The Experts below are selected from a list of 1626 Experts worldwide ranked by ideXlab platform
Seiichi Koshizuka - One of the best experts on this subject based on the ideXlab platform.
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core design of a high temperature fast reactor cooled by supercritical light water
Annals of Nuclear Energy, 1999Co-Authors: Tami Mukohara, Seiichi Koshizuka, Yoshiaki OkaAbstract:Abstract A high-temperature large fast reactor cooled by supercritical water (SCFR-H) is designed for assessing its technical feasibility and potential economical improvement. The coolant system is once-through, direct cycle where whole core coolant flows to the turbine. The goal is to achieve the high coolant outlet temperature over 500°C. We study the reactors with blankets cooled by ascending and descending flow. SCFR-H adopts a radial heterogeneous core with Zirconium-Hydride layers between the driver core and the blankets for making coolant void reactivity negative. The coolant outlet temperature of the core with blankets cooled by ascending flow is low, 467°C. The reasons are as follows: (1) the power swing due to the accumulation of fissile material in the inner blankets with burn-up, and (2) local power peak in the assemblies due to the Zirconium-Hydride layers. The difference in the outlet coolant temperature is more enhanced than the low temperature core where outlet temperature is approximately 400°C. The reason is that the coolant temperature is more sensitive to the enthalpy change than near the pseudo critical temperature, 385°C at 25 MPa. Thus, we design the core with blankets cooled by descending flow to obtain high coolant outlet temperature. The coolant outlet temperature becomes 537°C, which is 70°C higher than that of the core with ascending blanket flow. The thermal efficiency is improved from 43.2 to 44.6%. The coolant mass flow rate per electric power decreases by 14%. This will reduce the size of the balance of plant (BOP) system. The power of the reactor is high (1565 MWe) and the void reactivity is negative.
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systems design of direct cycle supercritical water cooled fast reactors
Nuclear Technology, 1995Co-Authors: Seiichi Koshizuka, Tatjana Jevremovic, Yashushi OkanoAbstract:The system design of a direct-cycle supercritical-water-cooled fast reactor is presented. The supercritical water does not exhibit a change of phase. the recirculation system, steam separator, and dryer of a boiling water reactor (BWR) are unnecessary. Roughly speaking, the reactor pressure vessel and control rods are similar to those of a pressurized water reactor, the containment and emergency core cooling system are similar to a BWR, and the balance of plant is similar to a supercritical-pressure fossil-fired power plant (FPP). the electric power of the fast converter is 1,508 MW(electric). The number of coolant loops is only two because of the high coolant enthalpy. Containment volume is much reduced. The thermal efficiency is improved 24% over a BWR. The coolant void reactivity is negative by placing thin Zirconium-Hydride layers between seeds and blankets. The power costs would be much reduced compared with those of a light water reactor (LWR) and a liquid-metal fast breeder reactor. The concept is based on the huge amount of experience with the water coolant technology of LWRs and FPPs. The oxidation of stainless steel cladding is avoided by adopting a much lower coolant temperature than that of the FPP.
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core design of a direct cycle supercritical water cooled fast breeder reactor
Nuclear Technology, 1994Co-Authors: Tatjana Jevremovic, Yoshiaki Oka, Seiichi KoshizukaAbstract:The conceptual design of a direct-cycle fast breeder reactor (FBR) core cooled by supercritical water is carried out as a step toward a low-cost FBR plant. The supercritical water does not exhibit change of phase. The turbines are directly driven by the core outlet coolant. In comparison with a boiling water reactor (BWR), the recirculation systems, steam separators, and dryers are eliminated. The reactor system is much simpler than the conventional steam-cooled FBRs, which adopted Loeffler boilers and complicated coolant loops for generating steam and separating it from water. Negative complete and partial coolant void reactivity are provided without much deterioration in the breeding performances by inserting thin Zirconium-Hydride layers between the seeds and blankets in a radially heterogeneous core. The net electric power is 1245 MW (electric). The estimated compound system doubling time is 25 yr. The discharge burnup is 77.7 GWd/t, and the refueling period is 15 months with a 73% load factor. The thermal efficiency is high (41.5%), an improvement of 24% relative to a BWR's. The pressure vessel is not thick at 30.3 cm.
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effect of Zirconium Hydride layers on reducing coolant void reactivity of steam cooled fast breeder reactors
Journal of Nuclear Science and Technology, 1993Co-Authors: Tatjana Jevremovic, Yoshiaki Oka, Seiichi KoshizukaAbstract:The introduction of Zirconium-Hydride (ZrH1.7) layer between the seed and blanket is very effective in reducing the coolant-void reactivity of steam-cooled FBR. The void reactivity reduction is attributed to the rapid increase of neutron absorption and to the decrease of neutron production in the blanket due to the moderation through the layer. The reason is that the neutron multiplication factor decreases, reflecting the neutron balance of the whole core. It is effective even the layer thickness is 1 or 2 cm. Compared with the conventional uniform introduction of this moderator into the seed, the fixed layer concept is more effective in reducing void reactivity and hardly deteriorate the breeding ratio. The negative void reactivity is proved for the non-flat large-sized radial heterogeneous core where the layers are placed between the seeds and blankets. The neutron absorption rate increases, the fast fission rate decreases in the central, inner and radial blankets.
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conceptual design of an indirect cycle supercritical steam cooled fast breeder reactor with negative coolant void reactivity characteristics
Annals of Nuclear Energy, 1993Co-Authors: Tatjana Jevremovic, Yoshiaki Oka, Seiichi KoshizukaAbstract:Abstract Conceptual design of a large-sized FBR cooled by supercritical steam is a step towards low-cost FBR plants. Negative complete and partial coolant void reactivity is proved, without much deterioration in the breeding performance, by our novel concept of inserting thin Zirconium-Hydride layers between the seeds and blankets. A radially heterogeneous core is adopted. The net electric power is 1180 MWe. The estimated equilibrium compound system doubling time is 27 years. The discharge burnup is 70.0 GWd/t and the refueling period is 1 year with a 70% load factor. The reactor system is simple compared with a conventional steam-cooled FBR. The water-steam separation is unnecessary due to the supercritical water cooling. The thermal efficiency is high (39.6%), a relative improvement of 15% over PWRs. The pumping power is decreased due to the high coolant density. The pressure vessel is not very thick, 34.2 cm.
Tatjana Jevremovic - One of the best experts on this subject based on the ideXlab platform.
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negative coolant void reactivity in large fast breeder reactors with hydrogenous moderator layer
Annals of Nuclear Energy, 1996Co-Authors: Yoshiaki Oka, Tatjana JevremovicAbstract:Abstract Placing a thin Zirconium-Hydride (ZrH1.7) layer between seed and blanket is very effective in reducing the coolant-void reactivity of water-cooled and liquid-metal-cooled fast reactors. The fast neutrons which are generated in the seeds at voiding are moderated through the layer. In the blanket the neutron absorption increases and fast fission decreases. The total neutron balance becomes negative at voiding. It is effective even when the layer thickness is 1 or 2 cm. Compared with the conventional homogeneous introduction of the moderator in a seed, the breeding ratio is not much reduced due to the locality of the moderation. The negative void reactivity is proved for the non-flat, large-sized radial heterogeneous cores where the layers are placed between seeds and blankets.
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systems design of direct cycle supercritical water cooled fast reactors
Nuclear Technology, 1995Co-Authors: Seiichi Koshizuka, Tatjana Jevremovic, Yashushi OkanoAbstract:The system design of a direct-cycle supercritical-water-cooled fast reactor is presented. The supercritical water does not exhibit a change of phase. the recirculation system, steam separator, and dryer of a boiling water reactor (BWR) are unnecessary. Roughly speaking, the reactor pressure vessel and control rods are similar to those of a pressurized water reactor, the containment and emergency core cooling system are similar to a BWR, and the balance of plant is similar to a supercritical-pressure fossil-fired power plant (FPP). the electric power of the fast converter is 1,508 MW(electric). The number of coolant loops is only two because of the high coolant enthalpy. Containment volume is much reduced. The thermal efficiency is improved 24% over a BWR. The coolant void reactivity is negative by placing thin Zirconium-Hydride layers between seeds and blankets. The power costs would be much reduced compared with those of a light water reactor (LWR) and a liquid-metal fast breeder reactor. The concept is based on the huge amount of experience with the water coolant technology of LWRs and FPPs. The oxidation of stainless steel cladding is avoided by adopting a much lower coolant temperature than that of the FPP.
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core design of a direct cycle supercritical water cooled fast breeder reactor
Nuclear Technology, 1994Co-Authors: Tatjana Jevremovic, Yoshiaki Oka, Seiichi KoshizukaAbstract:The conceptual design of a direct-cycle fast breeder reactor (FBR) core cooled by supercritical water is carried out as a step toward a low-cost FBR plant. The supercritical water does not exhibit change of phase. The turbines are directly driven by the core outlet coolant. In comparison with a boiling water reactor (BWR), the recirculation systems, steam separators, and dryers are eliminated. The reactor system is much simpler than the conventional steam-cooled FBRs, which adopted Loeffler boilers and complicated coolant loops for generating steam and separating it from water. Negative complete and partial coolant void reactivity are provided without much deterioration in the breeding performances by inserting thin Zirconium-Hydride layers between the seeds and blankets in a radially heterogeneous core. The net electric power is 1245 MW (electric). The estimated compound system doubling time is 25 yr. The discharge burnup is 77.7 GWd/t, and the refueling period is 15 months with a 73% load factor. The thermal efficiency is high (41.5%), an improvement of 24% relative to a BWR's. The pressure vessel is not thick at 30.3 cm.
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effect of Zirconium Hydride layers on reducing coolant void reactivity of steam cooled fast breeder reactors
Journal of Nuclear Science and Technology, 1993Co-Authors: Tatjana Jevremovic, Yoshiaki Oka, Seiichi KoshizukaAbstract:The introduction of Zirconium-Hydride (ZrH1.7) layer between the seed and blanket is very effective in reducing the coolant-void reactivity of steam-cooled FBR. The void reactivity reduction is attributed to the rapid increase of neutron absorption and to the decrease of neutron production in the blanket due to the moderation through the layer. The reason is that the neutron multiplication factor decreases, reflecting the neutron balance of the whole core. It is effective even the layer thickness is 1 or 2 cm. Compared with the conventional uniform introduction of this moderator into the seed, the fixed layer concept is more effective in reducing void reactivity and hardly deteriorate the breeding ratio. The negative void reactivity is proved for the non-flat large-sized radial heterogeneous core where the layers are placed between the seeds and blankets. The neutron absorption rate increases, the fast fission rate decreases in the central, inner and radial blankets.
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conceptual design of an indirect cycle supercritical steam cooled fast breeder reactor with negative coolant void reactivity characteristics
Annals of Nuclear Energy, 1993Co-Authors: Tatjana Jevremovic, Yoshiaki Oka, Seiichi KoshizukaAbstract:Abstract Conceptual design of a large-sized FBR cooled by supercritical steam is a step towards low-cost FBR plants. Negative complete and partial coolant void reactivity is proved, without much deterioration in the breeding performance, by our novel concept of inserting thin Zirconium-Hydride layers between the seeds and blankets. A radially heterogeneous core is adopted. The net electric power is 1180 MWe. The estimated equilibrium compound system doubling time is 27 years. The discharge burnup is 70.0 GWd/t and the refueling period is 1 year with a 70% load factor. The reactor system is simple compared with a conventional steam-cooled FBR. The water-steam separation is unnecessary due to the supercritical water cooling. The thermal efficiency is high (39.6%), a relative improvement of 15% over PWRs. The pumping power is decreased due to the high coolant density. The pressure vessel is not very thick, 34.2 cm.
J D Almer - One of the best experts on this subject based on the ideXlab platform.
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elastic strain tensor of Zirconium Hydrides in zr2 5 nb pressure tubes by synchrotron x ray diffraction
Journal of Applied Crystallography, 2019Co-Authors: Vicente Alvarez, J R Santisteban, G Domizzi, John S Okasinski, J D AlmerAbstract:Zirconium alloys are used in fuel cladding and structural components of nuclear power plants. Hydrogen enters the Zr matrix during plant operation and precipitates as Hydride particles that degrade the mechanical properties of the alloy, limiting service life. Knowledge of the stress state within Hydride precipitates is important to understand stress-induced degradation mechanisms such as delayed Hydride cracking, but no direct quantification has yet been reported in the literature. Here, measurements are reported of the average elastic strain tensor within δ Zirconium Hydride precipitates in Zr2.5%Nb pressure tube material from CANDU power plants. Complete intensity and strain pole figures for the Hydride were obtained by synchrotron X-ray diffraction experiments on specimens with hydrogen contents ranging from ∼100 wt p.p.m. hydrogen to nearly 100% δ-Hydride. Zirconium Hydride precipitates by a process involving a martensitic transformation, with two Hydride variants possible from a single α-Zr grain. A synthetic model of the Hydride crystallographic texture allowed the interpretation of the measured strain pole figures and quantification of the elastic strain tensor for both texture components. It was found that the two variants appear in nearly equal proportion but with different stress states, differing in the sign of the shear strain components (∼±3000 µ∊). This difference is possibly associated with the shear movement of Zr atoms during the phase transformation. This suggests that Hydride clusters are composed of stacks of smaller Hydrides in alternating Hydride variants. Stresses were estimated from a set of rather uncertain Hydride elastic constants. Overall, both variants showed compressive strains along the tube axial direction (∼5000 µ∊). For low hydrogen concentrations, the Hydrides' stress tensor is dominated by compressive stresses of ∼300 MPa along the axial direction, probably caused by the elongated morphology of Hydride clusters along this direction, and variant-dependent shear stresses of ∼±100 MPa, probably from the shear movement of the Zr atoms involved in the phase transformation.
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effect of crystallite orientation and external stress on Hydride precipitation and dissolution in zr2 5 nb
Journal of Nuclear Materials, 2014Co-Authors: P Vizcaino, M Vicente A Alvarez, J R Santisteban, A D Banchik, J D AlmerAbstract:Abstract Thermal cycling of Zr2.5%Nb pressure tubes specimens containing ∼100 wt ppm H between room temperature and 400 °C produces the dissolution and re-precipitation of Zirconium Hydride, with a distinctive hysteresis between these two processes. In this work, we have found that the details of the precipitation and dissolution depend on the actual orientation of the α-Zr grains where Hydride precipitation takes place. In situ synchrotron X-ray diffraction experiments during such thermal cycles have provided information about Hydride precipitation specific to the two most important groups of α-Zr phase orientations, namely crystallites having c -axes parallel ( m Hoop ) and tilted by ∼20° ( m Tilted ) from the tube hoop direction. The results indicate that Hydrides precipitate at slightly higher temperatures (∼5 °C), and dissolve at consistently higher temperatures (∼15 °C) in m Tilted grains than in m Hoop grains. Moreover, application of a tensile stress along the tube hoop direction results in two noticeable effects in Hydride precipitation. Firstly, it shifts Hydride precipitation towards higher temperatures, at a rate of ∼(0.08 ± 0.02) °C/MPa for Hydrides precipitated in the m Hoop grains. Secondly, it produces a redistribution of hydrogen between grains of different orientations, increasing Hydride precipitation on those α-Zr grains having their c -axes stretched by the external load. A detailed analysis of the diffracted signal shows that such redistribution occurs during the precipitation stage, as a result of changes in the precipitation temperatures for different grain orientations.
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the role of chemical free energy and elastic strain in the nucleation of Zirconium Hydride
Journal of Nuclear Materials, 2013Co-Authors: A T W Barrow, J D Almer, Caroline Toffolonmasclet, M R DaymondAbstract:Abstract In this work a combination of synchrotron X-ray diffraction and thermodynamic modelling has been used to study the dissolution and precipitation of Zirconium Hydride in α-Zr establishing the role of elastic misfit strain and chemical free energy in the α → α + δ phase transformation. The nucleation of Zirconium Hydride is dominated by the chemical free energy where the chemical driving force for Hydride precipitation is proportional to the terminal-solid solubility for precipitation and can be predicted by a function that is analogous to the universal nucleation parameter for the bainite transformation in ferrous alloys. The terminal-solid solubility for precipitation was found to be kinetically limited ⩾287 °C at a cooling rate of 5 °C min−1 or greater. The terminal solubilities were established using an offset method applied to the lattice strain data where a resolution of ∼10 wppm H can be achieved in the 〈c〉-direction. This is aided by the introduction of intra-granular strains in the 〈c〉-direction during cooling as a result of the thermal expansion anisotropy which increases the anisotropy associated with the misfitting H atoms within the α-Zr lattice.
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phase and texture analysis of a Hydride blister in a zr 2 5 nb tube by synchrotron x ray diffraction
Acta Materialia, 2011Co-Authors: M Vicente A Alvarez, G Domizzi, J R Santisteban, J D AlmerAbstract:This paper presents a detailed phase and texture study within and around a Hydride blister grown on the surface of a Zr-2.5%Nb pressure tube. The analysis is based on synchrotron X-ray diffraction experiments using an 80 keV photon beam and a high-speed area detector placed in transmission geometry. It was found that the blister is composed of two main phases, {alpha}-Zr and {delta}-ZrH, with a composition which changes locally across the blister. No location within the blister presents pure {delta} Zirconium Hydride, with a maximum of 80% for the volume fraction of {delta} Hydride at the center of the blister. The texture observed for both phases in the original pressure tube remains essentially unaltered across the Hydride blister. A detailed analysis of this texture using well-known parent-precipitate relationships shows that some selective precipitation occurs at {alpha}-Zr grains with their c-axis under a tensile stress, and on grains with grain boundaries favorably aligned for Hydride nucleation.
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strain evolution of Zirconium Hydride embedded in a zircaloy 2 matrix
Journal of Nuclear Materials, 2008Co-Authors: M Kerr, M R Daymond, R A Holt, J D AlmerAbstract:In situ synchrotron X-ray diffraction has been used to determine strain evolution in a minority phase, Zirconium Hydride, embedded in Zircaloy-2 (<100 wt ppm average hydrogen content). The elastic modulus of the Hydride is similar to that of Zircaloy-2. Three regimes are observed: I - elastic, II - post-yield load transfer from Zircaloy-2 to Hydride, and III - strain saturation, possibly due to Hydride fracture. The interpretation is supported by finite element calculations and scanning electron microscopy of the fracture surface.
Yoshiaki Oka - One of the best experts on this subject based on the ideXlab platform.
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core design of a high temperature fast reactor cooled by supercritical light water
Annals of Nuclear Energy, 1999Co-Authors: Tami Mukohara, Seiichi Koshizuka, Yoshiaki OkaAbstract:Abstract A high-temperature large fast reactor cooled by supercritical water (SCFR-H) is designed for assessing its technical feasibility and potential economical improvement. The coolant system is once-through, direct cycle where whole core coolant flows to the turbine. The goal is to achieve the high coolant outlet temperature over 500°C. We study the reactors with blankets cooled by ascending and descending flow. SCFR-H adopts a radial heterogeneous core with Zirconium-Hydride layers between the driver core and the blankets for making coolant void reactivity negative. The coolant outlet temperature of the core with blankets cooled by ascending flow is low, 467°C. The reasons are as follows: (1) the power swing due to the accumulation of fissile material in the inner blankets with burn-up, and (2) local power peak in the assemblies due to the Zirconium-Hydride layers. The difference in the outlet coolant temperature is more enhanced than the low temperature core where outlet temperature is approximately 400°C. The reason is that the coolant temperature is more sensitive to the enthalpy change than near the pseudo critical temperature, 385°C at 25 MPa. Thus, we design the core with blankets cooled by descending flow to obtain high coolant outlet temperature. The coolant outlet temperature becomes 537°C, which is 70°C higher than that of the core with ascending blanket flow. The thermal efficiency is improved from 43.2 to 44.6%. The coolant mass flow rate per electric power decreases by 14%. This will reduce the size of the balance of plant (BOP) system. The power of the reactor is high (1565 MWe) and the void reactivity is negative.
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negative coolant void reactivity in large fast breeder reactors with hydrogenous moderator layer
Annals of Nuclear Energy, 1996Co-Authors: Yoshiaki Oka, Tatjana JevremovicAbstract:Abstract Placing a thin Zirconium-Hydride (ZrH1.7) layer between seed and blanket is very effective in reducing the coolant-void reactivity of water-cooled and liquid-metal-cooled fast reactors. The fast neutrons which are generated in the seeds at voiding are moderated through the layer. In the blanket the neutron absorption increases and fast fission decreases. The total neutron balance becomes negative at voiding. It is effective even when the layer thickness is 1 or 2 cm. Compared with the conventional homogeneous introduction of the moderator in a seed, the breeding ratio is not much reduced due to the locality of the moderation. The negative void reactivity is proved for the non-flat, large-sized radial heterogeneous cores where the layers are placed between seeds and blankets.
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core design of a direct cycle supercritical water cooled fast breeder reactor
Nuclear Technology, 1994Co-Authors: Tatjana Jevremovic, Yoshiaki Oka, Seiichi KoshizukaAbstract:The conceptual design of a direct-cycle fast breeder reactor (FBR) core cooled by supercritical water is carried out as a step toward a low-cost FBR plant. The supercritical water does not exhibit change of phase. The turbines are directly driven by the core outlet coolant. In comparison with a boiling water reactor (BWR), the recirculation systems, steam separators, and dryers are eliminated. The reactor system is much simpler than the conventional steam-cooled FBRs, which adopted Loeffler boilers and complicated coolant loops for generating steam and separating it from water. Negative complete and partial coolant void reactivity are provided without much deterioration in the breeding performances by inserting thin Zirconium-Hydride layers between the seeds and blankets in a radially heterogeneous core. The net electric power is 1245 MW (electric). The estimated compound system doubling time is 25 yr. The discharge burnup is 77.7 GWd/t, and the refueling period is 15 months with a 73% load factor. The thermal efficiency is high (41.5%), an improvement of 24% relative to a BWR's. The pressure vessel is not thick at 30.3 cm.
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effect of Zirconium Hydride layers on reducing coolant void reactivity of steam cooled fast breeder reactors
Journal of Nuclear Science and Technology, 1993Co-Authors: Tatjana Jevremovic, Yoshiaki Oka, Seiichi KoshizukaAbstract:The introduction of Zirconium-Hydride (ZrH1.7) layer between the seed and blanket is very effective in reducing the coolant-void reactivity of steam-cooled FBR. The void reactivity reduction is attributed to the rapid increase of neutron absorption and to the decrease of neutron production in the blanket due to the moderation through the layer. The reason is that the neutron multiplication factor decreases, reflecting the neutron balance of the whole core. It is effective even the layer thickness is 1 or 2 cm. Compared with the conventional uniform introduction of this moderator into the seed, the fixed layer concept is more effective in reducing void reactivity and hardly deteriorate the breeding ratio. The negative void reactivity is proved for the non-flat large-sized radial heterogeneous core where the layers are placed between the seeds and blankets. The neutron absorption rate increases, the fast fission rate decreases in the central, inner and radial blankets.
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conceptual design of an indirect cycle supercritical steam cooled fast breeder reactor with negative coolant void reactivity characteristics
Annals of Nuclear Energy, 1993Co-Authors: Tatjana Jevremovic, Yoshiaki Oka, Seiichi KoshizukaAbstract:Abstract Conceptual design of a large-sized FBR cooled by supercritical steam is a step towards low-cost FBR plants. Negative complete and partial coolant void reactivity is proved, without much deterioration in the breeding performance, by our novel concept of inserting thin Zirconium-Hydride layers between the seeds and blankets. A radially heterogeneous core is adopted. The net electric power is 1180 MWe. The estimated equilibrium compound system doubling time is 27 years. The discharge burnup is 70.0 GWd/t and the refueling period is 1 year with a 70% load factor. The reactor system is simple compared with a conventional steam-cooled FBR. The water-steam separation is unnecessary due to the supercritical water cooling. The thermal efficiency is high (39.6%), a relative improvement of 15% over PWRs. The pumping power is decreased due to the high coolant density. The pressure vessel is not very thick, 34.2 cm.
Jean-marie Basset - One of the best experts on this subject based on the ideXlab platform.
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synergy between two metal catalysts a highly active silica supported bimetallic w zr catalyst for metathesis of n decane
Journal of the American Chemical Society, 2016Co-Authors: Manoja K Samantaray, Santosh Kavitake, Edy Abouhamad, Anissa Bendjeriousedjerari, Ali Hamieh, Jean-marie BassetAbstract:A well-defined, silica-supported bimetallic precatalyst [≡Si–O–W(Me)5≡Si–O–Zr(Np)3] (4) has been synthesized for the first time by successively grafting two organometallic complexes [W(Me)6 (1) followed by ZrNp4 (2)] on a single silica support. Surprisingly, multiple-quantum NMR characterization demonstrates that W and Zr species are in close proximity to each other. Hydrogenation of this bimetallic catalyst at room temperature showed the easy formation of Zirconium Hydride, probably facilitated by tungsten Hydride which was formed at this temperature. This bimetallic W/Zr Hydride precatalyst proved to be more efficient (TON = 1436) than the monometallic W Hydride (TON = 650) in the metathesis of n-decane at 150 °C. This synergy between Zr and W suggests that the slow step of alkane metathesis is the C–H bond activation that occurs on Zr. The produced olefin resulting from a β-H elimination undergoes easy metathesis on W.
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Synergy between Two Metal Catalysts: A Highly Active Silica-Supported Bimetallic W/Zr Catalyst for Metathesis of n‑Decane
2016Co-Authors: Manoja K Samantaray, Santosh Kavitake, Ali Hamieh, Raju Dey, Edy Abou-hamad, Anissa Bendjeriou-sedjerari, Jean-marie BassetAbstract:A well-defined, silica-supported bimetallic precatalyst [Si–O–W(Me)5Si–O–Zr(Np)3] (4) has been synthesized for the first time by successively grafting two organometallic complexes [W(Me)6 (1) followed by ZrNp4 (2)] on a single silica support. Surprisingly, multiple-quantum NMR characterization demonstrates that W and Zr species are in close proximity to each other. Hydrogenation of this bimetallic catalyst at room temperature showed the easy formation of Zirconium Hydride, probably facilitated by tungsten Hydride which was formed at this temperature. This bimetallic W/Zr Hydride precatalyst proved to be more efficient (TON = 1436) than the monometallic W Hydride (TON = 650) in the metathesis of n-decane at 150 °C. This synergy between Zr and W suggests that the slow step of alkane metathesis is the C–H bond activation that occurs on Zr. The produced olefin resulting from a β-H elimination undergoes easy metathesis on W
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from synthesis to chemical reactivity of supported d0 complexes part 1 an in situ infrared spectroscopic study of silica anchored Zirconium Hydrides
Journal of The Chemical Society-dalton Transactions, 1994Co-Authors: Francoise Quignard, Christine Lecuyer, Agnes Choplin, Jean-marie BassetAbstract:Silica-anchored Zirconium Hydride complexes have been synthesized by controlled hydrogenolysis of a tris(neopentyl)Zirconium surface complex. They have been characterized spectroscopically and their chemical reactivity compared to related molecular analogues. The mechanism of their formation is discussed. High reactivity and thermal stability seem to be correlated to the presence around Zr of the ‘solid’ ligand; its influence is discussed in terms of electronic and immobilizing effects.
