Polonium formation in Pb-55.5Bi under proton irradiation

Lead-bismuth eutectic (LBE) has been proposed both as spallation target and as coolant in a future accelerator driven system (ADS). The safety analyses require knowledge concerning the elements formed during proton irradiation, and their volatility. Discs of lead-bismuth eutectic (LBE) were irradiated with protons having 71 and 590 MeV energy resp. to analyse Po-isotopes formation. The generation of the isotopes Po 206 and 208 was clearly indicated. The ratio ²⁰⁶Po/²⁰⁸Po is dependent on the proton energy and as well on the beam intensity. In parallel to the analytical examinations calculations were carried out using the FLUKA Monte Carlo code to compare the analytical results with the calculations. The evaporation behaviour of irradiated LBE discs was examined as well whereby volatile Hg was found, but no Po evaporation was detected under the chosen conditions.     

Overall mechanical properties of fiber-reinforced metal matrix composites for fusion applications

The high-temperature strength and creep properties are among the crucial criteria for the structural materials of plasma facing components (PFC) of fusion reactors, as they will be subjected to severe thermal stresses. The fiber-reinforced metal matrix composites are a potential heat sink material for the PFC application, since the combination of different material properties can lead to versatile performances. In this article, the overall mechanical properties of two model composites based on theoretical predictions are presented. The matrix materials considered were a precipitation hardened CuCrZr alloy and reduced activation martensitic steel `Eurofer'. Continuous SiC fibers were used for the reinforcement. The results demonstrate that yield stress, ultimate tensile strength, work hardening rate and creep resistance could be extensively improved by the fiber reinforcement up to fiber content of 40 vol.%. The influence of the residual stresses on the plastic behavior of the composites is also discussed.     

Bending tests on T91 steel in Pb-Bi eutectic, Bi and Pb-Li eutectic

The influence of specific liquid metals on the behaviour of the ferritic/martensitic steel T91 are investigated to understand better the processes taking place at the metal surface. Of special interest is particularly if there is a penetration of selected elements out of the melt along grain boundaries. Metallurgical investigation, SEM and EDX analyses analysis were performed on bent T91 specimens exposed to static LBE, Bi and Pb-17Li at 300 °C for 1000 h. Steel T91 was used in the standard and specially annealed conditions. It is shown that the heat treatment of the steel has a strong influence on the corrosion resistance. Additionally the strain affected on the component is responsible for the occurrence of LME.     

Corrosion behavior of Al-surface-treated steels in liquid Pb-Bi in a pot

Corrosion tests were performed in oxygen-saturated liquid Pb-Bi at 450 °C and 550 °C in a pot for 3000 h for Al-surface-treated steels containing various levels of Cr contents. The Al surface treatments were achieved using a gas diffusion method and a melt dipping method. Al₂O₃, FeAl₂ and AlCr₂ produced by the gas diffusion method exhibited corrosion resistance to liquid Pb-Bi, while the surface layer produced by the melt dipping method suffered a severe corrosion attack. Fe₄Al₁₃ and Fe₂Al₅ produced by the melt dipping method disappeared during the corrosion test at 550 °C and only FeAl remained.     

Corrosion behaviour of aluminized martensitic and austenitic steels in liquid Pb-Bi

The Pb-Bi liquid alloy is under consideration as a spallation target material in the hybrid systems due to its suitable nuclear and physical properties. In order to limit the risks of corrosion of the structural elements in contact with the liquid Pb-Bi, protection by means of aluminized coatings was investigated for 316L austenitic steel and T91 martensitic steel. For both steels, no damages were observed after immersions in static Pb-Bi up to 500 °C for low oxygen concentrations and long durations. However, at 600 °C in the same conditions, a non-uniform degradation of the coatings was observed. Only coated 316L was tested in dynamic conditions. The results were generally satisfying for temperatures from 350 to 600 °C and for fluid velocities up to 2.3 m s⁻¹. However, in both the IPPE loops and the CICLAD device, some localized damage of the coatings, attributed to erosion, was observed.     

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.     

Mechanical properties of martensitic steels after exposure to flowing liquid metals

This paper describes the tensile test results of martensitic steels EUROFER 97 and T91 after exposure to flowing Pb-17Li and Pb-55.5Bi alloy, respectively. The corrosion tests were performed in LIFUS II loop (Pb-17Li) and LECOR loop (Pb-55.5Bi) located in the ENEA Brasimone Center. Tensile test were carried in SYNTECH test machine under Ar atmosphere with an extension rate of 2 mm/min, and test temperature for EUROFER and T91 steels were at 480 and 400 °C respectively. The exposure of EUROFER steel to the liquid Pb-17Li did not affect its mechanical properties, while the ductility of T91 steel was deteriorated after exposed to flowing liquid Pb-55.5Bi.     

Mechanical behaviour of the T91 martensitic steel under monotonic and cyclic loadings in liquid metals

The paper deals with the mechanical properties in liquid metals of the T91 martensitic steel, a candidate material for the window of an accelerating driven system (ADS). Two main questions are examined, the risk of liquid metal embrittlement and the accelerated fatigue damage by a liquid metal. It is found that the transition from ductile to brittle behaviour induced by a liquid metal is possible as a result of a decrease in surface energy caused by the adsorbed liquid metal. The embrittlement can occur only with a hard microstructure and a nucleation of very sharp defects inside the liquid metal. Under cycling straining, the fatigue resistance of the standard T91 steel is decreased by a factor of about 2 in the liquid metal as compared to air. It is proposed that short crack growth is promoted by the liquid metal which weakens the microstructural grain boundary barriers and skip the microcrack coalescence stage.     

The impact of the composition of structural steels on their corrosion stability in liquid Pb-Bi at 500 and 400 °C with different oxygen concentrations

In recent years, heavy liquid metals have found exercise as possible coolants and targets in the conversion of radioactive elements in accelerator driven systems (ADS). Liquid lead-bismuth eutectic alloy is one of candidates for this using tanks to its suitable nuclear and physical properties. Performed examination was aimed at research of compatibility choice materials for parts of ADS with liquid Pb-Bi eutectic alloy, influence of composition choice materials on their corrosion resistance, influence of temperature and oxygen content. We performed corrosion tests of 1000 h each on approximately 20 types of structural steels (austenitic, ferritic and martensitic) in convection loops with flowing Pb-Bi at 500 and 400 °C and using different oxygen concentrations. The impact of Fe, Cr, Ni, Mn, Si, Al and Mo content on the corrosion stability of these steels was measured without and after preliminary passivation through creating thin spinel or oxide layers on their surface.     

Wetting of W by liquid Pb and PbLi alloys and surface interactions

Wetting of W by Pb and Pb–17 at.%Li in the range 400–900 °C is studied by the dispensed drop technique. Experiments are performed using different furnace atmospheres (high vacuum, reducing gas) and different heat treatments to achieve W deoxidation. A simple pairwise model is used to explain the relation between surface interaction, which is responsible for wetting, and bulk interactions determining miscibility.     

Temperature dependence of liquid Sn sputtering by low-energy He and D bombardment

Absolute sputtering yields of liquid tin from 240 to 420 °C due to irradiation by low-energy helium and deuterium have been measured. For ion energies ranging from 300 to 1000 eV, temperature enhancement of liquid tin sputtering was noted. These measurements were obtained by IIAX (the Ion-surface InterAction eXperiment) using a velocity-filtered ion beam at 45° incidence to sputter material from a liquid tin target onto deposition monitors. Sputtering yields from 500 eV ion bombardment at 45° incidence increase from 0.1 ± 0.03 and 0.019 ± 0.008 Sn particles/ion at room temperature, for He⁺ and D⁺ ions respectively, to 0.30 ± 0.12 and 0.125 ± 0.05 Sn particles/ion for 380 °C. Temperature enhanced sputtering has been seen in other liquid metals (namely lithium, tin-lithium, and gallium) using both ion beam and plasma irradiation.     

Behavior of steels in flowing liquid PbBi eutectic alloy at 420-600 °C after 4000-7200 h

This paper presents the results of steel exposure up to 7200 h in flowing LBE at elevated temperatures and is a follow-up paper of that with results of an exposure of up to 2000 h. The examined AISI 316 L, 1.4970 austenitic and MANET 10Cr martensitic steels are suitable as a structural material in LBE (liquid eutectic Pb₄₅Bi₅₅) up to 550 °C, if 10⁻⁶ wt% of oxygen is dissolved in the LBE. The martensitic steel develops a thick magnetite and spinel layer while the austenites have thin spinel surface layers at 420 °C and thick oxide scales like the martensitic steel at 550 °C. The oxide scales protect the steels from dissolution attack by LBE during the whole test period of 7200 h. Oxide scales that spall off are replaced by new protective ones. At 600 °C severe attack occurs already after 2000 and 4000 h of exposure. Steels with 8-15 wt% Al alloyed into the surface suffer no corrosion attack at all experimental temperatures and exposure times.     

An electrochemical hydrogen meter for measuring hydrogen in sodium using a ternary electrolyte mixture

An electrochemical sensor for measuring hydrogen concentration in liquid sodium that is based on a ternary mixture of LiCl, CaCl₂ and CaHCl as the electrolyte has been developed. DSC experiments showed the eutectic temperature of this ternary system to be ∼725 K. Impedance spectroscopic analysis of the electrolyte indicated ionic conduction through a molten phase at ∼725 K. Two electrochemical hydrogen sensors were constructed using the ternary electrolyte of composition 70 mol% LiCl:16 mol% CaHCl:14 mol% CaCl₂ and tested at 723 K in a mini sodium loop and at hydrogen levels of 60-250 ppb in sodium. The sensors show linear response in this concentration range and are capable of detecting a change of 10 ppb hydrogen in sodium over a background level of 60 ppb. Identification of this electrolyte system and its use in a sensor for measuring hydrogen in sodium are described in this paper.     

Critical temperature of the lead-bismuth eutectic (LBE) alloy

Liquid metals such as Bi and Pb and Pb-Bi eutectic alloy are serious contenders for use as coolant in LMFBRs in lieu of sodium due to a number of attractive characteristics (high density, low moderation, low neutron absorption and activation, high boiling point and poor interaction with water and air, etc.). Analysis of hypothetical accidents is of relevance to predict the catastrophe involving loss of coolant accident (LOCA) in LMFBRs. One key parameter to take into account is the critical temperature data of the liquid metals for reactor safety analysis. This communication reports the application of a theoretical model called internal pressure approach to predict the critical temperature (T_c) of the LBE alloy for the first time.     

Corrosion of stainless steels in lead-bismuth eutectic up to 600 °C

An experimental program has been carried out to understand the differences in the corrosion behaviour between different stainless steels: the austenitic steels 304L and 316L, the martensitic steels F82Hmod, T91 and EM10, and the low alloy steel P22. The influence of oxygen level in Pb-Bi, temperature and exposure time is studied. At 600 °C, the martensitic steels and the P22 steel exhibit thick oxide scales that grow with time, following a linear law for the wet environment and a parabolic law for the dry one. The austenitic stainless steels show a better corrosion behaviour, especially AISI 304L. Under reducing conditions, the steels exhibit dissolution, more severe for the austenitic stainless steels. At 450 °C, all the materials show an acceptable behaviour provided a sufficient oxygen level in the Pb-Bi. At reducing conditions, the martensitic steels and the P22 steel have a good corrosion resistance, while the austenitic steels exhibit already dissolution at the longer exposures.     

A review of refractory metal alloys and mechanically alloyed-oxide dispersion strengthened steels for space nuclear power systems

Mechanical and thermo-physical properties of refractory metal alloys and mechanically alloyed (MA)-oxide dispersion strengthened (ODS) steels are reviewed and their potential for use in space nuclear reactors is examined. Preferable refractory alloys for use in liquid metal and gas-cooled space reactors include Nb-1%Zr, PWC-11, Mo-TZM, Mo-xRe where x varies from 7% to 44.5%, T-111 and ASTAR-811C. These alloys are heavy, difficult to fabricate, and are not readily available. The advantages of the MA-ODS alloys are: (a) their strength at high temperatures (>1000 K), which decreases slower with temperature than those of niobium and molybdenum alloys; (b) relatively lightweight and less expensive; (c) low swelling and no embrittlement with exposure to high-energy neutrons (>0.1 MeV) up to 10²⁷ n/m²; and (d) high resistance to oxidation and nitration. The few data available on compatibility of MA-ODS alloys with alkali liquid metals up to 1100 K are encouraging, however, additional tests at typical temperatures (1000-1400 K) in space nuclear reactors are needed. The anisotropy of MA-ODS alloys when cold worked, and particularly rolled into tubes, should not hinder their use in space nuclear power systems, in which operation pressure is either near atmospheric or as high as 2 MPa, but joints weldability is an issue.     

Corrosion behaviors of US steels in flowing lead-bismuth eutectic (LBE)

Corrosion tests of several US martensitic and austenitic steels were performed in a forced circulation lead-bismuth eutectic non-isothermal loop at the Institute of Physics and Power Engineering (IPPE), Russia. Tube and rod specimens of austenitic steels 316/316L, D-9, and martensitic steels HT-9, T-410 were inserted in the loop. Experiments were carried out simultaneously at 460 °C and 550 °C for 1000, 2000 and 3000 h. The flow velocity at the test sections was 1.9 m/s and the oxygen concentration in LBE was in the range of 0.03-0.05 wppm. The results showed that at 460 °C, all the test steels have satisfactory corrosion resistance: a thin protective oxide layer formed on the steel surfaces and no observable dissolution of steel components occurred. At 550 °C, rod specimens suffered rather severe local liquid metal corrosion and slot corrosion; while tube specimens were subject to oxidation and formed double-layer oxide films that can be roughly described as a porous Fe₃O₄ outer layer over a chrome-rich spinel inner layer. Neglecting the mass transfer corrosion effects by the flowing LBE, calculations based on Wagner’s theory reproduce the experimental results on the oxide thickness, indicating that the oxide growth mechanism of steels in LBE is similar to that of steels in air/steam, with slight modification by dissolution and oxide dissociation at the liquid metal interface.     

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.     

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.     

The influence of proton irradiation on the corrosion of HT-9 during immersion in lead bismuth eutectic

The impedance properties of the oxide on the martensitic-ferritic steel HT-9 were characterized during proton irradiation at the LANSCE WNR facility. Prior to the irradiation experiment, samples were pre-oxidized in moist air resulting in an oxide scale that was on the order of 3 μm thick. Samples were then irradiated during immersion in 473 K lead-bismuth eutectic at a proton current of approximately 63 nA. To assess corrosion rate in real-time, a sinusoidal voltage perturbation was applied across the oxide surface as a function of frequency and the corresponding current response was measured. This method yielded values of oxide impedance which were used in conjunction with Wagner’s oxidation theory to calculate corrosion rate. In general, proton irradiation was associated with an increase in corrosion rate.