Thermodynamic assessments of the Bi-U and Bi-Mn systems

The Bi-U and Bi-Mn binary systems have been critically assessed by using the CALPHAD (Calculation of Phase Diagrams) technique on the basis of the experimental data including thermodynamic properties and phase equilibria. The Gibbs free energies of the solution phases (liquid, bcc, fcc, αU, βU, αMn, (Bi), and βMn) were modeled by a sub-regular solution model with the Redlich-Kister equation, and those of the intermetallic compounds (UBi, U₃Bi₄, UBi₂, αBiMn and βBiMn) in these two binary systems were described by a two-sublattice model. A proper set of thermodynamic parameters has been derived for describing the Gibbs free energies of each phase in the Bi-U and Bi-Mn systems. An agreement between the calculated results and experimental data is obtained.     

First-principles study of structural, elastic and electronic properties of thorium dicarbide (ThC2) polymorphs

The comparative study of the structural, elastic, cohesive and electronic properties of three polymorphs (α-monoclinic, β-tetragonal and γ-cubic) of thorium dicarbide ThC₂ is performed within the density-functional theory. The optimized atomic coordinates, lattice parameters, theoretical density (ρ), bulk moduli (B), compressibility (β), as well as electronic densities of states, electronic heat capacity (γ) and molar Pauli paramagnetic susceptibility (χ) for all ThC₂ polymorphs are obtained and analyzed in comparison with available experimental data. The peculiarities of inter-atomic bonding for thorium dicarbide are discussed. Besides, we have evaluated the formation energies (E_f) of ThC₂ polymorphs for different possible preparation routes (namely for the reactions with the participation of simple substances (metallic Th and graphite) or thorium monocarbide ThC and graphite). The results show that the synthesis of the ThC₂ polymorphs from simple substances is more favorable - in comparison with the reactions with participation of Th monocarbide.     

Recent contribution of JET to the ITER physics

In recent years the JET scientific programme has focussed on addressing physics issues essential for the consolidation of design choices and the efficient exploitation of ITER in parallel to qualifying ITER operating scenarios and developing advanced control tools. This paper reports on recent achievements in the following areas: mitigation of edge localised modes (ELMs), effects of toroidal field (TF) ripple, advanced tokamak scenarios, material migration and fuel retention. Active methods have been developed to mitigate ELMs without adversely affecting confinement. A systematic characterisation of the edge plasma, pedestal energy and ELMs, and their impact on plasma-facing components as well as their compatibility with material limits has been performed. The unique JET capability of varying the TF ripple from its normal low value δB_T = 0.08% up to δB_T = 1% has been used to elucidate the role of TF ripple on confinement and ELMs. Increased TF ripple in ELMy H-mode plasmas is found to have a detrimental effect on plasma stored energy and density, especially at low collisionality. The development of ITER advanced tokamak scenarios has been pursued. In particular, β_N values above the ‘no-wall limit’ (β_N ～ 3.0) have been sustained for a resistive time. Gas balance studies combined with shot-resolved measurements from deposition monitors and divertor spectroscopy have confirmed the strong role of fuel co-deposition with carbon in the retention mechanism through long-range migration and also provided further evidence for the important role of ELMs in the material migration process within the JET inner divertor leg.     

Gas Chromatographic Characteristics of Polytrifluoromonochloroethylene Columns as applied to Analysis of Uranium Hexafluoride and other Volatile Inorganic Fluorides

A gas chromatographic assembly for analyzing UF₆ and other volatile inorganic fluorides was constructed. Column packings were consisted of polytrifluoromonochloroethylene oil as partition liquid, and moulding powder as supporting solid, both substances being inert to UF₆ if the operation temperature is not too high.

Through examination of the curves for peak height ratio between elution and inlet, it was found that, to obtain reproducible results, it was necessary to pretreat the columns by fluorine, use purified carrier gas, and establish a definite time schedule for sample introduction.

Dependence of HETP on (1) flow rate of carrier gas, (2) operation temperature, (3) degree of polymerization of polytriflizoromonochloroethylene oils, and (4) liquid phase loading were studied, and conditions for obtaining small HETP are discussed.

Gas chromatography of TeF₆ and MoF₆ were studied, and the possibility of separating these gases from UF₆ has been demonstrated.     

Thermal transport properties of hafnium hydrides and deuterides

The thermal conductivities of δ′-, δ-, δ+ε-, and ε-phase hafnium hydrides and deuterides with various hydrogen isotope concentrations (HfH_x, 1.48 ? x ? 2.03; HfD_x, 1.55 ? x ? 1.94) were evaluated within the temperature range of 290-570 K from the measured thermal diffusivity, calculated specific heat, and density. The thermal conductivities of δ′-, δ-, δ+ε-, and ε-phase HfH_x and HfD_x are independent of the temperature within the range 300-550 K and are in the range 0.15-0.22 W/cm K and 0.17-0.23 W/cm K, respectively; these values are similar to and lower than the observed thermal conductivities of α-phase Hf. The experimental results for the electrical resistivities of δ′-, δ-, δ+ε-, and ε-phase HfH_x and HfD_x and the Lorenz number corresponding to the electronic conduction, obtained from the Wiedemann-Franz rule, indicated that heat conduction due to electron migration significantly influences the thermal conductivity values at high temperatures. On the other hand, heat conduction due to phonon migration significantly affects the isotope effects on the thermal transport properties.     

A proposal of a benchmark for βeff, βeff/Λ, and Λ of thermal reactors fueled with slightly enriched uranium

A reactor noise approach has been successfully performed at the IPEN/MB-01 research reactor facility for the experimental determination of the delayed neutron parameters β_eff, β_eff/Λ, and Λ. In the measurement of the β_eff parameter, the reactor power, which is of fundamental importance, was obtained with a very high level of accuracy by a fuel rod scanning technique and a subsequent irradiation of a highly enriched ²³⁵U foil for the fission density normalization. The final measured values of β_eff and β_eff/Λ show very good agreement with independent measurements and can be recommended as benchmark values for thermal reactor applications because their uncertainties are much lower than the target accuracy recommended for β_eff calculations (|C-E|/E less than 3%). The theory/experiment comparisons reveal that only JENDL3.3 attends the target accuracy for β_eff calculations. This result fully supports the reduction of the ²³⁵U thermal yield as proposed by Okajima and Sakurai. The ENDF/B-VI.8 library and its revised version performed at LANL overpredict β_eff by as much as 7.2%. The newly released JEFF-3.1 library shows a discrepancy of 4.8% for β_eff. For β_eff/Λ, the deviations are relatively larger (more than 10%) for all libraries due to the underprediction of the prompt neutron generation time (Λ).     

Maximum scintillation yields in NaI(Tl) and CsI(Tl) crystals estimated from the scintillation model for liquid rare gases

The maximum scintillation yields in NaI(Tl) and CsI(Tl) crystals were estimated theoretically by applying the scintillation model for liquid rare gases to crystal scintillators. Average energies required to produce one scintillation photon in the maximum scintillation yield, W_so, were estimated to be 10.6 ± 0.3 or 11.6 ± 0.3 eV for NaI(Tl) and 11.6 ± 0.3 or 12.5 ± 0.3 eV for CsI(Tl). The new experiment on scintillation yields gives W_so of 10.8 ± 2.0 eV for NaI(Tl) and 11.3 ± 2.1 or 9.3 ± 1.7 eV for CsI(Tl). The values show good agreement with the theoretical estimations. These results demonstrate that the scintillation model in liquid rare gases is applicable to inorganic scintillators such as NaI(Tl) and CsI(Tl) crystals.     

Role of grain/phase boundary nature on the formation of hydrides in Zr-2.5%Nb alloy

Hydride formation in a fully recrystallized Zr-2.5%Nb alloy having equiaxed grains of α and β was studied. Primarily the electron back scatter diffraction (EBSD) technique was used for the characterization of the hydrides in conjunction with optical and transmission electron microscopy. Hydrides were found to have preferentially formed along the α/β interfaces. Microtexture measurements showed that the orientation relationship (OR) between α and δ-hydride phase was (0 0 0 1)_α || (1 1 1)_δ and || [1 1 0]_δ. It was shown that the hydrides have higher preference to form along such α/β interfaces which have one of the low index planes of the β phase constituting the interface.     

Calculation,measurement and sensitivity analysis of kinetic parameters of Tehran Research Reactor

Effective delayed neutron fraction β_eff and neutron generation time Λ are important factors in reactor physics calculation and transient analysis. In the first stage of this research, these kinetic parameters have been calculated for two states of Tehran Research Reactor (TRR), i.e. cold (fuel, clad and coolant temperatures equal to 20 °C) and hot (fuel, clad and coolant temperatures of 65, 49 and 44 °C, respectively) states using MTR_PC code. In the second stage, these parameters have been measured with an experimental method based on Inhour equation. For the cold state, calculated β_eff and Λ by MTR_PC code are 0.008315 and 30.190 μs, respectively. In the hot state, these parameters being 0.008303 and 33.828 μs, respectively. The measured β_eff and Λ for the cold state (reactor power in the range of 100–200 W) being 0.008088 and 32.001 μs, respectively. The calculated and measured values are in good agreement. Relative percent errors are about 2.8% for β_eff and 5.7% for Λ which are smaller than the other reported results. In the third stage of the research, variations of β_eff and Λ vs. fuel enrichment are investigated in cold and hot states. Comparative analysis shows that both β_eff and Λ increase as fuel enrichment decreases. However, the variation rate of β_eff is not the same in the two conditions. β_eff in the hot state is larger than that calculated in the cold state when fuel enrichment is more than 83.91%, while the situation is vice versa for the enrichments smaller than the aforementioned value. Calculated neutron generation time shows normal behavior for all different fuel enrichments. All variables involved in kinetic parameters calculations (i.e., neutron fission cross section, fuel enrichment, etc.) are investigated theoretically to evaluate the results of calculations in cold and hot states. Variations of β_eff and Λ with fuel burnup are also studied.     

Monte Carlo simulation of Feynman-α and Rossi-α techniques for calculation of kinetic parameters of Tehran Research Reactor

Noise analysis techniques including Feynman-α (variance-to-mean) and Rossi-α (correlation) have been simulated by MCNP computer code to calculate the prompt neutron decay constant (α₀), effective delayed neutron fraction (β_eff) and neutron generation time (Λ) in a subcritical condition for the first operating core configuration of Tehran Research Reactor (TRR). The reactor core is considered to be in zero power (reactor power is less than 1 W) in the entire simulation process. The effect of some key parameters such as detector efficiency, detector position and its dead time on the results of simulation has been discussed as well. The results of proposed method in the current study are validated against both the experimental data and the results of MTR_PC computer code.     

Ion irradiation induced order-to-disorder transformations in δ-phase Sc4−xZr3+xO12+x/2

The purpose of this study is to investigate the role of stoichiometry on crystal structure transformations in derivative fluorite compounds known as delta (δ) phase. In this study, polycrystalline δ-phase ceramic pellets were prepared with stoichiometries given by Sc_4−xZr_3+xO_12+x/2 (x = 0, 0.77 and 1.20)_. The pressed and polished pellets were then irradiated under cryogenic conditions with 200 keV Ne⁺ ions to fluences ranging from 1-5 × 10¹⁴ Ne/cm². An order-to-disorder (O-D) transformation was observed for all compositions, as determined using grazing incidence X-ray diffraction (GIXRD). However, the transformation threshold dose was found to systematically decrease with increasing ZrO₂ content: ∼0.2, ∼0.16, and ∼0.08 dpa for Sc_4−xZr_3+xO_12+x/2 with x = 0, 0.77, and 1.20, respectively. These irradiation-induced phase transformation results are discussed in terms of the crystal structure of the δ-phase.     

Incident photon energy and Z dependence of L X-ray relative intensities

The intensity ratios, I_Lk/I_Lα1 (k = l, η, α₂, β₁, β_2,15, β₃, β₄, β_5,7, β₆, β_9,10, γ_1,5, γ_6,8, γ_2,3, γ₄), have been evaluated for elements with atomic number 36 ? Z ? 92 at incident photon energies ranging E_L1 < E_inc ? 200 keV using currently considered to be more reliable theoretical data sets of different physical parameters, namely, L_i (i = 1-3) subshell photoionization cross sections based on the relativistic Hartree-Fock-Slater model, the X-ray emission rates based on the Dirac-Fock model, and the fluorescence and Coster-Kronig yields based on the Dirac-Hartree-Slater model. At incident photon energies above the K-shell ionization threshold, the contribution to the production of different L X-ray lines due to the additional L_i (i = 1-3) subshell vacancies created following decay of the primary K-shell vacancies have also been included in the present calculations. The important features pertaining to dependence of the tabulated intensity ratios on the incident photon energy and atomic number have been discussed.     

Uncertainty evaluation of calculated and measured kinetics parameters of Tehran Research Reactor

Effective delayed neutron fraction β_eff and neutron generation time Λ are important factors in reactor physics calculation and transient analysis. In the first stage of this research, these kinetics parameters have been calculated for two states of Tehran Research Reactor (TRR), i.e. cold (fuel, clad and coolant temperature 20 °C) and hot (fuel, clad and coolant temperature 65, 49 and 44 °C, respectively) states using MTR_PC computer code. The ratio of (β_eff)_i/(β_eff)_core plays an important role in reactivity accident analysis codes. This parameter and its contribution to effective delayed neutron fraction from each nucleus have been calculated in cold and hot reactor states. Uncertainty of effective delayed neutron fraction is evaluated in terms of following four quantities; basic delayed neutron constants, delayed neutron spectra, energy dependence of delayed neutron yield (ν_d) and fission cross-section of ²³⁵U and ²³⁸U. In the second stage, these parameters have been measured with an experimental method based on Inhour equation. The calculated and measured values are in good agreement. Relative Percent Errors (RPEs) are 2.8% for β_eff and 5.7% for Λ in the cold state.     

Absolute measurement of βeff based on Feynman-α experiments and the two-region model in the IPEN/MB-01 research reactor

A new methodology for absolute measurement of the effective delayed neutron fraction β_eff based on Feynman-α experiments and the two-region model was developed. This method made use of Feynman-α experiments and the two-region model. To examine the present methodology, a series of Feynman-α experiments were conducted at the IPEN/MB-01 research reactor facility. In contrast with other techniques like the slope method, Nelson-number method and ²⁵²Cf-source method, the main advantage of this new methodology is to obtain β_eff with the required accuracy and without knowledge of any other parameter. By adopting the present approach, β_eff was measured with a 0.67% uncertainty. In addition, the prompt neutron generation time, Λ, and other parameters, was also obtained in an absolute experimental way. In general, the measured parameters are in good agreement with the values found from frequency analysis experiments. The theory–experiment comparison for the β_eff measured in this work shows that JENDL3.3 presented the best agreement (within 1%). The reduction of the ²³⁵U thermal yield as proposed by Okajima and Sakurai is completely justified according to the β_eff measurements performed in this work.     

Calculation and measurement of kinetic parameters of Pakistan Research Reactor-1 (PARR-1)

Rossi-Alpha (β_eff/Λ) for critical reactor measured experimentally by noise analysis technique at PARR-1 core at 35.26 full power days burn up. In noise analysis technique the inherent reactivity fluctuations are taken as input to reactor system and the neutron density population fluctuations are considered as output of the reactor system. The auto power spectral density of the linear channel is taken and used to find out the break frequency by non-linear least square fitting method, which leads to β_eff/Λ = 161.45 s⁻¹. Calculations were performed with the help of computer codes WIMSD/4 and CITATION. The calculated β_eff/Λ = 161.07 s⁻¹ at 35.26 full power days burn up. The measured and calculated values for Rossi-Alpha are in good agreement within 0.235% of error.     

The δ′/δ phase transition in hafnium hydride and deuteride

Bulk samples of hafnium (Hf) hydride and deuteride were prepared and the thermal properties, heat capacity (C_P) and thermal conductivity (κ) were measured. In the C_P–temperature curves for both samples, typical lambda-type peaks were observed at around 350 K, which was due to the second-order phase transition from the δ′-phase to the δ-phase. In Hf hydride, it is considered that the δ′-phase and the δ-phase consist of regularly arranged and randomly arranged hydrogen atoms, respectively. Therefore, it can be said that the δ′/δ phase transition observed in both Hf hydride and deuteride is an order–disorder phase transition. The values of κ as well as C_P changed significantly at around the phase transition temperature.     

Proton induced L-shell X-ray production cross-sections for Pb in the energy range 225–400 KeV

The L-shell X-ray production cross-sections in lead (Pb) by proton impact over the energy range 225–400 keV, with an interval of 25 keV, have been measured. The thick target X-ray yields have been obtained using a HPGe detector. The experimental results for σ_L1, σ_Lα, σ_Lβ and σ_Lγ have been compared with perturbed stationary state theory with relativistic (R), energy loss (E) and Coulomb (C) corrections (ECPSSR theory). The comparison of L_α, L_β and L_γ, X-ray production cross-sections shows a fairly good agreement, except at the lowest energy. The L₁ X-ray production cross-sections are higher by ≈ 20–30% than their theoretical estimates.     

Structure design on improving injection performance for venturi scrubber working in self-priming mode

The venturi scrubber working in self-priming mode is one of the most efficient gas cleaning devices to remove the radioactive particles and gases from gaseous stream during severe accident in nuclear power plant. This paper focus on improving injection performance in a split type self-priming venturi scrubber, the static pressure distributions at gas and liquid channels in the scrubber are studied emphatically, the experimental results indicate that pressure at the center of nozzle exit is lower than at the wall, and the variation laws in radial are different with increasing gas velocity. When the average gas velocity at throat U_avg = 64.3 m/s, the static pressure difference between center and wall is 2.1 KPa; with the increase of gas velocity, pressure at centre and wall reduce gradually and the pressure difference become significantly, when the average gas velocity U_avg = 225.8 m/s, pressure at the center is lower 23.2 KPa than at the wall, relative deviation is about 45.6%. However, when U_avg ≥ 230 m/s, the static pressure is not continue to decrease but reverse to recover with increasing gas velocity, and recovery rate at the wall is greater than at the center. The condition before the transition point (U_avg < 230 m/s) is defined as velocity dominate area, in this area, pressure will always decrease with increasing gas velocity; the condition after the point (U_avg ≥ 230 m/s) is defined as resistance dominate area, while pressure in this area will reverse to recover, the venturi scrubber design should be ensured in velocity dominate area. The injection performance of self-priming venturi scrubber is closely relate to pressure distribution characteristics at nozzle exit, in condition of no injection or injecting air, pressure at liquid channel is consistent with the pressure at the wall of nozzle exit, which is higher than the average static pressure; when injecting water, an additional pressure increment will generate at liquid channel duo to the momentum exchange between gas and liquid, and lead to the effective pressure difference for injection reduce further. On this occasion, the influence of liquid channel area and resistance coefficient on injection performance become important, increase liquid channel area is effective for improving injection flow rate.     

L1 and L2 sub-shell fluorescence yields for elements with 64 ? Z ? 70

The L₁ and L₂ sub-shell fluorescence yields have been deduced for elements with 64 ? Z ? 70 from the L_k(k = l, α, β_1,4, β_3,6, β_2,15,9,10,7, γ_1,5 and γ_2,3,4) X-ray production cross sections measured at 22.6 keV incident photon energy using a spectrometer involving a disc type radioisotope of Cd¹⁰⁹ as a photon source and a Peltier cooled X-ray detector. The incident photon intensity, detector efficiency and geometrical factor have been determined from the K X-ray yields emitted from elemental targets with 20 ? Z ? 42 in the same geometrical setup and from knowledge of the K shell cross sections. The present deduced ω₁(exp) values, for elements with 64 ? Z ? 70, are found to be in good agreement with those tabulated by Campbell (J.L. Campbell, Atom. Data Nucl. Data Tables 95 (2009) 115), where as these are, on an average, higher by 19% and 24% than those based on the Dirac-Hartree-Slater model (S. Puri et al., X-ray Spectrometry 22 (1993) 358) and the semi-empirical values compiled by Krause (M.O. Krause, J. Phys. Chem. Ref. Data 8 (1979) 307), respectively. The present deduced ω₂(exp) values are found to be in good agreement with those based on the Dirac-Hartree-Slater model and are higher by up to ∼13% than the semi-empirical values for the elements under investigation.