... J. Phys. D: Appl. Phys., 24 (1991), p. 2202. [14] P. Srirama Murti and MV Krishnaiah. Mater. ... more ... J. Phys. D: Appl. Phys., 24 (1991), p. 2202. [14] P. Srirama Murti and MV Krishnaiah. Mater. Lett., 11 (1991), p. 63. [15] G. Suresh, G. Seenivasan, MV Krishnaiah and P. Srirama Murti. J. Alloys Compd., 269 (1998), p. L9. [16] RD Cowan. J. Appl. Phys., 34 (1963), p. 926. ...
Cermets offer the benefits of both ceramics and metals. Due to the benefits associated with cerme... more Cermets offer the benefits of both ceramics and metals. Due to the benefits associated with cermets, especially high temperature stability and thermal conductivity, there is renewed interest in their thermophysical properties. The present work describes thermal conductivity studies on selected cermets using laser flash technique in the temperature range 673-1373 K. This work describes the preparation and thermal conductivity measurement of urania-nickel cermets of composition 20 and 30 wt.% nickel by the solid-state reaction method. The thermal conductivity value is obtained as a product of the measured thermal diffusivity, estimated specific heat and room temperature density of these cermets. The theoretical value of the thermal conductivity is also computed for these cermets using different models for two-phase solid mixtures, such as parallel, series and Maxwell models. The calculated thermal conductivity, obtained using measured thermal diffusivity, of these cermets is compared with the theoretical values from the above models. Thermal conductivity integral values are also calculated and presented here.
Thermal diffusivity and thermal conductivity studies were carried out on zirconate, uranate and c... more Thermal diffusivity and thermal conductivity studies were carried out on zirconate, uranate and cerate of strontium employing the laser flash technique. Based on the variation of the thermal resistivity as a function of temperature the heat transport behaviour of these oxide materials has been explained.
The solubility of 3PB material was determined by five different solvents. THF has high solubility... more The solubility of 3PB material was determined by five different solvents. THF has high solubility compare to other solvents. Unidirectional 〈100〉 plane of 3PB single crystal was grown by Sankaranarayanan-Ramasamy method. Fluorescence lifetime was analyzed, prompt and delayed lifetime was obtained at 12 ns and 30 ns respectively. The grown crystal was analyzed TG/ DTA and it was stable up to 164 C.
ABSTRACT Sodium is used as coolant in fast reactors. Sodium adhering to the reactor components is... more ABSTRACT Sodium is used as coolant in fast reactors. Sodium adhering to the reactor components is required to be removed before commencement of maintenance activities. In water vapour–carbon dioxide process, sodium is removed from the components by reacting it with water vapour carried by gaseous carbon dioxide. Hydrogen is formed during the above process. Since hydrogen forms an explosive mixture with air beyond explosion limit of 4%, monitoring hydrogen in carbon dioxide is required before being let out to the atmosphere. Quantification of hydrogen also gives an estimate on the progress of the cleaning process. A fuel cell based amperometric hydrogen sensor, H2/Pt//Nafion//Pt/O2, has been developed and applied for the purpose. The paper discusses the details of the sensor, its response behavior for hydrogen in carbon dioxide and its application for hydrogen monitoring in a simulated lab scale sodium cleaning experiment. The paper also illustrates the application of the sensor to hydrogen monitoring in mock up studies on sodium cleaning of a major component of Prototype Fast Breeder reactor (PFBR) namely Failed Fuel Location Module (FFLM).
ABSTRACT Monazite is one of the candidate ceramic matrices for the immobilization of high level r... more ABSTRACT Monazite is one of the candidate ceramic matrices for the immobilization of high level radioactive waste (HLW) from the reprocessing of spent nuclear fuel. The monazite phase, Ce0.8Ca0.2PO4, can accommodate cations of different valences due to the mixed valence state (+3 and +4) of Ce in this compound, by facilitating the oxidation and reduction of the Ce3+ and Ce4+ as required by the in-coming cation. This will assist in accommodating HLW of different compositions in the monazite crystal structure even if the average valence of the HLW elements is other than 3. Therefore, the monazite phase, Ce0.8Ca0.2PO4, can be a versatile host for the immobilization of HLW. The enthalpy increment and heat capacity of this versatile monazite phase and a simulated waste form based on it with 20 mass% HLW oxides were measured by drop calorimetry in the temperature range from 373 to 873 K, and the results are compared with those measured for CePO4.
Powder X-ray diffraction data are reported for RE6UO12 (RE=Eu, Gd, and Dy). The powders were prep... more Powder X-ray diffraction data are reported for RE6UO12 (RE=Eu, Gd, and Dy). The powders were prepared by a solution combustion method using urea as fuel. All compositions exhibit a rhombohedral structure with hexagonal unit cell parameters of a=1.012 67 (9) nm, c=0.9601 (1) nm for Eu6UO12; a=1.008 78 (6) nm, c=0.954 24 (7) nm for Gd6UO12; and a=0.998 06 (7) nm, c=0.944 03 (8) nm for Dy6UO12. The diffraction patterns of all the compounds are indexed on the R3¯ space group with Z=3. The a and c values decrease with increasing atomic number of the rare earth ion.
Improved method of data acquisition and processing for the measurement of thermal diffusivity by ... more Improved method of data acquisition and processing for the measurement of thermal diffusivity by the laser flash technique. [Review of Scientific Instruments 73, 3353 (2002)]. MV Krishnaiah, G. Seenivasan, P. Srirama Murti. Abstract. ...
A model based on simple thermodynamic consideration for calculating oxygen potentials of mixed ur... more A model based on simple thermodynamic consideration for calculating oxygen potentials of mixed uranium-plutonium oxide fuel was developed. Oxygen potential values obtained using this model are presented as a function of temperature and O/M ratio for mixed oxide fuel containing 15 to 30 mol% plutonium oxides. Comparison with experimental data from the literature shows reasonably good agreement.
An improved polymer electrolyte membrane fuel cell-based amperometric hydrogen sensor has been de... more An improved polymer electrolyte membrane fuel cell-based amperometric hydrogen sensor has been developed. The sensor operates at room temperature, and the electrolyte used in the sensor is Nafion which is a protonconducting solid polymer electrolyte. Platinum black is used as both anode and cathode. The sensor functions as a fuel cell, H 2 /Pt//Nafion//Pt/O 2 , and a mechanical barrier limits the supply of hydrogen to the sensing side electrode. The limiting current is found to be linearly related to the hydrogen concentration. The sensor can be used to measure hydrogen in argon in parts per million and percentage levels. The basic principle, details of assembly, and response behavior of the sensor are discussed.
(U, Pu) mixed oxides, (U 1Ày Pu y)O 2Àx , with y = 0.21 and 0.28 are being considered as fuels fo... more (U, Pu) mixed oxides, (U 1Ày Pu y)O 2Àx , with y = 0.21 and 0.28 are being considered as fuels for the Prototype Fast Breeder Reactor (PFBR) in India. The use of urania-plutonia solid solutions in PFBR calls for accurate measurement of physicochemical properties of these materials. Hence, in the present study, oxygen potentials of (U 1Ày Pu y)O 2Àx , with y = 0.21 and 0.28 were measured over the temperature range 1073-1473 K covering an oxygen potential range of À550 to À300 kJ mol À1 (O/M ratio from 1.96 to 2.000) by employing a H 2 /H 2 O gas equilibration technique followed by solid electrolyte EMFmeasurement. (U 1Ày Pu y)O 2Àx , with y = 0.40 is being used in the Fast Breeder Test Reactor (FBTR) in India to test the behaviour of fuels with high plutonium content. However, data on the oxygen potential as well as thermal conductivity of the mixed oxides with high plutonium content are scanty. Hence, the thermal diffusivity of (U 1Ày Pu y)O 2 , with y = 0.21, 0.28 and 0.40 was measured and the results of the measurements are reported.
Calculations were performed on hypo-stoichiometric uranium plutonium di-oxide to examine its vapo... more Calculations were performed on hypo-stoichiometric uranium plutonium di-oxide to examine its vaporization behavior as a function of O/M(M=U+Pu) ratio and plutonium content. The phase U(1−y)PuyOz was treated as an ideal solid solution of (1−y)UO2+yPuO(2−x) such that x=(2−z)/y. Oxygen potentials for different desired values of y, z, and temperature were used as the primary input to calculate the corresponding partial pressures of various O-, U-, and Pu-bearing gaseous species. Relevant thermodynamic data for the solid phases UO2 and PuO(2−x), and the gaseous species were taken from the literature. Total vapor pressure varies with O/M and goes through a minimum. This minimum does not indicate a congruently vaporizing composition. Vaporization behavior of this system can at best be quasi-congruent. Two quasi-congruently vaporizing compositions (QCVCs) exist, representing the equalities (O/M)vapor=(O/M)mixed−oxide and (U/Pu)vapor=(U/Pu)mixed−oxide, respectively. The (O/M) corresponding to QCVC1 is lower than that corresponding to QCVC2, but very close to the value where vapor pressure minimum occurs. The O/M values of both QCVCs increase with decrease in plutonium content. The vaporization chemistry of this system, on continuous vaporization under dynamic condition, is discussed.
Sodium zirconium phosphate, NZP, ideally NaZr2 (PO4) 3, is a potential host matrix for nuclear wa... more Sodium zirconium phosphate, NZP, ideally NaZr2 (PO4) 3, is a potential host matrix for nuclear waste. Thermophysical properties of these materials are necessary to assess the thermal stability of these compounds. This paper presents the synthesis and calorimetric ...
... J. Phys. D: Appl. Phys., 24 (1991), p. 2202. [14] P. Srirama Murti and MV Krishnaiah. Mater. ... more ... J. Phys. D: Appl. Phys., 24 (1991), p. 2202. [14] P. Srirama Murti and MV Krishnaiah. Mater. Lett., 11 (1991), p. 63. [15] G. Suresh, G. Seenivasan, MV Krishnaiah and P. Srirama Murti. J. Alloys Compd., 269 (1998), p. L9. [16] RD Cowan. J. Appl. Phys., 34 (1963), p. 926. ...
Cermets offer the benefits of both ceramics and metals. Due to the benefits associated with cerme... more Cermets offer the benefits of both ceramics and metals. Due to the benefits associated with cermets, especially high temperature stability and thermal conductivity, there is renewed interest in their thermophysical properties. The present work describes thermal conductivity studies on selected cermets using laser flash technique in the temperature range 673-1373 K. This work describes the preparation and thermal conductivity measurement of urania-nickel cermets of composition 20 and 30 wt.% nickel by the solid-state reaction method. The thermal conductivity value is obtained as a product of the measured thermal diffusivity, estimated specific heat and room temperature density of these cermets. The theoretical value of the thermal conductivity is also computed for these cermets using different models for two-phase solid mixtures, such as parallel, series and Maxwell models. The calculated thermal conductivity, obtained using measured thermal diffusivity, of these cermets is compared with the theoretical values from the above models. Thermal conductivity integral values are also calculated and presented here.
Thermal diffusivity and thermal conductivity studies were carried out on zirconate, uranate and c... more Thermal diffusivity and thermal conductivity studies were carried out on zirconate, uranate and cerate of strontium employing the laser flash technique. Based on the variation of the thermal resistivity as a function of temperature the heat transport behaviour of these oxide materials has been explained.
The solubility of 3PB material was determined by five different solvents. THF has high solubility... more The solubility of 3PB material was determined by five different solvents. THF has high solubility compare to other solvents. Unidirectional 〈100〉 plane of 3PB single crystal was grown by Sankaranarayanan-Ramasamy method. Fluorescence lifetime was analyzed, prompt and delayed lifetime was obtained at 12 ns and 30 ns respectively. The grown crystal was analyzed TG/ DTA and it was stable up to 164 C.
ABSTRACT Sodium is used as coolant in fast reactors. Sodium adhering to the reactor components is... more ABSTRACT Sodium is used as coolant in fast reactors. Sodium adhering to the reactor components is required to be removed before commencement of maintenance activities. In water vapour–carbon dioxide process, sodium is removed from the components by reacting it with water vapour carried by gaseous carbon dioxide. Hydrogen is formed during the above process. Since hydrogen forms an explosive mixture with air beyond explosion limit of 4%, monitoring hydrogen in carbon dioxide is required before being let out to the atmosphere. Quantification of hydrogen also gives an estimate on the progress of the cleaning process. A fuel cell based amperometric hydrogen sensor, H2/Pt//Nafion//Pt/O2, has been developed and applied for the purpose. The paper discusses the details of the sensor, its response behavior for hydrogen in carbon dioxide and its application for hydrogen monitoring in a simulated lab scale sodium cleaning experiment. The paper also illustrates the application of the sensor to hydrogen monitoring in mock up studies on sodium cleaning of a major component of Prototype Fast Breeder reactor (PFBR) namely Failed Fuel Location Module (FFLM).
ABSTRACT Monazite is one of the candidate ceramic matrices for the immobilization of high level r... more ABSTRACT Monazite is one of the candidate ceramic matrices for the immobilization of high level radioactive waste (HLW) from the reprocessing of spent nuclear fuel. The monazite phase, Ce0.8Ca0.2PO4, can accommodate cations of different valences due to the mixed valence state (+3 and +4) of Ce in this compound, by facilitating the oxidation and reduction of the Ce3+ and Ce4+ as required by the in-coming cation. This will assist in accommodating HLW of different compositions in the monazite crystal structure even if the average valence of the HLW elements is other than 3. Therefore, the monazite phase, Ce0.8Ca0.2PO4, can be a versatile host for the immobilization of HLW. The enthalpy increment and heat capacity of this versatile monazite phase and a simulated waste form based on it with 20 mass% HLW oxides were measured by drop calorimetry in the temperature range from 373 to 873 K, and the results are compared with those measured for CePO4.
Powder X-ray diffraction data are reported for RE6UO12 (RE=Eu, Gd, and Dy). The powders were prep... more Powder X-ray diffraction data are reported for RE6UO12 (RE=Eu, Gd, and Dy). The powders were prepared by a solution combustion method using urea as fuel. All compositions exhibit a rhombohedral structure with hexagonal unit cell parameters of a=1.012 67 (9) nm, c=0.9601 (1) nm for Eu6UO12; a=1.008 78 (6) nm, c=0.954 24 (7) nm for Gd6UO12; and a=0.998 06 (7) nm, c=0.944 03 (8) nm for Dy6UO12. The diffraction patterns of all the compounds are indexed on the R3¯ space group with Z=3. The a and c values decrease with increasing atomic number of the rare earth ion.
Improved method of data acquisition and processing for the measurement of thermal diffusivity by ... more Improved method of data acquisition and processing for the measurement of thermal diffusivity by the laser flash technique. [Review of Scientific Instruments 73, 3353 (2002)]. MV Krishnaiah, G. Seenivasan, P. Srirama Murti. Abstract. ...
A model based on simple thermodynamic consideration for calculating oxygen potentials of mixed ur... more A model based on simple thermodynamic consideration for calculating oxygen potentials of mixed uranium-plutonium oxide fuel was developed. Oxygen potential values obtained using this model are presented as a function of temperature and O/M ratio for mixed oxide fuel containing 15 to 30 mol% plutonium oxides. Comparison with experimental data from the literature shows reasonably good agreement.
An improved polymer electrolyte membrane fuel cell-based amperometric hydrogen sensor has been de... more An improved polymer electrolyte membrane fuel cell-based amperometric hydrogen sensor has been developed. The sensor operates at room temperature, and the electrolyte used in the sensor is Nafion which is a protonconducting solid polymer electrolyte. Platinum black is used as both anode and cathode. The sensor functions as a fuel cell, H 2 /Pt//Nafion//Pt/O 2 , and a mechanical barrier limits the supply of hydrogen to the sensing side electrode. The limiting current is found to be linearly related to the hydrogen concentration. The sensor can be used to measure hydrogen in argon in parts per million and percentage levels. The basic principle, details of assembly, and response behavior of the sensor are discussed.
(U, Pu) mixed oxides, (U 1Ày Pu y)O 2Àx , with y = 0.21 and 0.28 are being considered as fuels fo... more (U, Pu) mixed oxides, (U 1Ày Pu y)O 2Àx , with y = 0.21 and 0.28 are being considered as fuels for the Prototype Fast Breeder Reactor (PFBR) in India. The use of urania-plutonia solid solutions in PFBR calls for accurate measurement of physicochemical properties of these materials. Hence, in the present study, oxygen potentials of (U 1Ày Pu y)O 2Àx , with y = 0.21 and 0.28 were measured over the temperature range 1073-1473 K covering an oxygen potential range of À550 to À300 kJ mol À1 (O/M ratio from 1.96 to 2.000) by employing a H 2 /H 2 O gas equilibration technique followed by solid electrolyte EMFmeasurement. (U 1Ày Pu y)O 2Àx , with y = 0.40 is being used in the Fast Breeder Test Reactor (FBTR) in India to test the behaviour of fuels with high plutonium content. However, data on the oxygen potential as well as thermal conductivity of the mixed oxides with high plutonium content are scanty. Hence, the thermal diffusivity of (U 1Ày Pu y)O 2 , with y = 0.21, 0.28 and 0.40 was measured and the results of the measurements are reported.
Calculations were performed on hypo-stoichiometric uranium plutonium di-oxide to examine its vapo... more Calculations were performed on hypo-stoichiometric uranium plutonium di-oxide to examine its vaporization behavior as a function of O/M(M=U+Pu) ratio and plutonium content. The phase U(1−y)PuyOz was treated as an ideal solid solution of (1−y)UO2+yPuO(2−x) such that x=(2−z)/y. Oxygen potentials for different desired values of y, z, and temperature were used as the primary input to calculate the corresponding partial pressures of various O-, U-, and Pu-bearing gaseous species. Relevant thermodynamic data for the solid phases UO2 and PuO(2−x), and the gaseous species were taken from the literature. Total vapor pressure varies with O/M and goes through a minimum. This minimum does not indicate a congruently vaporizing composition. Vaporization behavior of this system can at best be quasi-congruent. Two quasi-congruently vaporizing compositions (QCVCs) exist, representing the equalities (O/M)vapor=(O/M)mixed−oxide and (U/Pu)vapor=(U/Pu)mixed−oxide, respectively. The (O/M) corresponding to QCVC1 is lower than that corresponding to QCVC2, but very close to the value where vapor pressure minimum occurs. The O/M values of both QCVCs increase with decrease in plutonium content. The vaporization chemistry of this system, on continuous vaporization under dynamic condition, is discussed.
Sodium zirconium phosphate, NZP, ideally NaZr2 (PO4) 3, is a potential host matrix for nuclear wa... more Sodium zirconium phosphate, NZP, ideally NaZr2 (PO4) 3, is a potential host matrix for nuclear waste. Thermophysical properties of these materials are necessary to assess the thermal stability of these compounds. This paper presents the synthesis and calorimetric ...
Uploads
Papers by Mv Krishnaiah