The burnable poison Gadolinium oxide was incorporated into UO<sub>2</sub> in two of the 36 elements of the fuel assembly in the reload fuel of BWR Units I & II of Tarapur Atomic Power Station. This ena...The burnable poison Gadolinium oxide was incorporated into UO<sub>2</sub> in two of the 36 elements of the fuel assembly in the reload fuel of BWR Units I & II of Tarapur Atomic Power Station. This enabled loading of higher quantities of fuel and achieving a more flattened neutron flux distribution over a longer period of time in the nuclear reactor core. The UO<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> pellets are made by powder pressing and sintering. In the early days of this author’s experience of the 1970s, the processing of UO<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> turned out to be more complex than that of UO<sub>2</sub> alone. The small proportion of Gd<sub>2</sub>O<sub>3</sub> in the powder mixture (1.5%) is to be uniformly distributed in the UO<sub>2</sub> before and after sintering and substitutional solid solution formation must be complete prior to densification. The inadequacy of homogeneity in the powder and pressed pellets leads to severe defects in the sintering process. In this paper, the processing of U<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> has been revisited. The defects in the product such as “free gadolinia”, low sintered density and bloating, caused by improper processing, have been brought out. The structural defect chemistry aspects of UO<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> and diffusion processes relevant to sintering have also been discussed.展开更多
The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The...The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The mechanical properties of the MAF treated alloy were measured through universal tensile testing and Vickers hardness testing equipment.The zircaloy-4 deformed up to a cumulative strain of 5.91 showed improvement in both ultimate tensile strength and hardness from 474 MPa to 717 MPa and from HV 190 to HV 238,respectively,as compared with the as-received alloy.However,there was a noticeable decrement in ductility（from 18%to 3.5%） due to the low strain hardening ability of deformed zircaloy-4.The improvement in strength and hardness of the deformed alloy is attributed to the grain size effect and higher dislocation density generated during multiaxial forging.The microstructural evolutions of deformed samples were characterized by optical microscopy and transmission electron microscopy（TEM）.The evolved microstructure at a cumulative strain of 5.91 obtained after MAF up to 12 cycles depicted the formation of ultrafine grains with an average size of 150-250 nm.展开更多
Dominant phase during hot deformation in the two-phase region of Zr-2.5Nb-0.5Cu （ZNC） alloy was studied using activation energy calculation of individual phases. Thermo-mechanical compression tests were performed on...Dominant phase during hot deformation in the two-phase region of Zr-2.5Nb-0.5Cu （ZNC） alloy was studied using activation energy calculation of individual phases. Thermo-mechanical compression tests were performed on a two-phase ZNC alloy in the temperature range of 700-925 ℃ and strain rate range of 10-2-10 s-l, Flow stress data of the single phase were extrapolated in the two-phase range to calculate flow stress data of individual phases. Activation energies of individual phases were then calculated using calculated flow stress data in the two-phase range, Comparison of activation energies revealed that a phase is the dominant phase （deformation controlling phase） in the two-phase range. Constitutive equations were also developed on the basis of the deformation temperature range （or according to phases present） using a sine-hyperbolic type constitutive equation. The statistical analysis revealed that the constitutive equation developed for a particular phase showed good agreement with the experimental results in terms of correlation coefficient （R） and average absolute relative error （AARE）.展开更多
Thorium based nuclear fuel is of immense interest to India by virtue of the abundance of Thorium and relative shortage of Uranium. Thorium metal tubes were being cold drawn using copper as cladding to prevent die seiz...Thorium based nuclear fuel is of immense interest to India by virtue of the abundance of Thorium and relative shortage of Uranium. Thorium metal tubes were being cold drawn using copper as cladding to prevent die seizure. After cold drawing, the copper was removed by dissolution in nitric acid. Thorium does not dissolve being passivated by nitric acid. Initially the copper cladding was carried out by inserting copper tubes inside and outside the thorium metal tube. In an innovative development, the mechanical cladding with copper was replaced by electroplated copper with a remarkable improvement in thorium tube acceptance rates. Oxalate derived thoria powder was found to require lower compaction pressures compared to ammonium diuranate derived urania powders to attain the same green compact density. However, the green pellets of thoria were fragile and chipped during handling. The strength improved after introducing a ball milling step before compaction and maintaining the green density above the specified value. Alternatively, binders were used later for greater handling strength. Magnesia was conventionally being used as dopant to enhance the sinterability of thoria. The normal sintering temperature for magnesia doped thoria was 1600℃ - 1700℃, which was achieved in electrically heated molybdenum element sintering furnaces with reducing atmosphere. 0.25 mole percent addition of niobia to the thoria was found to bring down the sintering temperature to 1150℃. Sintering could be done in ordinary furnaces in air atmosphere using silicon carbide or Kanthal heating elements. Electrical conductivity was measured for both magnesia and niobia doped sintered thoria and used in interpreting differences in sintering behavior.展开更多
The texture and mechanical properties of cross-rolled zircaloy-2 at 77 and 300 K were investigated.Crossrolling at 77 K was performed to impart different thickness reductions of 25% and 50%,while at 300 K with 25%,50%...The texture and mechanical properties of cross-rolled zircaloy-2 at 77 and 300 K were investigated.Crossrolling at 77 K was performed to impart different thickness reductions of 25% and 50%,while at 300 K with 25%,50%,75% and 85% reductions to the sample.EBSD analysis of deformed sample showed that near-basal orientation is not deformed completely after 50% rolling reduction.The activation of prismatic silp,{1122} contraction twin and {1012} extension twin were evident from the deformed microstructure at 77 K.The propensity for activation of basal slip〈a〉 at77 K was also observed.The deformation of the sample at 300 K occurs by prismatic,basal 〈a〉 and pyramidal 〈c＋a〉slips,which were predicted by pole figures.After annealing,the tensile strengths（735 and 710 MPa） are almost the same for 50% cryo-cross-rolled and room-temperature cross-rolled zircaloy-2 with almost 2.7% difference in their ductility.KAM analysis of the deformed samples was made to estimate the stored strain energy and dislocation density.Annealing of deformed sample at 673 K for 30 min results in recrystallization,which leads to the formation of ultrafine grains.展开更多
India is one of the few countries committed to expansion of nuclear power. In view of the abundance of thorium relative to uranium, thorium cycle is under serious development and implementation. Both ThO2 and (U,Th)O2...India is one of the few countries committed to expansion of nuclear power. In view of the abundance of thorium relative to uranium, thorium cycle is under serious development and implementation. Both ThO2 and (U,Th)O2 are used. Fine powders of the same are mostly prepared through the aqueous chemical route, pressed and sintered. Extrusion and hot impact densification are also being used. Sol-gel method and other alternatives are also being pursued with the advantage of automation and remote operation. Relevant papers on the thorium cycle with emphasis on processing methods and related aspects are reviewed here.展开更多
文摘The burnable poison Gadolinium oxide was incorporated into UO<sub>2</sub> in two of the 36 elements of the fuel assembly in the reload fuel of BWR Units I & II of Tarapur Atomic Power Station. This enabled loading of higher quantities of fuel and achieving a more flattened neutron flux distribution over a longer period of time in the nuclear reactor core. The UO<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> pellets are made by powder pressing and sintering. In the early days of this author’s experience of the 1970s, the processing of UO<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> turned out to be more complex than that of UO<sub>2</sub> alone. The small proportion of Gd<sub>2</sub>O<sub>3</sub> in the powder mixture (1.5%) is to be uniformly distributed in the UO<sub>2</sub> before and after sintering and substitutional solid solution formation must be complete prior to densification. The inadequacy of homogeneity in the powder and pressed pellets leads to severe defects in the sintering process. In this paper, the processing of U<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> has been revisited. The defects in the product such as “free gadolinia”, low sintered density and bloating, caused by improper processing, have been brought out. The structural defect chemistry aspects of UO<sub>2</sub>-Gd<sub>2</sub>O<sub>3</sub> and diffusion processes relevant to sintering have also been discussed.
基金BRNS,Bombay for their financial grant to this work through grant No.BRN-577-MMD
文摘The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The mechanical properties of the MAF treated alloy were measured through universal tensile testing and Vickers hardness testing equipment.The zircaloy-4 deformed up to a cumulative strain of 5.91 showed improvement in both ultimate tensile strength and hardness from 474 MPa to 717 MPa and from HV 190 to HV 238,respectively,as compared with the as-received alloy.However,there was a noticeable decrement in ductility（from 18%to 3.5%） due to the low strain hardening ability of deformed zircaloy-4.The improvement in strength and hardness of the deformed alloy is attributed to the grain size effect and higher dislocation density generated during multiaxial forging.The microstructural evolutions of deformed samples were characterized by optical microscopy and transmission electron microscopy（TEM）.The evolved microstructure at a cumulative strain of 5.91 obtained after MAF up to 12 cycles depicted the formation of ultrafine grains with an average size of 150-250 nm.
基金financial support(Grant No.2011/36/15)from Board of Research in Nuclear Science(BRNS),India
文摘Dominant phase during hot deformation in the two-phase region of Zr-2.5Nb-0.5Cu （ZNC） alloy was studied using activation energy calculation of individual phases. Thermo-mechanical compression tests were performed on a two-phase ZNC alloy in the temperature range of 700-925 ℃ and strain rate range of 10-2-10 s-l, Flow stress data of the single phase were extrapolated in the two-phase range to calculate flow stress data of individual phases. Activation energies of individual phases were then calculated using calculated flow stress data in the two-phase range, Comparison of activation energies revealed that a phase is the dominant phase （deformation controlling phase） in the two-phase range. Constitutive equations were also developed on the basis of the deformation temperature range （or according to phases present） using a sine-hyperbolic type constitutive equation. The statistical analysis revealed that the constitutive equation developed for a particular phase showed good agreement with the experimental results in terms of correlation coefficient （R） and average absolute relative error （AARE）.
文摘Thorium based nuclear fuel is of immense interest to India by virtue of the abundance of Thorium and relative shortage of Uranium. Thorium metal tubes were being cold drawn using copper as cladding to prevent die seizure. After cold drawing, the copper was removed by dissolution in nitric acid. Thorium does not dissolve being passivated by nitric acid. Initially the copper cladding was carried out by inserting copper tubes inside and outside the thorium metal tube. In an innovative development, the mechanical cladding with copper was replaced by electroplated copper with a remarkable improvement in thorium tube acceptance rates. Oxalate derived thoria powder was found to require lower compaction pressures compared to ammonium diuranate derived urania powders to attain the same green compact density. However, the green pellets of thoria were fragile and chipped during handling. The strength improved after introducing a ball milling step before compaction and maintaining the green density above the specified value. Alternatively, binders were used later for greater handling strength. Magnesia was conventionally being used as dopant to enhance the sinterability of thoria. The normal sintering temperature for magnesia doped thoria was 1600℃ - 1700℃, which was achieved in electrically heated molybdenum element sintering furnaces with reducing atmosphere. 0.25 mole percent addition of niobia to the thoria was found to bring down the sintering temperature to 1150℃. Sintering could be done in ordinary furnaces in air atmosphere using silicon carbide or Kanthal heating elements. Electrical conductivity was measured for both magnesia and niobia doped sintered thoria and used in interpreting differences in sintering behavior.
基金BRNS,Bombay for their financial grant to this work (No.BRN-577-MMD)
文摘The texture and mechanical properties of cross-rolled zircaloy-2 at 77 and 300 K were investigated.Crossrolling at 77 K was performed to impart different thickness reductions of 25% and 50%,while at 300 K with 25%,50%,75% and 85% reductions to the sample.EBSD analysis of deformed sample showed that near-basal orientation is not deformed completely after 50% rolling reduction.The activation of prismatic silp,{1122} contraction twin and {1012} extension twin were evident from the deformed microstructure at 77 K.The propensity for activation of basal slip〈a〉 at77 K was also observed.The deformation of the sample at 300 K occurs by prismatic,basal 〈a〉 and pyramidal 〈c＋a〉slips,which were predicted by pole figures.After annealing,the tensile strengths（735 and 710 MPa） are almost the same for 50% cryo-cross-rolled and room-temperature cross-rolled zircaloy-2 with almost 2.7% difference in their ductility.KAM analysis of the deformed samples was made to estimate the stored strain energy and dislocation density.Annealing of deformed sample at 673 K for 30 min results in recrystallization,which leads to the formation of ultrafine grains.
文摘India is one of the few countries committed to expansion of nuclear power. In view of the abundance of thorium relative to uranium, thorium cycle is under serious development and implementation. Both ThO2 and (U,Th)O2 are used. Fine powders of the same are mostly prepared through the aqueous chemical route, pressed and sintered. Extrusion and hot impact densification are also being used. Sol-gel method and other alternatives are also being pursued with the advantage of automation and remote operation. Relevant papers on the thorium cycle with emphasis on processing methods and related aspects are reviewed here.
