Kinetics of deuterium permeation through Zircaloy-4 in the 623–773 K temperature range

Under normal operating conditions in nuclear pressurized water reactors, tritium produced by ternary fission occurring within the uranium fuel may cross the whole cladding in zirconium alloy before being released in primary water during operation, or in containers during transportation and storage. The study aims at identifying and quantifying the rate-limiting steps of this permeation process by using deuterium as isotopic tracer for tritium. A dedicated permeation device revealed that, at 773 K, deuterium permeation kinetics from the metal was limited by the surface recombination reaction. In association with gaseous deuterium charging and Thermal Desorption Spectrometry, the apparent activation energy of the deuterium desorption showed that the permeation device induced stress and strain in the specimens. A stress-free Zircaloy-4 exhibited an apparent activation energy around 240 kJ mol^?1 it dropped down to around 140 ± 10 kJ mol^?1 when under stress, in the 623 K–773 K temperature range.     

Deuterium absorption properties of V85Ni15 and evidence of isotope effect

The pressure-composition absorption isotherms of deuterium in an alloy with nominal composition V₈₅Ni₁₅ were measured between 87 and 400 °C for pressures up to ≈17 bar. For T ≤ 144 °C one observes the occurrence of a solid solution α phase for D/M < 0.15, the coexistence of α and β phase up to D/M ≈ 0.5 and a subsequent change to a different phase for higher deuterium concentrations. For temperatures higher than 200 °C only a solid solution with a deuteration enthalpy ΔH_deutr = 47 ± 2 kJ/mol is detected. The critical temperature of this V-Ni alloy (144 °C ≤ T*≤200 °C) is much higher than that of pure V (100 °C). Moreover, well above the critical temperature, one can observe a “normal” isotope effect, i.e. the equilibrium pressure of the V₈₅Ni₁₅-H system is higher than that of V₈₅Ni₁₅-D.     

The study of deuterium permeability of film-forming inhibitors with the addition of fullerenes

In this work, the results of the hydrogen permeability study of a composite film-forming inhibitor are considered. Film-forming inhibitor consists of polyether urethane and synthesized fullerenes C60 and C70 in pure form. Two types of samples were used: uncoated and coated stainless steels with composite polyether urethane/fullerene varnish. The experimental work was based on the study of the dependence of the permeation reduction factor on the temperature in the reactor. For the coated sample, the minimum temperature was 623 K at which the deuterium flux was registered. Here we assume that at temperatures below 573 K the output pressure caused by the deuterium flow through the sample is less than 10^?10 Pa. The rate of steady-state flow through a coated sample is significantly lower than for an uncoated one at temperatures 573–673 K. The deuterium penetration rates through the two samples increase and reach similar stationary values starting at 723 K.     

Rate-limiting step of the deuterium desorption kinetics from Zircaloy-4 oxidized in PWR light primary water

This study aims at identifying the rate-limiting step and quantifying the kinetic constants of diffusion and deuterium desorption from a Zircaloy-4 alloy oxidized in light primary water. Secondary Ion Mass Spectrometry deuterium concentration profiles in ZrO_2, combined with finite elements simulations, reveal that the deuterium desorption from an oxidized Zircaloy-4 alloy is kinetically controlled by a mixed regime of surface recombination and diffusion in the oxide in the 600 K–1000 K temperature range. At lower temperatures, desorption is controlled by the deuterium diffusion in the oxide layer whereas at higher temperatures the surface recombination reaction dominates.     

Studies on the kinetics of catalytic combustion of deuterium using 0.5% platinum loaded on Dixon ring catalyst

When hydrogen isotopes are present in stoichiometric ratio of 2:1 with oxygen in inert gas such as helium, catalytic combustion is the most promising option to reduce the concentration of hydrogen isotopes and to minimize the associated safety hazards. This is the case, when deuterium and oxygen is formed during radiolysis of heavy water in moderator circuit of Pressurized Heavy Water Reactors (PHWR) and mixed with helium in the cover gas system. In order to design the catalytic reactor for recombination of deuterium and oxygen, the data on catalytic combustion kinetics under the similar process conditions are essential. However, the catalytic combustion data is generally reported for combustion of hydrogen in air, where oxygen is available in excess. The studies on the kinetics of catalytic combustion of deuterium where oxygen is present in stoichiometric ratio of 2:1 in an inert gas medium such as helium, is very scarce. In the present study, the multi-step reaction mechanism of catalytic combustion of hydrogen in presence of platinum catalyst is analyzed for the present process conditions. Based on the analysis, a simple rate expression is proposed for the present process conditions of catalytic combustion of deuterium. Further, 0.5% platinum catalyst is prepared on a stainless steel Dixon ring support with an objective to achieve better heat transfer characteristics and lesser reduction in the catalytic activity due to water adsorption. The kinetic data is generated using a differential packed bed reactor operating in a closed loop. The experiments were conducted at different temperatures using a stoichiometric mixture of deuterium and oxygen in helium. The rate constant for the above proposed model is estimated based on the experimental data at different temperatures. Further, the activation energy and frequency factor are determined and the activation energy for the present catalyst is found to be on the lower side in comparison to literature data.     

Degradation mechanisms of SrBi2Ta2O9 ferroelectric thin film capacitors during forming gas annealing

Abstract

The effects of annealing in forming gas (5% hydrogen, 95% nitrogen; FGA) are studied on spin coated SrBi₂Ta₂O₉ (SBT) thin films. SBT films on platinum bottom electrode are characterized with and without platinum top electrode by Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES), High Temperature X-Ray Diffraction (HT-XRD) and Secondary Ion Mass Spectrometry (SIMS).

High Temperature X-Ray Diffraction (HT-XRD) of blanket Ti/Pt/SBT films in forming gas revealed that the bismuth layered perovskite structure of the SBT is stable up to approx. 500°C. SIMS analysis of Pt/SBT/Pt samples annealed in deuterated forming gas (5% D₂, 95% N₂) showed that the hydrogen accumulates in the SBT layer and at the platinum interfaces next to the SBT. After FGA of blanket SBT films, tall platinum-bismuth whiskers are seen on the SBT surface.

Performing the FGA of the whole Pt/SBT/Pt/Ti stack, two different results are found. For the samples with a high temperature annealing (HTA) step in oxygen after top electrode patterning, top electrode peeling is observed after FGA. For the samples without a HTA step after top electrode patterning, no peeling is observed after FGA.     

Transport of hydrogen and deuterium in the reduced activation martensitic steel ARAA

Advanced reduced activation alloy (ARAA) is a reduced activation ferritic/martensitic (RAFM) steel under development at the Korea Atomic Energy Research Institute. The transport of hydrogen and deuterium in ARAA was investigated in an elevated temperature range of 250–600 °C. A continuous-flow method, a time-dependent gas-phase technique, was used for the measurements. Complete sets of transport parameters (permeability, diffusivity, solubility, trap site density, and trapping energy) of hydrogen and deuterium in ARAA were successfully obtained. We show that appreciable trapping effects are observed only at low temperatures (250–350 °C) and that the isotope effect ratio for the diffusivity differs from the classical prediction. However, the measured values of permeability, effective diffusivity, and effective solubility of ARRA were within the range of results reported for other RAFM steels.     

Evaluating the hydrogen isotope absorption/diffusion coefficient of CVD-SiC at high temperature

Deuterium diffusion coefficient measurements of CVD-SiC were carried out using a solubility and diffusivity measurement apparatus to investigate the permeation mechanism of the hydrogen isotope through CVD-SiC. Experiments were conducted with thin-sheet-type samples with thicknesses of 0.1 mm, 1 mm, and 2 mm at 1073–1183 K. Total amount of occluded gas into or released gas from different thickness but same weight sample were expected to be the same, but unexpectedly differed by more than 50%. As the release rates after sufficient time had passed were almost the same, and the 1-mm-thick sample had twice the surface area of the 2-mm-thick sample, the measurements were probably affected by adsorbed gas on the surface. The value of D/L² (the diffusion coefficient divided by the square of the thickness), obtained by fitting to the theoretical formula but ignoring the early phase of discharge, was in good agreement for samples of different thickness at the same temperature, and was more than 5 orders of magnitude smaller than that obtained from the permeability measurement experiments. Therefore, we believe that the deuterium permeation through CVD-SiC is primarily dependent on the permeation rate through the grain boundaries.     

液态锂铅合金的氚释放行为

为了完成聚变堆液态锂铅包层鼓泡提氚系统的工程设计和建造,以金属与氢的作用理论为基础,建立了氚从液态锂铅中的动力学释放行为的数学模型.计算和分析了温度、饱和器氚分压、氦流量对解吸器顶部气相中的氚分压的影响以及氚在液态锂铅中的传质系数、解吸率和吸附率.结果表明:在633～723 K的解吸温度范围内,氚从液态锂铅到气相的整个释放过程虽然包含了氚在熔融合金气泡中的扩散与对流、氚通过与气-液界面相连合金层的扩散、在界而发生的氚原子重组多相反应、氚通过气相边界层的扩散和气相中氚的扩散与对流5个子过程,但起决定作用的是氚在合金内的扩散和气.液界面的多相反应重组,其他子过程意义不大.     

氘气处理消除光纤氢敏感性

通过分析光纤的过氧基缺陷,用氘气对成品低水峰光纤进行处理,以降低光纤的氢敏感性。结果表明,氘气处理后光纤在1383nm的氢损值小于0.01dB/km,并且这种抗氢损能力不随时间变化而变化,从而保证了光纤长期使用过程中的稳定性。