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In a postulated severe accidental condition of sodium-cooled fast reactor (SFR), the eutectic reaction between boron carbide (B4C) as control rod element and stainless steel (SS) as control rod cladding or related structure materials may take place. Thus, the kinetic behavior of the B4C-SS eutectic reaction is one of the important phenomena to be considered when evaluating the core disruptive accidents in SFR. In this study, for the first step to obtain the fundamental information on kinetic feature of the B4C-SS eutectic reaction and compare the pervious findings, the thermal analysis using the pellet samples of B4C and Type 316L SS as a different experimental approach was performed up to 1773 K at different heating rates of 2.5-10 K min-1. The differential thermal analysis (DTA) endothermic peaks for the B4C-SS eutectic reaction appeared from 1483K to 1534K and systematically shifted to higher temperatures with increasing heating rate. Based on this kinetic feature, apparent activation energy and pre-exponential factor for the B4C-SS eutectic reaction were determined by Kissinger method. It was found that the kinetic parameters obtained by thermal analysis were comparable to the literature values of the thinning experiment at high temperatures. In addition, the microstructure and element distribution formed in the interdiffusion layer composed of the B4C-SS system were analyzed by the electron probe microanalyzer (EPMA), which can provide key validation data on elemental interdiffusion behavior in the early stage of the eutectic reaction for reflecting the reaction kinetic modeling.

One of the key issues in a core disruptive accident (CDA) evaluation in sodium-cooled fast reactors is eutectic reactions between boron carbide (B4C) and stainless steel (SS) as well as its relocation. Such behaviors have never been simulated in CDA numerical analyses in the past, therefore it is necessary to develop a physical model and incorporate the model into the CDA analysis code. This study focuses on B4C-SS eutectic melting experiments, thermophysical property measurement of the eutectic melt, and physical model development for the eutectic melting reaction. The eutectic experiments involve the visualization experiments, eutectic reaction rate experiments and material analyses. The thermophysical properties are measured in a range from solid to liquid state. The physical model is developed for a CDA computer code based on the measured data of the eutectic reaction rate and the physical properties. This paper describes the project overview and progress of experimental and analytical studies conducted until 2019. Specific results in this paper are the validation of physical model describing B4C-SS eutectic reaction in the CDA analysis code, SIMMER-III, through the numerical analysis of the B4C-SS eutectic melting experiments in which a B4C block was placed in a SS pool.

In a postulated severe accidental condition of sodium-cooled fast reactor (SFR), eutectic melting between boron carbide (B4C) as control rod element and stainless steel (SS) as control rod cladding or related structure may take place. Thus, kinetic behavior of B4C-SS eutectic melting is one of the important phenomena to be considered when evaluating the core disruptive accidents in SFR. In this study, for the first step to obtain the fundamental information on kinetic feature of B4C-SS eutectic melting and compare the pervious findings, the thermal analysis using the pellet type samples of B4C and Type 316L SS as different experimental technique was performed up to 1773 K at different heating rates of 2.5–10 K/min. The differential thermal analysis (DTA) endothermic peaks for the B4C-SS eutectic melting appeared from 1483K to 1534K and systematically shifted to higher temperatures when increasing heating rate. Based on this kinetic feature, apparent activation energy and pre-exponential factor for the B4C-SS eutectic melting were determined by Kissinger method. It was found that the kinetic parameters obtained by thermal analysis were comparable to the literature values of thinning experiment at high temperatures. In addition, the microstructure and element distribution formed in the interdiffusion layer composed of the B4C / SS system were analyzed by the electron probe microanalyzer (EPMA), which can provide key validation data on elemental interdiffusion behavior in the early stage of the eutectic melting.

One of the key issues in a core disruptive accident (CDA) evaluation in sodium-cooled fast reactors is eutectic reactions between boron carbide (B4C) and stainless steel (SS) as well as its relocation. Such behaviors have never been simulated in CDA numerical analyses in the past, therefore it is necessary to develop a physical model and incorporate the model into the CDA analysis code. This study focuses on B4C-SS eutectic melting experiments, thermophysical property measurement of the eutectic melt, and physical model development for the eutectic melting reaction. The eutectic experiments involve the visualization experiments, eutectic reaction rate experiments and material analyses. The thermophysical properties are measured in a range from solid to liquid state. The physical model is developed for a severe accident computer code based on the measured data of the eutectic reaction rate and the physical properties. This paper describes the project overview and progress of experimental and analytical studies conducted until 2018. Specific results in this paper are boron concentration distributions of solidified B4C-SS eutectic sample in the eutectic melting experiments, which would be used for the validation of the eutectic physical model implemented into the computer code.

The Central Research Institute of Electric Power Industry and Japan Atomic Energy Agency have fabricated the first sodium-bonded metallic fuel elements in Japan as a collaborative research for the irradiation test at the experimental fast test reactor Joyo. The U-20 wt.%Pu-10 wt.%Zr fuel slugs of 200 mm length and approximately 5 mm diameter were fabricated in a small-scale injection casting furnace using U metal, U-Pu alloy and Zr metal. The fuel slugs met the specifications determined on the basis of the specifications of the Experimental Breeder Reactor II driver fuels in the United States and the results of preliminary casting tests. Each fuel slug was loaded into a ferritic-martensitic stainless steel (PNC-FMS) cladding tube with a few pieces of sodium rods as thermal bonds, the U-10 wt.%Zr thermal insulator and the PNC-FMS reflector in a helium gas atmosphere glove box. After top-end plug welding to the cladding tube and the heat treatment of the welding area, each fuel element was subjected to sodium bonding to fill the annular gap between the fuel slug and the cladding with the melted sodium. After inspection, six metallic fuel elements were manufactured successfully and transferred to the Joyo site.

A high-purity Ar gas atmosphere glove box accommodating injection casting and sodium-bonding apparatuses was newly installed in the Plutonium Fuel Research Facility of Oarai Research and Development Center, Japan Atomic Energy Agency, in which several nitride and carbide fuel pins were fabricated for irradiation tests. The experiences led to the establishment of the technological basis of the fabrication of U-Pu-Zr alloy fuel pins for the first time in Japan. After the injection casting of the U-Pu-Zr alloy, the metallic fuel pins were fabricated by welding upper and lower end plugs with cladding tubes of ferritic-martensitic steel. Subsequent to the sodium bonding for filling the annular gap region between the U-Pu-Zr alloy and the cladding tube with the melted sodium, the fuel pins for irradiation tests are inspected. This paper shows the apparatuses and the technological basis for the fabrication of U-Pu-Zr alloy fuel pins for the irradiation test planned at the experimental fast test reactor Joyo.

To assist in understanding metal fuel performance at elevated temperatures, phase diagrams of the U–Pu–Zr, U–Pu–Fe, U–Zr–Fe and U–Pu–Zr–Fe systems at 800 °C were calculated based on thermodynamic data that has been previously evaluated. The calculated phase diagrams were compared with phase composition data at the interdiffusion zones, which formed at the interface between the irradiated or unirradiated U–Pu–Zr metal fuel and stainless steel cladding at temperatures of 800 °C or higher in literature. Each phase formed at the interface was successfully identified. It was confirmed that even in transient tests of the irradiated fuel pins, these phase diagrams are applicable to analysis of the multi-component interdiffusion zones between the metal fuel and the iron-based cladding.

The phase diagram in the quaternary Fe–Pu–U–Zr system was established at 923 K in the uranium-rich region to understand better the compatibility between the metal fuel and stainless steel cladding in a fast reactor. The experimental phase relation data obtained in this study was applied to the thermodynamic methodology for construction of the phase diagram. The calculated phase diagram was consistent and well within the experimental data. The applicability of the thermodynamic model to other temperatures was confirmed by comparing the present results of differential thermal analysis with the calculated phase diagrams. These consistencies mean that both the thermodynamic model and the assessed parameters in the binary and ternary subsystems developed so far are reasonable. The calculated phase diagram established in this study was also in good agreement with the analysis of the diffusion zone in tests on Pu–U–Zr/Fe couples. This suggests that the diffusion zone formed at the fuel–cladding interface in the reactor system can be assessed using the phase diagram in the quaternary Fe–Pu–U–Zr system.

An isothermal section of the Fe-Pu-U ternary system at 650 °C was assessed in a previous study. In the present study, the predictions of the phase relations in the Fe-Pu-U system to higher and lower temperatures were performed by applying the interaction parameters determined at 650 °C. Differential thermal analysis (DTA) for the Fe-Pu-U alloys was also carried out to confirm the phase relations in the temperature region of 500 to 800 °C. Both results agreed well. On the basis of the predicted ternary phase diagram, the phase relations for a region surrounded by Fe2Pu, Fe2U, U, and Pu were described by a reaction scheme and a projection of the liquidus surface.

The quaternary U–Pu–Zr–Fe system was assessed using thermodynamic and phase diagram data in order to evaluate fuel-cladding chemical interactions (FCCI) of metallic fuel in a fast reactor. The Gibbs energy of mixing for solution phases and the Gibbs energy of formation of compounds in the binary sub-systems were calculated using an optimization procedure. The use of such data in optimizing the binary sub-systems enabled appropriate calculations for the thermodynamic properties of the systems, which were also important when extrapolating to higher-order systems. Isotherms of ternary sub-systems were calculated by using the optimized parameters of the binary sub-systems. Based on the phase relation data measured in regions of the ternary systems, the isotherms were then modified by adding ternary interaction parameters. The calculation results agreed well with the experimental data points. Finally, the quaternary system was assessed. The phase relationship observed experimentally in the diffusion couple of U–Pu–Zr–Fe was in reasonable agreement with the calculated phase diagrams.

In metallic U-Pu-Zr fuel for fast reactors, metallurgical reactions occur between the fuel alloy and the stainless steel cladding, and a liquid phase may be formed in the reaction zone at a higher temperature. In order to clarify the condition for liquefaction at the fuel-cladding interface, the reactions of U-Pu alloys with Fe have been examined at 923 and 943 K. The test results confirmed that the liquid phase is not formed at 923 K in any region of the reaction zone when the maximum Pu content in the (U,Pu)6Fe phase is less than the Pu solubility limit in this phase. Comparison of the present test results with the liquefaction data from the various tests on metallic fuel-cladding compatibility suggested that the liquefaction condition is independent of the Zr content in the fuel alloy and can be expressed as a function of the atom fraction ratio of Pu/(U+Pu) in the fuel alloy and the reaction temperature. At 923 K, liquefaction will occur when the Pu/(U+Pu) ratio is larger than 0.25.

In metallic U-Pu-Zr fuel, metallurgical reactions occur between the fuel slug and the cladding, and a phase of which the melting point is relatively low is formed in the reaction zone. If a liquid phase is formed, it can degrade cladding integrity. The potential for liquid phase formation near the cladding, therefore, should be excluded during normal reactor operation. In order to clarify the mechanism of liquefaction, the authors have conducted diffusion experiments at 923 K using two couples: U-13 at%Pu-22 at%Zr/Fe and U-22at%Pu- 22at%Zr/Fe, and examined the influence of the Pu content in the fuel alloy on the phases formed in the reaction zones. The liquid phase has been observed in the U-22 at%Pu-22 at%Zr/Fe couple. An assessment of the diffusion paths for these couples has indicated that the Pu content in the (U, Pu)6Fe-type phase in the reaction zone is a crucial factor in determining the conditions that lead to liquefaction. The Pu content in the (U, Pu)6Fe-type phase increases with that in the ini...

The fate of 6alpha- and 6beta-hydrogens of lathosterol during the transformation into 20-hydroxyecdysone was chased by feeding [3alpha,6beta-2H2]- and [3alpha,6alpha-2H2]-lathosterols to hairy roots of Ajuga reptans var. atropurpurea. The behavior of 6beta-hydrogen, which mostly migrated to the C-5 position of 20-hydroxyecdysone, was in agreement with that of C-6 hydrogen of cholesterol. The results strongly supported the view that cholesterol and lathosterol are first metabolized into 7-dehydrocholesterol, which is then converted into 20-hydroxyecdysone via 7-dehydrocholesterol 5alpha,6alpha-epoxide in the hairy roots.

Equilibrium phase relations in the U–Zr–Fe ternary system have been investigated experimentally at 853, 973 and 1073 K. The composition of each phase has been determined using the electron probe microanalysis. The differential thermal analysis has also been applied to check the phase relations and examine the stabilities of the ternary compounds. The compositions of the phases found near the sub-binary edges are consistent with the published binary phase diagrams. Three ternary compounds have been found and designated e, λ and χ, the compositions of which are U–(33–50)Zr–33Fe, U–(21–25)Zr–6Fe and U–32Zr–50Fe (at.%), respectively. The single e-phase melts at 1206 ± 5 K. The λ-phase decomposes to e and γ at 999 ± 2 K. The χ-phase exists up to 1168 ± 10 K at the lowest. The equilibrium phase diagrams determined or estimated from the experimental results are consistent with the diagrams calculated using thermodynamic models.

The reaction zones formed in two kinds of diffusion couples: U–23at.%Zr/Fe and U–23at.%Zr/Fe–12at.%Cr, at 908, 923, 953, 973 and 988 K have been examined using the electron-probe microanalysis. In the U–Zr/Fe–Cr couples, diffusion of Cr to the U–Zr side is slower than that of Fe, and the Cr-rich phase is formed adjacent to the unreacted Fe–Cr alloy. Except for the Cr-rich phase, the measured compositions of the phases in the reaction zones in both U–Zr/Fe and U–Zr/Fe–Cr couples have corresponded well to those in the U–Zr–Fe ternary system. Each reaction zone can be divided to several layers. For the U–Zr side of the reaction zone, the configurations of the schematic diffusion paths, which are the curves connecting the average compositions of these layers on the U–Zr–( Fe + Cr ) composition triangle, are independent of the annealing temperature and the Cr addition to Fe. For the Fe(–Cr) side, however, the paths depend on the annealing temperature and the Cr addition to Fe. Some of the phases that are expected to emerge considering the schematic diffusion path and the U–Zr–Fe phase diagram have not been found at 988 K.

The partial vapor pressures of La(g) and U(g) over La x U 1− x alloys ( x =0.01, 0.02, 0.05, 0.20, 0.99) and Ce(g) and U(g) over Ce x U 1− x alloys ( x =0.01, 0.02, 0.04, 0.10, 0.20, 0.97, 0.99) were measured with a time-of-flight mass-spectrometer equipped with a tungsten Knudsen cell over the temperature range between 1619 and 1886 K. The thermodynamic activities of lanthanum or cerium and uranium in the liquid alloys were calculated from the ion intensity ratios of two components (lanthanum or cerium and uranium) in the alloys using the equation derived by Belton and Fruehan. These systems were found to exist as the two phases in the wide compositional range and to exhibit positive deviations from ideal behavior. The Gibbs free energy of formation was calculated from the thermodynamic activity values.

In an attempt to understand the phase formation mechanism at the interface of metal fuel and cladding, the isothermal phase diagrams and chemical potential diagrams of the Fe–U–Zr ternary system were calculated using the optimized interaction parameters of three binary subsystems. The Gibbs energies of solution phases and compounds in the Fe–U and U–Zr systems were calculated through an optimization procedure based on both the experimental thermochemical and phase diagram data. The obtained ternary phase diagrams were consistent with the experimental data, when the Gibbs energies of formation of ternary compounds; Fe 0.06 U 0.71 Zr 0.23 and Fe 0.3 U 0.3 Zr 0.4 , were assumed to be −3.7∼−4.3 and −16∼−17.5 kJ per g-atom, respectively. The calculated chemical potential diagrams described satisfactorily the experimental diffusion path for the U 0.8 Zr O.2 /Fe couple at 923 K.

The partial vapor pressures of La(g) and Ce(g) over La x Ce 1− x alloys ( x =0.00, 0.05, 0.29, 0.50, 0.80, 1.00) were measured with a time-of-flight mass-spectrometer equipped with a tungsten Knudsen cell over the temperature range of 1592–1781 K. The thermodynamic activities of lanthanum and cerium in the liquid alloys were determined by comparing the partial vapor pressures of La(g) and Ce(g) over the alloys with those over the pure metals, respectively. The thermodynamic activities were also calculated from the ion intensity ratios of two components (lanthanum and cerium) in the alloys using the equation derived by Belton and Fruehan. Both activities for each element, thus obtained, were in good agreement with each other and almost obeyed Raoult's law. The partial molar Gibbs free energy, and the Gibbs free energy of formation were calculated from the thermodynamic activity values.

The vapor pressures of La(g) and Gd(g) over La x Gd 1− x alloys ( x = 0.00, 0.12, 0.22, 0.45, 0.70, 0.74, 0.85, 1.00) were measured with a time-of-flight mass spectrometer equipped with a tungsten Knudsen cell over the temperature range 1588 to 1797 K. The chemical activities of lanthanum and gadolinium in the alloys were determined by comparing the vapor pressures of La(g) and Gd(g) over the alloys with those over the pure metals. The chemical activities, thus obtained, showed positive deviations from Raoult's law over the entire compositional range. The interatomic force between gadolinium and lanthanum was thought to be repulsive. The partial molar Gibbs free energy and the Gibbs free energy, enthalpy and entropy of formation were calculated from the activity values.

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. The phase diagrams of the pseudo-binary systems of LiCl-KCl eutectic and lanthanide trichloride (LnCl 3 : Ln=La, Ce, Pr, Nd, Sm, and Gd) were determined for compositions less than 25 mol% LnCl 3 by means of thermal analysis, visual observation, electromotive force measurement and powder X-ray diffraction. The existence of K 2 LnCl 5 compounds was confirmed in all the systems, but K 3 LnCl 6 was observed only in the systems containing Sm and Gd. In the region up to 17 mol% LnCl 3 , the eutectic temperature and composition were observed to be close to those of the LiCl-KCl eutectic system (625±1 K, LiCl-41 at.% KCl). For compositions greater than 17 mol% LnCl 3 , on the other hand, the eutectic points were 701±1, 691±1, 681±1, 656±1, 635±1 and 649±1 K for La, Ce, Pr, Nd, Sm, and Gd, respectively. The liquidus surface of the LiCl-KCl-LaCl 3 system was also determined at compositions up to 40 mol% LnCl 3 . © 1997 Elsevier Science B.V.

Feeding of deuterium labeled cholesterols including [6- 2 H]cholesterol and [3α,6- 2 H 2 ]-cholesterol to hairy roots of Ajuga reptans var. atropurpurea followed by 2 H-NMR analysis of the biosynthesized 20-hydroxyecdysone revealed that most of the deuterium atom located at C-6 of cholesterol migrated to the C-5 position of 20-hydroxyecdysone.

Isotope effects were investigated for strontium and barium complexes of dicyclohexano-18-crown-6. The isotopes of odd mass number behaved differently than those of even mass number. A value of e0/E which represents the difference between the isotope of odd mass number and that of even mass number, was -0.0017 for 87Sr,-0.011 for 135Ba,and -0.009 for 137Ba. The unit mass enrichment factors were eu = -0.0009 for strontium and eu = 0.004 for barium. The direction of enrichment was opposite for strontium and barium, and the absolute value of the enrichment factor of barium was larger than that of strontium isotopes. This phenomenon was attributed to the difference in the predominant form of the strontium and barium ions in the aqueous solution. That is, the population of aquo-complexes is larger than that of anionic complexes for strontium, while the reverse is the case for barium.

Feeding of deuterium labeled cholesterols including [6- 2 H]cholesterol and [3α,6- 2 H 2 ]-cholesterol to hairy roots of Ajuga reptans var. atropurpurea followed by 2 H-NMR analysis of the biosynthesized 20-hydroxyecdysone revealed that most of the deuterium atom located at C-6 of cholesterol migrated to the C-5 position of 20-hydroxyecdysone.