Effect of the presence of In and Sn in the oxygen chemistry in molten 44.5% lead-55.5% bismuth alloy

The oxygen activity and its control is a key parameter in the use of molten lead-bismuth eutectic LBE in accelerator-driven systems (ADS) reactors. The presence of pollutants in the molten alloy, such as metallic impurities dissolved from the structural material or from other sources, can modify the oxygen chemistry in the molten alloy. For this reason, the oxygen activity in molten LBE has been studied under the presence of In and Sn as a metallic impurities. All the experiments were performed with a shift of the covering gas from a reductive environment (Ar + 10% H₂) to air (20% O₂). These covering gas conditions were used to enable measurement of the electrochemical potential of the sensor in a low oxygen environment and under oxygen saturation conditions of the molten alloy (Me/LBE). All of the tests were performed at 500 °C and in stagnant conditions in an autoclave.     

Active control of oxygen in molten lead-bismuth eutectic systems to prevent steel corrosion and coolant contamination

The thermodynamic basis for controlling oxygen level in lead-bismuth to prevent steel corrosion and coolant contamination is examined. The operational conditions, including the thermodynamic activity of oxygen, cover gas oxygen partial pressure, mixtures of H₂ and H₂O (steam) to obtain such low oxygen partial pressure (<10⁻²⁴ atm or around 10⁻⁶ wt% in lead-bismuth), and the voltage signals of one type of oxygen sensors (with a solid electrolyte and molten bismuth reference electrode) are calculated. These results provide the guidance to implement the oxygen control technique.     

Oxygen measurements in stagnant lead-bismuth eutectic using electrochemical sensors

Sensors are the major part of an active oxygen control system (OCS) to be used in ADS reactors employing lead bismuth eutectic (LBE). We tested Pt/air and Bi/Bi₂O₃ probes based on yttria-stabilized zirconia (YSZ) solid electrolytes. The sensors were calibrated by evaluating the electromotive force (EMF) - temperature dependencies in oxygen un-/saturated stagnant LBE compared to the van’t-Hoff’s isotherm. Also, probe kinetics while changing the H₂/H₂O ratio was studied. Typical, reproducible curves are presented confirming attainment of oxygen equilibrium between the fluids. The sensor outputs are deterministic, predictable. Exceptional small drifts were due to interfacial kinetics, not to the sensors behavior. Simultaneous testing of several probes in one melt was performed. The sensors seemed to be qualified for large scale use.     

铅铋合金中Bi/Bi_2O_3型氧传感器准确性及稳定性测试研究

液态铅铋合金(LBE)中溶解氧浓度的精确测量是实现LBE中氧浓度控制的前提。本文用一自主研制的Bi/Bi2O3型氧传感器来测量LBE氧浓度,在静态氧饱和的LBE中分别进行了准确性及稳定性测试。准确性测试结果表明,在340~480℃范围内氧传感器电动势实验曲线随温度的变化与理论曲线一致,电动势绝对误差最大为-2.6 mV;稳定性测试结果表明,在450℃、50h内电动势绝对误差为-1.4mV,波动为4mV。     

Impurities and oxygen control in lead alloys

The control of the impurities is of major interest for ensuring adequate and safe operation of lead alloys facilities from the viewpoint of the corrosion phenomenon. Specific methods have to be implemented for effective control of the liquid lead-bismuth eutectic quality to the required specifications, as for instance: dissolved oxygen monitoring, dip sampling system, analytical techniques for impurities measurement. Even though the oxygen control in the static facility BIP proved difficult, a better knowledge of kinetics behaviour of the oxygen is acquired. Oxygen sensors gave results in agreement with the theory during the tests achieved on the BIP and on the COLIMESTA facilities. The dip sampler was validated on static device: it allows an effective sampling of the liquid metal melt and an easy separation of the melt from the sampling device when cold. The set of analytical techniques for the measurements of metallic impurities is efficient as well, except for the nickel element, for which the method of analysis with atomic absorption spectroscopy coupled with spiking method should allow the lower detection limit to be decreased below the 5 μg/g as for the iron impurity.     

Oxide layer stability in lead-bismuth at high temperature

Materials protection by ‘in situ’ oxidation has been studied in stagnant lead-bismuth, with different oxygen levels (H₂/H₂O ratios of 0.3 and 0.03), at temperatures from 535 °C to 600 °C and times from 100 to 3000 h. The materials tested were the martensitic steels F82Hmod, EM10 and T91 and the austenitic stainless steels, AISI 316L and AISI 304L. The results obtained point to the existence of an apparent threshold temperature above which corrosion occurs and the formation of a protective and stable oxide layer is not possible. This threshold temperature depends on material composition, oxygen concentration in the liquid lead-bismuth and time. The threshold temperature is higher for the austenitic steels, especially for the AISI 304L, and it increases with the oxygen concentration in the lead-bismuth. The oxide layer formed disappear with time and, after 3000 h all the materials, except AISI 304L, suffer corrosion, more severe for the martensitic steels and at the highest temperature tested.     

Preliminary study on nano- and micro-composite sol-gel based alumina coatings on structural components of lead-bismuth eutectic cooled fast breeder reactors

In order to protect the structural components of lead-bismuth eutectic cooled fast breeder reactors from liquid metal corrosion, Al₂O₃ nano- and micro-composite coatings were developed using an improved sol-gel process, which includes dipping specimens in a sol-gel solution dispersed with fine α-Al₂O₃ powders prepared by mechanical milling. Accelerated corrosion tests were conducted on coated specimens in liquid lead-bismuth eutectic at 500 °C under dynamic conditions. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses revealed that the coatings are composed of α-Al₂O₃ and they are about 10 μm thick. After the corrosion tests, no spallation occurred on the coatings, and neither Pb nor Bi penetrated into the coatings, which indicates that the coatings possess an enhanced dynamic LBE corrosion resistance to lead-bismuth eutectic corrosion. The nano-structured composite particles integrated into the coatings play an important role in achieving such superior lead-bismuth eutectic corrosion resistance.     

Phase diagram of the Rb-O system and disproportionation of rubidium suboxide

The phase diagram of the Rb-O system has been examined up to 28 at% oxygen and below 200°C. A eutectic point was found between rubidium and a rubidium suboxide (either Rb₆O or Rb₉O₂) at 10 at% oxygen and − 14°C. Three peritectic reactions were found: above 12 at% oxygen at − 11°C, above 14 at% oxygen at 20°C, and above 18 at% oxygen at 116°C. However, the composition of the rubidium suboxide that reveals the peritectic reaction could not be obtained. Oxygen solubility in rubidium above the melting point was equal to or greater than 3 wt%. With increasing oxygen concentration in the Rb-O mixture, the examination became more difficult. This difficulty appeared to be due to an intrinsic property of the Rb-O system, i.e. disproportionation of rubidium suboxide in the system. These results are in general agreement with those of Simon [4] but not with those of Touzain [3].     

Models of liquid metal corrosion

In the present study, models for liquid metal corrosion are reviewed and their applications in nuclear reactor engineering are discussed. The paper presents mathematical analysis of liquid metal corrosion, including species transport in solid steels, in flowing liquid metals, and mass exchange at liquid/solid interface. The survey illustrates the mechanisms of the liquid metal corrosion and sets up a system to calculate the corrosion rate and to study the corrosion species distributions in the solid and liquid metal/alloys. Both light liquid metal/alloy (sodium and sodium-potassium) and heavy liquid metal/alloy (liquid lead and lead-bismuth) are considered. Oxygen effects on liquid metal corrosion are also discussed. For liquid sodium and sodium-potassium the corrosion rate increases with increasing oxygen concentration, while for liquid lead and lead-bismuth it is reasonable to produce a protective oxide layer using an oxygen control technique which can mitigate the corrosion rate significantly. Finally, the corrosion-oxidation interaction in liquid lead and lead-bismuth are discussed.     

Electrochemical oxygen sensors for on-line monitoring in lead-bismuth alloys: status of development

This paper presents the state of development of oxygen sensors based on the electromotive force (emf) measurement at null current, using yttria stabilized zirconia as solid electrolyte for application in liquid lead-bismuth eutectic (LBE), which is envisaged as a nuclear coolant or as a spallation target in accelerator driven system (ADS) for nuclear waste transmutation. The assembly procedure, the calibration method, as well as the summary of the various validation tests undergone in both static and loop facilities are presented so as to define a real state of achievement and the basics needs for further studies. The sensors are efficient, accurate, rapid and reliable for research loops. However, the poor mechanical resistance as well as the effect of traces of impurities, promoting an increasing time-drift under certain conditions, are to be further studied to improve the sensor reliability for a nuclear use. The oxygen and chromium solubilities were reassessed in the process of the sensor testing, those relations are also given and discussed.     

Solid state transport as a mechanism of oxygen thermomigration in (U,Pu)O2±x

A general account is given of the theory of thermomigration as it applies to oxygen redistribution via the solid state in non-stoichiometric mixed uranium-plutonium oxide. This predicts that oxygen redistributes down the temperature gradient in hypostoichiometric material and up in hyperstoichiometric material. Some previous treatments are criticised. The evidence from laboratory experiments suggests that solid state transport is the dominant mechanism. A treatment, such as the cluster model, based on the manner in which oxygen deficiency or excess is accommodated in the structure, accounts naturally for the observed behaviour. The CO₂/CO route may be limited because of sluggish transfer of oxygen between the solid and the gas mixture. The H₂O/H₂ route could be important in reactor fuel pins during service, the behaviour then being different from that found in the out-of-pile work.     

Radiolytic hydrogen evolution in a closed vessel

Radiolytic hydrogen gas evolution under the liquid-gas two-phase condition has been studied using a closed vessel and γ -rays from a Co-60 source to develop an evaluation method for the H₂ evolution amount during transfer and storage of radioactive materials. An experiment was conducted using a closed vessel in which air and aerated pure water were present at room temperature. Several vessels were irradiated once with ?-rays at 5.2 × 10³ Gyh^–1. It was found that apparent G-values of H₂ production, calculated with a pressure increase of the closed vessel, became smaller for the cases of higher ratio of gas phase volume to liquid phase volume due to the recombination reaction of radiolytic H₂ with O₂ and H₂O₂. Also, equilibrium H₂ partial pressure became 10 times higher than the expected value using Henry’s law. These behaviours were explained by the developed model, which includes the liquid-gas distribution ratio of radiolytic H₂, the equation of state for H₂ in the gas phase, and the effective volume of liquid phase relevant to the liquid-gas distribution under the irradiation conditions. The effective volume of liquid phase was determined by considering the extent of the recombination reaction of radiolytic H₂ during mass transfer from the liquid phase to the gas phase.     

RELAP5铅铋快堆模型拓展及验证

为研究铅铋快堆瞬态热工水力特性,对RELAP5程序进行二次开发,添加铅铋合金（LBE）物性模型和液态金属流动换热模型,并与NACIE-UP和CIRCE-ICE台架的实验结果进行对比。计算结果表明：NACIE-UP台架稳态流量和温度相对误差在2%以内,瞬态相对误差不超过5%,与其他系统程序CATHARE、ATHLET、RELAP5-3D、RELAP5/MOD3.3(modified)相比,本文程序的相对偏差不超过10%;CIRCE-ICE台架稳态流量和温度相对误差在2%以内,瞬态相对误差不超过10%。本文程序满足反应堆系统热工水力分析程序精度要求,可作为铅铋快堆安全分析的有效工具。     

Hydrogen Isotope Separation by Plasma-Chemical Method

Deuterium transfer (exchange) reaction as shown in HDO+H₂=H₂O+HD was studied as a case similar to the tritium transfer reaction as shown in DTO+D₂=D₂O+DT, the first step in tritium isotope separation of the tritiated heavy water DTO. The transfer reaction was plasma-chemically catalyzed by allowing a gas mixture such as H₂O/D₂, D₂O/H₂, H₂O/HDO/H₂ or H₂O/D₂O/HDO/H₂ to flow through an atmospheric pressure discharge zone formed in a reaction chamber, the inner temperature of which was maintained just above 100°C. The plasma-chemical reactions diagnosed by infrared and emission spectroscopy revealed that the mixture underwent instantaneous deuterium transfer reactions as it passed the zone. The effectiveness of the method was demonstrated by high deuterium transfer rate, high separation factor of the transfer and a possibility of miniaturizing the separation facility.     

Blanket materials for fusion reactors: Comparisons of thermochemical performance

Thernodynamic calculations have been made to predict the thermochemical performance of the fusion reactor breeder materials, Li₂O, LiA10₂, and Li₄SiO₄ In the temperature range 900–1300 K and in the oxygen activity range 10^?25 to 10^?5. Except for a portion of these ranges, the performance of LiAlO₂ Is predicted to be better than that of Li₂O and Li₄SiO₄. The protium purge technique for enhancing tritium release is explored for the Li₂O system; it appears advantageous at higher temperatures but should be used cautiously at lower temperatures. Oxygen activity Is an Important variable in these systems and must be considered In executing and Interpreting measurements on rates of tritium release, the form of released tritium, diffusion of tritiated species and their Identities, retention of tritium in the condensed phase, and solubility of hydrogen isotope gases.     

European research on HLM thermal-hydraulics for ADS applications

The objective of the European 6th framework project EUROTRANS is to demonstrate the technical feasibility of transmutation of high level nuclear waste using accelerator driven systems. Within this objective the design of a European experimental ADS should demonstrate the technical feasibilities to transmute a sizeable amount of waste and to operate an ADS safely. This ADS will be a subcritical reactor system having liquid lead-bismuth eutectic as coolant. The liquid lead-bismuth eutectic is also intended to serve as target material for the spallation reaction which forms a crucial part to the subcritical reactor core. Since lead-bismuth eutectic is used as core coolant and spallation material, knowledge of its thermal hydraulic behaviour is essential. Within the DEMETRA domain of the EUROTRANS project, basic thermal hydraulic studies in order to support the design and safety analysis of XT-ADS components and the development of measurement techniques have been started.     

Active oxygen control by a PbO mass exchanger in the liquid lead–bismuth eutectic loop: MEXICO

Accurate control of dissolved oxygen concentration is crucial in order to use liquid lead alloys as a coolant of advanced nuclear systems. An oxygen control system based on PbO mass exchanger (PbO MX) technology was implemented in order to control the dissolved oxygen concentration in the liquid lead--bismuth eutectic (LBE) loop MEXICO. The oxygen control system consisted of a packed bed of PbO spheres, an oxygen sensor and a pneumatic control valve. The concentration of dissolved oxygen in the loop was controlled by regulating the LBE flow through the PbO MX using a proportional–integral–derivative (PID) controller with feedback from the oxygen sensor. Highly accurate control of the dissolved oxygen concentration in the loop was achieved by this system.     

Corrosion behaviour of stainless steels in flowing LBE at low and high oxygen concentration

The corrosion behaviours of austenitic steel AISI 316L and martensitic steel T91 were investigated in flowing lead-bismuth eutectic (LBE) at 400 °C. The tests were performed in the LECOR and CHEOPE III loops, which stood for the low oxygen concentration and high oxygen concentration in LBE, respectively. The results obtained shows that steels were affected by dissolution at the condition of low oxygen concentration (C_[O2] = 10⁻⁸-10⁻¹⁰ wt%) and were oxidized at the condition of high oxygen concentration (C_[O2] = 10⁻⁵-10⁻⁶ wt%). The oxide layers detected are able to protect the steels from dissolution in LBE. Under the test condition adopted, the austenitic steel behaved more resistant to corrosion induced by LBE than the martensitic steel.