Recombination of hydrogen and oxygen in the technical gaseous waste of nuclear power plants

The recombination of hydrogen and oxygen in technical gaseous waste of nuclear power plants in enlarged scale experiment has been studied on the basis of our previous work.¹ The catalyst and its best operating conditions for recombination of hydrogen and oxygen determined in a small scale experiment were demonstrated and tested. The results show that the data obtained in an enlarged scale experiment agreed well with that of in a small scale test. The recombination rate of H₂ and O₂ was higher than 98.3% and 99.98% respectively. After recombination, the residual concentrations of H₂ and O₂ in waste gas were O₂<3 ppm, H₂<400 ppm. The Pd-Al₂O₃ catalyst and operating conditions determined for gaseous waste processing of nuclear power plants were satisfactory.     

Radiochemical methodologies applied to determination of zirconium isotopes in low-level waste samples from nuclear power plants

The ⁹³Zr determination in low-level radioactive wastes generated at nuclear power plants is an important issue for waste disposal purpose. This paper describes an analytical methodology developed for ⁹³Zr determination based on selective separation using extractive resins associated with inductively coupled plasma mass spectrometry (ICP-MS) and liquid scintillation counting (LSC) measurements. The ⁹³Zr results obtained for waste samples were in a good agreement for both techniques and the detection limits of 0.045 μg L^?1 and 0.05 Bq L^?1 were obtained for ICP-MS and LSC techniques respectively.     

Improvements on radiochemical method for the determination of Am and Cm in typical waste streams from nuclear power plants

The determination of Am and Cm in typical waste streams from nuclear power plants using anion exchange chromatography has some drawbacks like the contamination by Pu and Po. This improved procedure solves these problems, and it has been applied with success to the analysis of Am and Cm in nuclear waste samples: ion exchange resins, ion exchange resins solidified with cement and evaporator concentrates.     

Spontaneous reductive decomposition behavior of hydrogen permanganate in water for chemical decontamination of nuclear power plants

The spontaneous reductive decomposition behavior of HMnO₄ in water as a function of the initial HMnO₄ concentration and reaction temperature was investigated. The decomposition of HMnO₄ was fast in the early stage of the reaction and thereafter slowed down significantly, regardless of the initial HMnO₄ concentration. The loss of HMnO₄ by spontaneous reductive decomposition increased with increasing reaction temperature. Based on the experimental results and the classical nucleation theory, a mathematical model was developed using a combination of two first-order reactions representing the nucleation and crystal growth of MnO₂ to predict the spontaneous reductive decomposition behavior of HMnO₄.     

Assessment of the EPDM seal lifetime in nuclear power plants

An EPDM seal was qualified for use in nuclear power plants (NPPs). The primary function of the seal is to prevent leakage of unwanted fluids and gases during long-term normal operation, as well as during postulated accidents which may occur at the end of the planned service lifetime. Tested samples were compressed between two massive metal plates (the same compression as under regular service conditions) and exposed to an accelerated ageing procedure to simulate up to 10 years of operation, including accident simulation. Mechanical properties, compression set and a gas leakage test were carried out. The minimum necessary compression to keep the required tightness under all conditions during normal service and during accident conditions was found and the service lifetime was assessed for two seal thicknesses.     

Rapid monitoring of gaseous fission products released from nuclear power stations

Rapid, in situ measurements were used for quantitative monitoring of gaseous fission products around the nuclear power stations in Taiwan. A portable high-resolution germanium detector with portable multichannel analyzer was used in the field monitoring work. The detecting unit was calibrated using activated Ar, Kr, and Xe isotopes dispersed in a large chamber to obtain absolute efficiency curve in terms of γ-counts per m³ versus gamma-ray energy. The calibrated detecting unit was brought to the nuclear power plants for in situ monitoring for both normal operation and nuclear accidental exercise. In a typical four-hour measurement, the detection limits for most Kr and Xe fission product isotopes were 0.0028%≈0.98% of the derived air concentration (DAC) imposed by the local authority. The dose rate caused by gaseous radioisotopes released from nuclear power stations and dispersed to the surroundings can be quantitatively monitored in a short period using this portable unit.     

Oxidation of nitrided si(100) by gaseous atomic and molecular oxygen

The nitridation of Si(100) by ammonia and the subsequent oxidation of the nitrided surface by both gaseous atomic and molecular oxygen was investigated under ultrahigh vacuum (UHV) conditions using X-ray photoelectron spectroscopy (XPS). Nitridation of Si(100) by the thermal decomposition of NH3 results in the formation of a subsurface nitride and a decrease in the concentration of surface dangling bond sites. On the basis of changes in the N1s spectra obtained after NH3 adsorption and decomposition, we estimate that the nitride resides about four to five layers below the vacuum-solid interface and that the concentration of surface dangling bonds after nitridation is only 59% of its value on Si(100)-(2 x 1). Oxidation of the nitrided surface is found to produce an oxide phase that remains in the outer layers of the solid and interacts only weakly with the underlying nitride for oxygen coverages up to 2.5 ML. Slight changes in the N1s spectra observed after oxidizing at 300 K are suggested to arise primarily from the introduction of strain within the nitride, and by the formation of a small amount of Si2=N-O species near the nitride-oxide interface. The nitrogen bonding environment changes negligibly after oxidizing at 800 K, which is indicative of greater phase separation at elevated surface temperature. Nitridation is also found to significantly reduce the reactivity of the Si(100) surface toward both atomic and molecular oxygen. A comparison of the oxygen uptake on the clean and nitrided surfaces shows quantitatively that the decrease in dangling bond concentration is responsible for the reduced activity of the nitrided surface toward oxidation, and therefore that dangling bonds are the initial adsorption site for both gaseous oxygen atoms and molecules. Increasing the surface temperature is found to promote the uptake of oxygen when O2 is used as the oxidant, but brings about only a small enhancement in the uptake of gaseous O-atoms. The different effects of surface temperature on the uptake of O versus O2 are interpreted in terms of the efficiency at which dangling bond pairs are regenerated on the surface at elevated temperature and the different site requirements for the adsorption of O and O2.     

Recombination proteins and telomere stability in plants

Repair of DNA damage is essential for the maintenance of the integrity and transmission of the genome in development and reproduction. Telomeres are nucleoprotein structures which protect the ends of (linear) eukaryotic chromosomes. Telomere dysfunction results in loss of this protection and the telomeres being recognised as DNA damage by the cellular DNA Damage Repair and Response (DDR) machinery, leading to senescence or cell death. Telomeric homeostasis is thus tightly controlled and many specific and non-specific proteins are involved in its regulation. Among these, DNA damage and Repair proteins contribute both to the recognition of telomere dysfunction and more surprisingly, are directly implicated in telomere homeostasis itself. Plants offer a great opportunity to study these mechanisms due to the fact that many key DNA repair and recombination proteins are non-essential in plants, in contrast to vertebrates. In the following text, after a brief summary of the current state of knowledge on telomere-specific proteins in plants, we review the DDR processes and the related proteins implicated in plant telomere stability. We focus specifically on telomere signalling and on recombination events induced by unprotected telomeres, at the origin of genome rearrangements and instability when telomere function is affected.     

Estimation of chemical exergy of solid, liquid and gaseous fuels used in thermal power plants

This paper presents the methods for the calculation of chemical exergies of coal, heavy fuel oil and natural gas that are used as fuel in conventional thermal power plants. Calculations have shown that the chemical composition of the fuel greatly influences the value of its chemical exergy. In case of coal in which carbon and hydrogen are not combined together, an increase in both carbon and hydrogen contents increases its chemical exergy value. In case of heavy fuel oils, hydrogen–carbon ratio is the most influencing parameter in the chemical exergy value. An increase in hydrogen–carbon ratio in the fuel tends to increase its chemical exergy. In case of natural gases, a decrease in lighter hydrocarbon gas contents and an increase in heavier hydrocarbon gas contents tend to increase the chemical exergy value of the fuel. High moisture and/or ash contents also tend to lower the value of the chemical exergy.     

Pilot determinations of 3H and 14C in gaseous releases from Kozloduy nuclear power plant

Methods for routine assessment of ³H and ¹⁴C content in gaseous releases from ventilation stacks of Kozloduy Nuclear Power Plant (Bulgaria) were developed. Technique for correction of incomplete desorption of tritium from exposed silica gel was proposed. The distribution and the concentrations of both nuclides in various chemical forms were constantly monitored for a period of 1 year. The results for annual normalized gaseous discharges were assessed for the fifth unit at 173 GBq/(GW.a) for ³H and 369 GBq/(GW.a) for ¹⁴C, while for the sixth unit—³H—98 GBq/(GW.a) and ¹⁴C—289 GBq/(GW.a).     

NAA for optimization of radiation shielding of nuclear power plants

The results of activation studies of concrete ingredients for shielding structures of nuclear installations in the aspect of their decommissioning are given. It is shown that for the long-lived induced radioactivity of construction mineral materials irradiated for 30 years and cooled for more than one year such radionuclides as calcium, iron, cobalt, caesium and europium are responsible. Elemental content of the binding agent and raw material components for their production is obtained by neutron activation analysis. The results show that the type of the binding agent influences to a great extent the concrete shielding activity. The concentration of the above mentioned elements should be taken into account even at the stage of nuclear power plants design. It would allow one to make a prognosis on the volume and radioactivity of wastes as on the radioactivity effect felt by the staff engaged in the decommissioning.     

Influence of gaseous hydrogen on the hydrogen transfer reaction between phenanthrene and hydrogen donors

Transfer hydrogenation of phenanthrene was performed in the presence of superbases or strong acids and gaseous hydrogen. The influence of hydrogen on the yield of these reactions was discussed with respect to the mechanism of hydrogen transfer.     

Automated separation and analysis of krypton-85 from low-volume gaseous effluent of nuclear power plant

Journal of Radioanalytical and Nuclear Chemistry - Based on the requirements of the lower detection limit for the low-volume gaseous effluent, we have designed an automatic separation apparatus of...     

Recombination of carbon monoxide and oxygen atoms

The recombination of carbon monoxide and oxygen atoms was studied in reflected shock waves in H₂:O₂:CO:Ar = 0.1:1:24:75 with 1300 < T₅ 2200 K and 2 < P₅ < 4 atm. Reaction progress was monitored by observations of the carbon monoxide flame spectrum near 435 nm and carbon dioxide thermal emission near 4.2 μm. Data analysis was accomplished with the aid of computer modeling using a 27-reaction mechanism. Computer modeling experiments also showed that these measurements were sensitive primarily to the rate of the reaction CO + O + M = CO₂ + M and only slightly sensitive to the rates of other reactions. The best fit to the data was achieved with a rate constant for this reaction of 7.7 × 10^?35 exp[19 kJ/RT] cm⁶ s for the temperature range of these experiments. Correlation of this result and previous data covering the temperature range 250 < T < 11,000 K confirms that this recombination reaction is governed by a nonadiabatic curve crossing with an activation barrier of about 20 kJ and subsequent deactivation of a singlet CO₂ molecule.     

Replacing the hydrogen in the intermolecular hydrogen bond of the cyanuric acid-bipyridyl adduct by Ag(I)

A complex between cyanuric acid (CA), 4,4′-bipyridyl (BP) and Ag(I), with the composition, [Ag₂(C₃H₂N₃O₃-κN)₂ (C₁₀H₈N₂-κN)] has been prepared. Crystal structure analysis shows that it has a chain structure in which the CA molecules are linked to the BP units through silver atoms by the formation of N-Ag-N bonds, wherein one of the hydrogens of CA is replaced by Ag(I), showing thereby the chains connected to one another by N-H...O hydrogen bonds formed between the CA molecules. This intermolecular chain structure resembles the chain structure of the CA.BP adduct where CA-BP-CA chains formed by N-H...N hydrogen bonds are linked to one another by N-H...O hydrogen bonds between the CA molecules.     

The microdetermination of carbon dioxide,oxygen, carbon monoxide,and hydrogen in gaseous mixtures Krogh method

Summary The analysis of gases by theKrogh technique of entrapping a bubble under glycerol and exposing it to selective absorbents has been examined to assess its value as a means of determining quantitatively oxygen, carbon dioxide, carbon monoxide and hydrogen in volumes of sample of the microlitre order. The method, after modifications to accommodate for non-specificity of the absorption reagents, has given satisfactory performance, and it possesses the additional advantage of simplicity of apparatus.

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Zusammenfassung Das gasanalytische Verfahren vonKrogh, wonach eine Gasblase in Glycerin eingeschlossen und unter dem Mikroskop der Einwirkung selektiver Absorptionsmittel ausgesetzt wird, wurde geprüft, um seine Eignung zur quantitativen Bestimmung von Sauerstoff, Kohlendioxyd, Kohlenmonoxyd und Wasserstoff in Proben der Größenordnung von Mikrolitern festzustellen. Das Verfahren wurde modifiziert, um es der Verwendung nicht spezifischer Absorptionsreagenzien anzupassen, und läßt sich nun in befriedigender Form durchführen. Es bietet den zusätzlichen Vorteil der Einfachheit in apparativer Hinsicht.

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Résumé La technique d'analyse de gaz deKrogh qui consiste à emprisonner une bulle de gaz sous du glycerol et à l'exposer à des réactifs absorbants sélectifs a été éprouvée pour le dosage de l'oxygène, du gaz carbonique, de l'oxyde de carbone et de l'hydrogène sur des échantillons dont le volume est de l'ordre de grandeur du microlitre. La méthode a fourni des résultats satisfaisants après certaines modifications destinées à tenir compte de la non spécificité des réactifs absorbants; elle présente l'avantage complémentaire de la simplicité de l'appareillage mis en oeuvre.

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The author wishes to thank Mr.F. J. Woodman who initiated this work, and Mr.I. Waide for technical co-operation. This paper is published by permission of the Managing Director, United Kingdom Atomic Energy Authority (Industrial Group).