/cm(3) by a fusion power of 17 500 MW. Peak neutron heating density is 1.469 mW/cm(3) and peak gamma-ray heating density is 1.674 mW/cm(3). However, volume averaged heat generation in the coils is much lower, namely 74, 163 and 337 mu W/cm(3) for neutron, gamma-ray and total nuclear heating, respectively. The net mass of the radiation shielding for the magnet coils is 200 tonne by a total mass of 6000 tonne of the space craft. (C) 1999 Elsevier Science Ltd. All rights reserved.
