Transport properties of I, Te and Xe in thoria-urania SIMFUEL

Diffusion properties for volatile fission products iodine and tellurium, and gaseous product xenon in a solid solution of thoria-2 mol% urania doped with fission products for simulating 2 at.% burnup were obtained by studying the release kinetics of the species from trace-irradiated fuel samples at different temperatures using post-irradiation annealing technique. Bulk diffusion coefficients for Xe, I and Te were evaluated in a well-defined powder sample of particle size in the range of 37-45 μm (25 m² kg⁻¹ BET surface area) with 97% of theoretical density. Temperature dependences of the apparent diffusion coefficients of Xe, I and Te derived from this study could be expressed in the form of Arrhenius equations for the respective cases as ln (s⁻¹) = −(19,480 ± 3300)/T − 9.3 ± 2.2 and ln (s⁻¹) = −(31,234 ± 3000)/T − 3.7 ± 2.0, (1273 ? T/K ? 1773) and ln (s⁻¹) = −(22,755 ± 1364)/T − 0.003 ± 0.775, 1700 ? T/K ? 1800. For Xe diffusion the activation energy and frequency factor are 189 kJ mol⁻¹ and 0.997 s⁻¹, respectively. For I and Te the activation energy values are 162 and 260 kJ mol⁻¹, respectively. The respective frequency factors for I and Te are 9.1 × 10⁻⁵ and 2.5 × 10⁻² s⁻¹. On comparison with the reported data in pure urania and thoria matrices a lowering of activation energy for all three species was observed in case of the fission product doped matrix. On the other hand the frequency factor has increased only in the case for diffusion of Xe. This suggests different mechanisms of transport for Xe and volatile fission products I and Te in the fuel matrix.     

Vapour pressure and standard enthalpy of sublimation of H3BO3

A horizontal thermal analysis instrument was adapted as a transpiration apparatus for the measurement of vapour pressure of solid boric acid, H₃BO₃. The experimental parameters necessary for establishing a dynamic isothermal congruent vapourisation equilibrium of H₃BO₃ were identified. Using these optimized transpiration experiments, the vapour pressures were measured in the temperature range 326-363 K. The temperature dependence of the measured values of vapour pressures could be expressed using the expression, log(p/Pa) = 26.83(±0.09) − 9094(±246)/T (K). The standard enthalpy of sublimation, , of H₃BO₃ was estimated to be 174.1 ± 4.7 kJ mol⁻¹ at the mean temperature of the present measurements, viz., 345 K.     

Dating of aragonite fossil shell by ESR for paramagnetic species assignment of Mae Moh basin

Electron spin resonance (ESR) spectroscopy technique has been employed to date the aragonite freshwater fossil shells in bottom sediments collected from Mae Moh basin of northern Thailand in the southwest margin of the coal pit. The samples were given an accumulated dose (AD) of 1100.46 ± 52.72 Gy by the additive irradiation method. The dose response of the ESR signals were found to be suitable for an age determination using a signal at g = 2.0016 corresponding to . The ESR signal growth curve on additional γ irradiation has been best fitted by a linear saturation function. Based on this model, the accumulated dose value for dating is obtained. The ESR age of the aragonite fossil shells was found to be about 13.02 ± 1.03 Ma. The results show that the ESR age within the Middle Miocene, Mae Moh Group of the geological time scale, which agreed with the stratigraphic level of the fauna.     

Radiation induced defects in BaBPO5:Ce and their role in thermally stimulated luminescence reactions: EPR and TSL investigations

Defect centers induced by gamma irradiation in Ce doped BaBPO₅ were investigated using EPR spectroscopy. From EPR studies, three phosphorous centered radicals were characterized on the basis of observed ³¹P hyperfine splitting and g values as , and radicals. In addition to this, two types of boron oxygen hole centers (BOHC) and O⁻ were also formed at room temperature. An intense broad signal in sample annealed in argon (g_⊥ = 1.9258 and g_‖ = 1.8839) was assigned to Ce³⁺ ions associated with the electron trapped at anion vacancy or nearby lattice defect. TSL studies showed two glow peaks, a relatively weaker one at 425 K and an intense one at 575 K. Spectral studies of the TSL glow peaks have shown that Ce³⁺ ion acts as emission center. From the temperature dependence of the EPR spectra of gamma irradiated samples, the glow peaks at 425 K and 575 K were attributed to thermal destruction of /O⁻ and BOHC, respectively, by trapping of electrons from elsewhere. The energy released in electron hole recombination process is used for the excitation of Ce³⁺ ions resulting in these glow peaks at 425 K and 575 K. The spectral studies of the TSL glow peaks have shown emission at 330 nm indicating Ce³⁺ acts as the luminescent centre. The trap depth and the frequency factor for the 425 K and 575 K peaks were determined using different heating rates method.     

Reflection properties of small hydrocarbons impinging on tungsten and carbon surfaces

Sticking coefficients of deuterium from are quantified on fusion relevant plasma sprayed tungsten and carbon fibre composite in the incident energy range from about 0-100 eV. The samples that were cut from ASDEX-Upgrade tiles are exposed to a beam of of specific incident energy, E_inc, in the tandem mass spectrometer BESTOF in Innsbruck. Nuclear reaction analysis is performed ex-situ at IPP Garching for the quantification of deuterium content. The deuterium content difference measured on a spot before and after ion-beam exposure of the sample is assigned to the above mentioned species of hydrocarbon molecules sticking on the surface, allowing the calculation of the sticking probability of a specific deuterated molecular ion. The sticking coefficient, S, is found to depend on the incident energy and shows a maximum of about S ∼ 0.4 around E_inc = 30 eV on CFC and about S ∼ 0.1 near E_inc = 20 eV in case of PSW.     

Analysis of oxygen potential of (U0.7Pu0.3)O2±x and (U0.8Pu0.2)O2±x based on point defect chemistry

Stoichiometries in (U_0.7Pu_0.3)O_2±x and (U_0.8Pu_0.2)O_2±x were analyzed with the experimental data of oxygen potential based on point defect chemistry. The relationship between the deviation x of stoichiometric composition and the oxygen partial pressure P_O2 was evaluated using a Kröger-Vink diagram. The concentrations of the point defects in uranium and plutonium mixed oxide (MOX) were estimated from the measurement data of oxygen potentials as functions of temperature and P_O2. The analysis results showed that x was proportional to near the stoichiometric region of both (U_0.7Pu_0.3)O_2±x and (U_0.8Pu_0.2)O_2±x, which suggested that intrinsic ionization was the dominant defect. A model to calculate oxygen potential was derived and it represented the experimental data accurately. Further, the model estimated the thermodynamic data, and , of stoichiometric (U_0.7Pu_0.3)O_2.00 and (U_0.8Pu_0.2)O_2.00 as −552.5 kJ·mol⁻¹ and −149.7 J·mol⁻¹, and −674.0 kJ · mol^-1 and −219.4 J · mol⁻¹, respectively.     

Linear free energy relationship applied to trivalent cations with lanthanum and actinium oxide and hydroxide structure

Linear free energy relationships for trivalent cations with crystalline M₂O₃ and, M(OH)₃ phases of lanthanides and actinides were developed from known thermodynamic properties of the aqueous trivalent cations, modifying the Sverjensky and Molling equation. The linear free energy relationship for trivalent cations is as , where the coefficients a_MvX, b_MvX, and β_MvX characterize a particular structural family of MvX, r_M³⁺ is the ionic radius of M³⁺ cation, is the standard Gibbs free energy of formation of MvX and is the standard non-solvation free energy of the cation. The coefficients for the oxide family are: a_MvX = 0.2705, b_MvX = −1984.75 (kJ/mol), and β_MvX = 197.24 (kJ/mol nm). The coefficients for the hydroxide family are: a_MvX = 0.1587, b_MvX = −1474.09 (kJ/mol), and β_MvX = 791.70 (kJ/mol nm).     

Standard enthalpy of formation of compounds of the Cd-Zr system

Thermodynamic properties of two intermetallic phases CdZr₂(s) and Cd₃Zr(s) in the binary Cd-Zr system have been investigated. The standard molar enthalpy of formation of CdZr₂(s) and Cd₃Zr(s) was obtained by measuring the reaction enthalpy of CdZr₂(s), Cd₃Zr(s) and Zr(s), respectively, using Cd(l) in a Calvet calorimeter. The values of of CdZr₂(s) and Cd₃Zr(s) at 298 K were found to be −(61.7 ± 1.2) kJ mol⁻¹ and −(72.3 ± 0.9) kJ mol⁻¹, respectively.     

Ga NMR and magnetic susceptibility in δ-phase of Pu1−xGax (x = 0.05, x = 0.08) alloys

⁶⁹Ga nuclear magnetic resonance spectra, line shifts (⁶⁹K) and nuclear spin-lattice relaxation rate have been measured in the 20 years aged Pu_0.95Ga_0.05 and in fresh prepared Pu_0.92Ga_0.08 alloys, stabilized δ-phase, at magnetic field of 9.4 T in the temperature range (10-500) K. The line shift and are determined correspondingly by the static and fluctuating-in-time parts of the local magnetic field that originates in transferred hyperfine coupling the Ga nuclear spin with the nearest f-electron environment of more magnetic Pu.Temperature behavior of the resonance properties is found the same in fresh Pu_0.92Ga_0.08 and aged Pu_0.95Ga_0.05 alloy. The NMR results are in favor that δ-phase of Pu_1−xGa_x alloys represents at T > 200 K the Kondo lattice, in which the localized electronic spins fluctuate independently from each other without any macroscopic coherence. The coherent state like in heavy-fermion liquids emerges in Pu_0.95Ga_0.05 below T^∗ = 200 K. A little bit higher estimate of crossover temperature T^∗ = 250 K was founded for Pu_0.92Ga_0.08.     

Vaporization behavior and Gibbs energy of formation of Rb2ThO3

The thermodynamic stability of rubidium thorate, Rb₂ThO₃(s), was determined from vaporization studies using the Knudsen effusion forward collection technique. Rb₂ThO₃(s) vaporized incongruently and predominantly as Rb₂ThO₃(s)=ThO₂(s) + 2Rb(g) + 1/2 O₂(g). The equilibrium constant K=p_Rb²·p_O2^1/2 was evaluated from the measurement of the effusive flux due to Rb vapor species under the oxygen potential governed by the stoichiometric loss of the chemical component Rb₂O from the thorate phase. The Gibbs energy of formation of Rb₂ThO₃ derived from the measurement and other auxiliary data could be given by the equation, Δ_fG°(Rb₂ThO₃,s)=−1794.7+0.42T ± .     

Magnetic and related properties of PuPdSn

A new phase PuPdSn was prepared and studied by X-ray diffraction, magnetization and heat capacity measurements, performed in the temperature range 2-300 K and in magnetic fields up to 14 T. The crystal structure determined from single-crystal X-ray data is the hexagonal ZrNiAl-type [space group ] with lattice parameters: a = 7.5057 Å and c = 4.0853 Å. PuPdSn orders antiferromagnetically at T_N = 21 K. Moreover, another antiferromagnetic-like transition takes place at 9.6 K. Above T_N the susceptibility follows a modified Curie-Weiss law with μ_eff = 1.0 μ_B, Θ_p = −14 K and χ₀ = 2.1 × 10⁻⁴ emu/mol. The low-temperature linear specific heat coefficient is small (γ ∼ 8 mJ/mol K²) pointing to well localized 5f electrons.     

Oxygen potential of (U0.88Pu0.12)O2±x and (U0.7Pu0.3)O2±x at high temperatures of 1673-1873 K

The oxygen potential of (U_0.88Pu_0.12)O_2±x (−0.0119 < x < 0.0408) and (U_0.7Pu_0.3)O_2±x (−0.0363 < x < 0.0288) was measured at high temperatures of 1673-1873 K using gas equilibrium method with thermo gravimeter. The measured data were analyzed by a defect chemistry model. Expressions were derived to represent the oxygen potential based on defect chemistry as functions of temperature and oxygen-to-metal ratio. The thermodynamic data, and , at stoichiometric composition were obtained. The expressions can be used for in situ determination of the oxygen-to-metal ratio by the gas-equilibration method. The calculation results were consistent with measured data. It was estimated that addition of 1 wt.% Pu content increased oxygen potential of uranium and plutonium mixed oxide by 2-5 kJ/mol.     

Measurement of radiation-enhanced diffusion of La in single crystal thin film CeO2

The diffusion of La, a trivalent cation dopant, actinide surrogate, and high-yield fission product, in CeO₂, a UO₂ nuclear fuel surrogate, during 1.8 MeV Kr⁺ ion bombardment over a temperature range from 673 K to 1206 K has been measured with secondary ion mass spectroscopy. The diffusivity under these irradiation conditions has been analyzed with a model based on a combination of sink-limited and recombination-limited kinetics. This analysis yielded a cation vacancy migration energy of  ∼ 0.4 eV below ∼800 K, were recombination-limited kinetics dominated the behavior. The thermal diffusivity of La in the same system was measured over a range of 873-1073 K and was characterized by an activation enthalpy of . The measurement of both the migration enthalpy and total activation enthalpy separately allows the vacancy formation enthalpy on the cation sublattice to be determined;  ∼ 1 eV. The mixing parameter under energetic heavy-ion bombardment at room temperature was measured as well and found to be ∼4 × 10⁻⁵ nm⁵/eV.     

First principle studies on the electronic structures and absorption spectra in KMgF3 crystal with fluorine vacancy

The experiments indicate that the perfect KMgF₃ crystal has no absorption in the visible range, however the electron irradiation induces a complex absorption spectrum. The absorption spectra can be decomposed by five Gaussian bands peaking at 2.5 eV (488 nm), 3.4 eV (359 nm), 4.2 eV (295 nm), 4.6 eV (270 nm) and 5.2 eV (239 nm), respectively. The purpose of this paper is to seek the origins of the absorption bands. The electronic structures and absorption spectra either for the perfect KMgF₃ or for KMgF₃: with electrical neutrality have been studied by using density functional theory code CASTEP with the lattice structure optimized. The calculation results predicate that KMgF₃: also exhibits five absorption bands caused by the existence of the fluorine ion vacancy and the five absorption bands well coincide with the experimental results. It is believable that the five absorption bands are related to in KMgF₃ crystal produced by the electron irradiation.     

The investigation of energy loss and damage in polycarbonate induced by MeV carbon clusters

Carbon cluster ions (n = 1-5) and Cl⁺, Ti⁺, Ni⁺ ions were used to bombard polycarbonate (PC) films. By comparing the electronic energy loss and the number of chromophores at a fixed wavelength, we obtained the electronic energy loss S_e of carbon cluster ions in PC.