Material Performance in Lead and Lead–Bismuth Alloy

Material Performance in Lead and Lead–Bismuth Alloy$ K Kikuchi, Ibaraki University, Tokai, Ibaraki, Japan r 2016 Elsevier Inc. All rights reserved.

1 2 2.1 3 4 5 6 7 8 9 10 10.1 10.2 10.3 10.4 10.5 11 References

Recent Lead-Alloy Activity Utilization of LA The Conceptual Models of ADS and MYRRHA Ferritic/Martensitic Steels Surface Treatment to F/M and Austenitic Steels ODS Steel Austenitic Stainless Steels Precipitation Formation Weldment Wetting Miscellaneous Issues Related to Materials Performance Equipment Specification Thermal Parameters in Use Drive of Molten Lead Bismuth Electromagnetic Flow Meters Oxygen Concentration Environment Outlook

Abbreviations ADS Accelerator-driven nuclear transmutation system AFM Atomic force microscopy BEM Back scattered electron microscope CERN European Organization for Nuclear Research DBTT Ductile-to-brittle transition temperature EB Electron beam EDX Energy-dispersed X-ray analyzer FIB Focused Ion Beam F/M Ferritic–Martensitic steel GESA Gepulste Elektronenstrahlanlage GIF Generation IV International Forum ICP Inductive-coupled plasma atomic emission spectrometer

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1 2 2 4 8 9 9 11 13 13 13 13 14 14 15 15 15 16

LA Lead alloy LBE Lead–bismuth eutectics LFR Liquid-metal-cooled fast reactor LINAC Linear accelerator MA Minor actinides MEGAPIE MEGA-watt Pilot Experiment MYRRHA Multi-purpose hYbrid Research Reactor for High-tech Applications PSD Position sensitive detector TEM Transmission electron microscope TIG Tungsten inert gas WDX Wave-dispersed X-ray analyzer 3DAP Three-dimensional atom probe

Recent Lead-Alloy Activity

A brief justification for the utilization of lead or lead bismuth for use as a coolant in nuclear energy systems was described in 2001 by H. Sekimoto with the following highlights.1 When the possibility of the utilization of nuclear energy was discovered, it was expected to be a primary energy source in the future. Fast reactors can utilize the entire energy content of natural uranium. The selection of a coolant was an important item for designing fast reactors. The neutron slowing-down caused by the coolant should be minimized. This is first made possible by decreasing the average atomic density of the coolant in the reactor core, and second by employing a nuclide with a large mass number as the coolant, whose neutron moderating power is low. A liquid metal is considered as the best coolant for using the second method. Initially liquid mercury was employed but was not successful in both the USA and Russia. Since then, several liquid metals were considered, including lead alloys, and finally sodium was selected.

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Change History: March 2015. K. Kikuchi made amendments throughout the text; added new sections to extend the framework to materials science and engineering. The scope is widen including engineering issue. 8 Weldment, 9 Wetting, and 10 Miscellaneous issues related to materials performance. Abstract was added and reference list updated.

Reference Module in Materials Science and Materials Engineering

doi:10.1016/B978-0-12-803581-8.00749-9

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Material Performance in Lead and Lead–Bismuth Alloy

However, public concern about the safety of sodium has increased following sodium leakage incidents, such that the development and deployment of fast reactors on more than a prototype scale has not occurred. In the first ten years of the 21st century, the study of the utilization of lead-alloys (LA) including lead–bismuth eutectics (LBE) had been explored for application to nuclear waste transmutation systems and lead–bismuth cooled nuclear reactors. In the accelerator driven nuclear transmutation system (ADS), LBE is a candidate for both the subcritical-reactor coolant and the spallation neutron source target. In addition, the lead or lead bismuth cooled fast reactor (LFR) is one of the four reactor types investigated in Generation IV systems proposed by the Generation IV international Forum (GIF). A LBE cooled Long-Life Safety Simple Small Portable Proliferation-Resistant Reactor has also been proposed.2 As a result of the investigations on LA, comprehensive literature has been published. The Working Group on LBE of the OECD/ NEA Nuclear Science Committee3 published a handbook and review reports on LA technology. As part of the development of advanced nuclear systems, including ADS proposed for high-level radioactive waste transmutation and Generation IV reactors, heavy liquid metals such as lead or LBE were investigated as reactor core coolant and spallation targets. Heavy liquid metals were also being envisaged as target materials for high-power neutron spallation sources. The objective of the handbook is to collate and publish properties and experimental results on lead and LBE in a consistent format in order to provide designers with a single source of qualified properties and data and to guide subsequent development efforts. The handbook covers liquid lead and LBE properties, material compatibility and testing issues, key aspects of the thermal-hydraulic and system technologies, existing test facilities, open issues and perspectives. Zhang and Li4 reviewed the studies on fundamental issues in LBE corrosion. They included phase diagrams, thermodynamics, physical properties, corrosion mechanisms, oxygen control, experimental results, and corrosion results. Some recommendations were proposed for future studies: precipitation and deposition of corrosion products; oxygen transport; oxide formation and kinetics in lead alloys; coolant hydrodynamic effects; steel composition, microstructure and surface effects; and corrosion models. These are key areas for future research. Fazio et al.5 characterized corrosion property for Ferritic-Martensitic (F/M) steels and austenitic steels in stagnant LA based on results of corrosion tests. This report briefly summarized the current status on lead-alloy activities. At a temperature below 450 1C, adequate oxygen activities in the liquid metal steels form an oxide layer that behaves as a corrosion barrier. In the temperature range above 500 1C, corrosion protection because of the oxide scales seems to fail. A mixed corrosion mechanism has been observed, where both oxide scale formation and dissolution of the steel elements occurred. However, in this high temperature range, it has been demonstrated that coating the steel with FeAl alloys can enhance the corrosion resistance of structural materials. Experiments performed in flowing LA (mostly LBE) confirm that the corrosion mechanism of the steels depends on the oxygen content in LA. At relatively low oxygen concentration the corrosion mechanism changes from oxidation to dissolution of the steel elements. The experimental activity also extends up to temperatures of 750 1C for ODS alloys and their welded variants in Pb. The use of materials at higher temperatures will also require investigation of creep rupture. MEGAPIE was the MEGA-watt Pilot Experiment done at PSI in 2006 for developing a LBE spallation target. The MEGAPIE project was started as an essential step toward demonstrating the feasibility of coupling a high power accelerator, a spallation target, and a subcritical core assembly. The project was expected to furnish important results regarding safe treatment of components that had come into contact with lead–bismuth.6 The design data was obtained and the operational mode was confirmed.7 Corrosion rates were estimated experimentally at 400 C for a LBE flow rate of 1 m s
1, and 2.2 m s
1 where the oxygen content in the LBE was less than 10–7 wt%. No protective oxide layer was produced on the steel surface. This oxygen content has been considered representative of the MEGAPIE conditions, since no oxygen control and monitoring system is anticipated to be used in the target. The estimated corrosion rates, 40–86 mm year
1, indicate that in the given testing conditions, the corrosion resistance of the steel does not represent a critical issue; especially since LBE temperature is expected to be lower (320 1C). The goals of the experiment were fully accomplished8: four months of reliable and essentially uninterrupted operation (beam trips and short beam interruptions permitted) at a power level as high as the accelerator was able to deliver (about 0.75 MW), excellent performance of the target and the dedicated ancillary systems, the proof of functionality of advanced proton beam safety devices and, last but not least, a superb neutronic efficiency delivering about 80% more neutrons for the users compared to the previously operated leadcannelloni target. Verification of performance will be scheduled in the post-irradiation experiment.

2 2.1

Utilization of LA The Conceptual Models of ADS and MYRRHA

Recent activity on materials research and development in LA, especially LBE, aims at realizing ADS, MEGAPIE, LFR, and MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications).9,10 It is valuable to know each specific environment for material usage in design studies. The material temperature at contact with LBE is slightly less than 500 1C in the spallation reaction area and less than 550 1C in the fuel core area, respectively, in normal conditions. Figure 1 shows the ADS concept. A superconducting linear accelerator (LINAC) is connected with a subcritical fast reactor. A high-energy proton beam is injected into the core of the reactor. Spallation reactions produce a number of neutrons from the

Material Performance in Lead and Lead–Bismuth Alloy

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Figure 1 The conceptual model of ADS with beam window.

Figure 2 The conceptual model of subcritical reactor in MYRRHA by courtesy of Dr J Bosch.37

lead–bismuth nuclei, which are then used to transmute Minor Actinides (MA). The interface between the beam duct and lead bismuth is called the beam window. For one example, a tank type reactor with 800 MW thermal power and LBE-coolant and spallation target was proposed.11–13 The proton beam energy is set at 1.5 GeV. The beam current varies between 10 and 20 mA according to criticality swings. In the steady state condition, as the beam window material generates heat by spallation reactions, and is cooled by flowing LBE. A temperature difference is established between the LBE, the material in contact with the LBE, and the material on the other side of the window, with the temperatures in these three regions being 400, 450 and 500 1C, respectively. As the MA core cladding material is gamma heated and the fuel adds radiation heat, temperatures reach, for example, a maximum of 500, 550 and 600 1C. The maximum average velocity in the particular flow channel of LBE is 1.8 and 2.0 m s
1, at the window and in the MA core region respectively. Figure 2 shows the conceptual model of MYRRHA consisting of an inner vessel, guard vessel, cooling tubes, spallation loops, primary heat exchangers and so on, but without a beam window.15 In this system, a high-energy proton beam with energy of 600 MeV is injected directly into the free surface of the lead–bismuth in the subcritical reactor core. The MYRRHA project aims to serve as a basis for the European experimental ADS. In the first stage, the project focuses mainly on demonstrating the ADS concept, safety research of sub-critical systems, and on nuclear waste transmutation studies. Subsequently, MYRRHA will be used as a fast spectrum irradiation facility dedicated to research on structural materials, nuclear fuel, liquid metal technology and associated aspects on one hand and as a radioisotope production facility on the other hand. The system consists of a proton

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Material Performance in Lead and Lead–Bismuth Alloy

accelerator that supplies a 600 MeV  3–4 mA proton beam to a LBE spallation target, delivering the primary neutrons, that in turn couples to a LBE cooled sub-critical fast core. The structural materials for MYRRHA need to withstand temperatures ranging between 2001 and 550 1C (normal operating temperature between 300 and 450 1C) under high spallation neutron flux and contact with liquid LBE. It is clear that the candidate materials need to be able to fulfill challenging requirements such as high thermal conductivity, high heat resistance, low thermal expansion, low ductile-to-brittle transition temperature (DBTT) shift, sufficient strength at elevated temperatures with limited loss of ductility and toughness, low swelling rate, high creep resistance, and good corrosion resistance.14 Studies of LA for developing ADS are also reported from points of views of conceptual ideas16,17 and related facility.18 In the 1990s, in Europe, the concept of Energy Amplifier due to ADS is proposed by C. Rubbia et al. European Organization for Nuclear Research (CERN),56 without the condition whether or not the initial energy source is secured. Since the explosion of nuclear power stations in Fukushima, quest of disposal problem in the development of new technologies of high-level radioactive raw waste is closed up, accelerator-driven transmutation system, lead bismuth eutectics is to be used as coolant and spallation target material, has been attracting attention as one of them.

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Ferritic/Martensitic Steels

An approach for using materials such as ferritic/martensitic and austenitic stainless steels in LA is to keep an oxide layer on the surface of the base metal in contact with LA by controlling the oxygen concentration in the LA.19–21 Too little oxygen in LA will lead to dissolution of the protective iron oxide. Excess oxygen solution in the LA will lead to the production of lead oxide that could plug the cooling tubes. Theory employed an equilibrium condition of metal oxidation at high temperatures in the Ellingham diagram.67 They are the reaction of the formation of iron oxide, 3Fe þ 4 O2Fe3O4, and the formation of lead oxide, Pb þ O2PbO. The Gibbs free energy values indicate lower and upper limits of oxygen concentration dissolved in the LBE, 0:5DG3 Fe3 O4 o RT ln (Po2)o2DG1 PbO, where PO2 : pressure of oxygen, DG1: Gibbs free energy, R: gas constant, T: absolute temperature. If oxygen concentration in LBE ranges between the lower and the upper limits, the steel used in LBE will form an oxide layer without a fear of channel closing due to lead oxide formation. Predicted concentration of dissolved oxygen in LBE exists between, for example, 10–6 and 10–4 mass% in the temperature range of 400 to over 500 1C.19 An alternative approach is to add anti-corrosion elements, like Al, to the surface, which leads to a protective oxide that guard base metals as mentioned in the section on surface treatment. The oxide scale is not a simple structure but consists of duplex layers; magnetite Fe3O4 near the LA side and spinel (FeCr)3O4 near the base metal. The original surface exits at the interface between the magnetite and spinel, but not at the front surface of the magnetite near the LA. An early question was how the oxide layers on the surface of the base metal grew. Martinelli et al.22–24 reported a global study on the oxidation process of Fe–9Cr–1Mo martensitic steel (T91) in static LBE. The isotope tracer oxygen-18 was employed in the corrosion test. Also, the mass balance of Fe and Cr was investigated theoretically. They explained the Fe–Cr spinel growth rate mechanism as follows: The oxidation reaction can occur because of the presence of nano-channel. Nano-channel formation is achieved by the dissociative/perforative growth in the magnetite. Nano-channel allows a fast diffusion of oxygen to the T91/spinel interface. Oxygen cannot diffuse in the oxide lattice because its rate is insufficient for Fe–Cr spinel formation, but instead is transported via short cut diffusion paths. Even if oxygen diffusion in grain boundaries could be possible, oxygen would likely diffuse inside nano-channels. The nano-channels are in some cases called lead nano-channel because of the results of the LBE oxidation tests. Liquid metal does not penetrate evenly in the oxide scales: only lead penetrations are observed. Nevertheless, in pure bismuth oxidation tests, bismuth penetrations are also observed into the scales. On the other hand, the iron diffusion from T91 to the magnetite/Pb–Bi interface leads to vacancy formation at the T91/Fe–Cr spinel interface. Because of the presence of chromium atoms, these vacancies can accumulate to form nano-cavities at the T91/Fe–Cr spinel interface. This accumulation is quasi complete; very few cavities are annihilated on the T91/oxide interface. The Fe–Cr spinel grows inside the nano-cavity until it is completely filled. At that moment the oxygen can no longer reach the T91 alloy and the oxidation reaction interrupts itself. The formed Fe–Cr spinel thickness then becomes equal to the consumed T91 thickness, because of this self-regulation process. In this process, the limiting step of the Fe–Cr spinel growth rate is thus the ‘iron diffusion’ across the oxide scale. Kikuchi et al.68 reported a study on corrosion layer formed on the HCM12A using three-dimensional atom probe (3DAP). It can analyze chemical composition at the atomic scale and make 3D imaging by handling over million data. The sample is prepared in the form of apex. The cooled apex is biased at high electric voltage. The very small radius of the apex, processed by focused ion beam, and the high voltage induce a very high static electric field at the apex surface. Under laser pulsing a few atoms are evaporated from the surface by ionization, and projected onto a position sensitive detector (PSD) with very high detection efficiency. The detector measures the time between the laser flash, the arrival time on the PSD, and the mass to charge state ratio. The position of the ion impact on the PSD allows reconstructing the original position of the atoms on the apex. The capability of oxide scale is to know distribution of each of element in the particular space, as the number of detected atom counts as well as atomic concentration. HCM12A materials, which formed duplex oxide layer in the flowing LBE was analyzed by 3DAP techniques.

Material Performance in Lead and Lead–Bismuth Alloy

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Figure 3 Atomic scale profile of Fe, Cr, and O with other minor element of Si in the spinel oxide of HCM12A near the magnetite and spinel boundary.

Figure 3(a) shows the retrieved apex sample, using FIB that includes both magnetite and spinel layer. Analyzed area is 500–700 nm away from the boundary of Fe–Cr spinel and magnetite layer. Spinel mages shown by the SEM X-ray analysis looks homogeneous microstructure. But a reality is inhomogeneous structure was disclosed from point of views of atomic scale. Cr super enrichment was detected and at the size of 4.5  25 nm and Si also enriched surrounding Cr enriched region as shown in Figure 3(b). A key issue in maintaining structural integrity is to maintain high performance of the welded materials. The corrosion properties between the base metal and the weldment were investigated.25 The materials tested were F/M steel F82H26 and the electron beam (EB) welding of F82H. The chemical composition of F82H is 8Cr–2W–0.2VTa–bal/Fe (wt%). Oxygen concentration was controlled to (2–4)  10–5 mass%. Welded materials were prepared with a bead-on-plate weldment with a 15 mm depth of melting. F82H steel was welded after preheating at 300 1C, heat-treated at 300 1C for 2 h, and then annealed at 750 1C for 2 h for stress relief. Figure 4 shows optical microscope observation of cross-section for F82H specimens and an impinging-flow simulation around the specimen. It was observed that the welded metal of F82H revealed a coarse martensitic structure in comparison with the fine microstructure in the non-welded region because of melting and re-solidification in the welding process. The corrosion depth in F82H was limited near the surface of the material. A failure of the outside layer in the duplex corrosion layers was observed. The heat-affected zone showed that the martensitic structure became fine because of the rapid heating and cooling during the welding process. Regardless of the difference in microstructures, the corrosion layer showed no apparent difference. The growth of the corrosion depth, defined by the layers of magnetite and spinel, followed a parabolic law, where diffusion controls the process. The result of the flow simulation of LBE impingement indicated that the velocity varied from 0 to 1 ms
1 near the specimen surface. At higher temperatures, for example, above 500 1C, the internal oxide layer or diffusion zone was clearly identified. Furukawa et al.27 observed three layers, consisting of the duplex layers mentioned earlier and a diffusion zone in the base metal beneath the spinel layer in the static LBE test at 500 and 550 1C under the oxygen controlto10–6 wt% for high Cr steel (10.54Cr–1.75W–MnMoV) with heat treatment: 1070 1C, 100 min air-cooled; 770 1C, 440 min air-cooled.

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Material Performance in Lead and Lead–Bismuth Alloy

Figure 4 Optical microscope observation of cross section for F82H specimens and an impinging-flow simulation around the specimen. (a) Macro structure including welded zone and heat affected zone, (c) micro structure of welded zone tested at 450 1C for 1000 h, (d) micro structure of tip region tested at 450 1C for 1000 h, (e) cross section of tip region tested at 450 1C for 3000 h, (f) cross section of tip region tested at 500 1C for 1000 h, and (g) simulated flow profile of LBE around the specimen.

Tan and Allen tested high Cr steel material in the DELTA loop, at Los Alamos National Laboratory (LANL). The material tested was HCM12A, procured from Sumitomo Metal Industries, Ltd. with composition provided by the supplier: 10.83Cr–1.89W– 1.02Cu–0.64Mn–0.39Ni–0.30Mo–0.27Si–0.19V–0.11C–0.063N–0.054Nb–0.016P–0.002S–0.001Al–3.1  10–5B, and balance/Fe (wt%).28 The chemical composition and heat treatment of this material is slightly different from that used in the experiment by

Material Performance in Lead and Lead–Bismuth Alloy

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Furukawa and Muller. HCM12A is one of the third generation 12Cr ferritic steels with tempered martensite,29 which was originally developed for heavy section components such as headers and steam pipes for use at temperatures up to 620 1C and pressures up to 34 MPa30 with good resistance to thermal shocks.31 The HCM12A was received after being annealed at 1050 1C and tempered at 770 1C.28 They compared the oxide layer to the porous magnetite layer on the supercritical water exposed sample at 600 1C, 667 h. Temperatures at both conditions were different. It was found that detachment of most of the magnetite non-protective layer occurred on the LBE exposed sample at 530 1C – 600 h earlier in time than models developed by Zhang and Li. From a technical experimental point of view, it is the issue how to detect the original surface of base metal in order to evaluate the oxide thickness. A thin yttrium coating will help to detect it in the LBE corrosion test. According to Muller, there is the boundary of magnetite and spinel.57 Additionally, Schroer took into account the growth mechanism of the oxide film, the front of the base material is in the place where it went into the slightly magnetite side.58 The accompanying metal recession was assessed by a metallographic method and relevant kinetic laws. Conventionally, spinel structure of the oxide film cross-section are distinguished by X-ray analysis of Cr. Magnetite that does not contain Cr. Exactly crystal structure analysis is needed to prove it. With a scanning microscope surface potential mode measurement, SPM-9600 Shimadzu, of oxide film formed in the molten lead bismuth on the HCM12A, the drop of the surface potential at the boundary of these bands is detected and its value was shown 0.02 V and the boundary space was approximately 1.2 mm.59 Here surface potential measurement is equivalent with KFM, Kelvin Force Microscopy. Furukawa reported that at temperatures above 600 1C, the oxide layer grew thinner with increasing temperature, which suggests that around this temperature, a change occurred in the mechanism of oxidation. At 570 1C, FeO-wustite is formed. Compared with magnetite, wustite has a lower standard free energy of formation, which ensures its stable existence at low oxygen potential. In fact, the layer was formed in the region between magnetite and base metal. Also in this temperature range that is beyond the point of oxidation mechanism change, dissolution attack was observed at several points, and the number of such points increased with prolongation of run duration. The observations would suggest lowering the maximum processing temperature in LBE applications from point of view of the static LBE test.27 Hosemann et al. attempted nano-scale characterization of HT-9 (11.95Cr–1Mo–0.6Mn–0.57Ni–0.5W–0.4Si–0.33V–bal/Fe wt%) by using atomic force microscopy (AFM), using a function of magnetic force microscopy (MFM) and C-AFM. C-AFM is a contact mode electrical characterization technique that involves applying a voltage, typically, between the conductive AFM tip and the sample, while monitoring variations in the local electrical properties in a range of pA to mA. The HT-9 tube was tested at 550 1C in flowing LBE under 10–6 wt% oxygen for 3000 h.32 It was found that the oxide consists of at least four different layers with different grain structures and therefore conductivity/magnetic properties. The outer layers seem to be Fe3O4 and have good conductivity, while the inner layer is Cr enriched and has lower conductivity or is insulating. This is in agreement with the literature where Cr additions lower the conductivity of Fe3O4. The outer layer can be divided into two distinct areas based on a change in grain structure. The inner oxide layers adopt the grain structure from the bulk steel. High pore density within these layers suggests that these are fast diffusion paths allowing Fe diffusion outward and O diffusion inward. The LBE corrosion experiment in the DELTA Loop on T91, HT-9 and EP823 conducted for 600 h at 535 1C showed multi-layer oxides on the tested materials. The wave-dispersed X-ray analyzer (WDX) measurements on the cross sections revealed two Cr and Fe containing oxide layers and no Fe3O4 layer. It appears that the main difference between observed oxide layers is the Fe content and the microstructure. Nano-indentation tests across the oxide layers were performed.33 The results showed lower values of E-modulus in these oxide layers than the bulk steel layers and higher hardness values for the oxides than the bulk steel. The inner oxide layer is softer than the outer oxide layer. This might be due to the fact that the inner oxide layer has higher porosity than the outer layer. Yamaki and Kikuchi34 conducted a mechanical test of oxide scales. The beam window at the boundary of the high-energy proton beam and reactor core as shown in Figure 1, is loaded by thermal stress and buckling load in the deep LBE of the reactor.35 The specimen was a ring made from the F/M steel pipe, HCM12A. The inner surface of the pipe had been exposed to flowing LBE during the loop operation at 400–500 1C for 5500 h under an oxygen concentration in the range from 1  10–5 to 5  10–5 wt%. Apparently, the oxide layer had a duplex structure. Possibly they were outside magnetite and inner side spinel. Figure 5 shows the results of the ring compression test. The HCM12A ring was compressed by 50% and unloaded. Near the position A, cracking occurred due to an excess strain to the spinel layer rather than the Fe3O4 layer. This was caused by the fact that the Young's modulus of Fe–Cr spinel layer was lower than that of Fe3O4 layer by 10% with the same hardness in both layers. Near the position E the oxide layer was spalled off from the boundary between the base metal and spinel. Furthermore, testing of the mechanical strength of the oxide film itself was done using the same material with the abovementioned HCM12A. A 15 mm thick oxide layer was formed on the steels surface and micro bend bars were manufactured using a Focused Ion Beam (FIB) instrument perpendicular to the oxide layer. The cut bend bars were tested utilizing a Micro Materials nano-indenter at room temperature using a Berkovich indenter. It can be seen that the bend bar fractured brittle at the metal-oxide interface, no plastic deformation on the fracture surface, and the fracture stress evaluated to be 856 MPa.60 Furthermore Raman spectra analyses showed a Fe3O4 outer layer and a Cr-rich spinel structure inner layer.70 F/M steels can guard the base metal by forming spinel oxide layer. The iron diffusion rating controls the formation mechanism. The magnetite oxide layer, which is often formed in the outer side contacted, is not protected against contact with LBE. Under the tensile stresses, excess strains will spall off the oxide layer from the interface between the base metal and the spinel layer. Over 570 1C the oxide formation mechanism is changed by the formation of wustite.

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Material Performance in Lead and Lead–Bismuth Alloy

Figure 5 The ring compression test. (a) HCM12A ring model before compression, (b) the ring model after compression by 50%, (c) the ring after unloading, (d) simulation of maximum principal strain distribution induced at loading, (e) the cross section near position A, and (f) the cross section near position E.

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Surface Treatment to F/M and Austenitic Steels

Müller et al. demonstrated the effect of Al-alloying into the surface of the base metal was the F/M steel OPTIFER IVc (10Cr– 0.58Mn–0.56C–0.40W–0.28V–bal/Fe wt%) using electron pulse treatment, GESA (Gepulste Elektronenstrahlanlage).36,37 There was no corrosion attack visible in any part of the alloyed portion after 1500 h exposure to liquid lead at 550 1C with 8  10–6 atomic % oxygen. The alumina layer that must have formed at the surface during oxidation in lead might be very thin and could not be detected. Only the unalloyed part of the surface was covered with thick oxide scales. The results also suggested that the Fe–Cr spinel layer ends at the original specimen surface. This surface treatment had a similar result when applied to an austenitic steel base metal 1.4970(16.5Cr–13.8Ni–1.91Mn–0.81Si–MoTi–bal/Fe (wt%)). Weisenburger et al. examined T91 tubes with modified FeCrAlY coatings in LBE. These coatings are often used for turbine blade protection.38 The coating had an average thickness of 30 mm after application by a plasma spray method and was re-melted using the pulsed large area GESA EB to gain a dense coating layer and to improve the bonding between the coating and the bulk material. They intended to simulate a cladding material’s environment by using a pressurized tube type specimen. The results showed that the tangential wall stress of about 112.5 MPa induced by an internal tube pressure of 15 MPa increased the Fe diffusion and led to enhanced magnetite scale growth. Coated specimens, however, have no magnetite layer. This is another advantage of the coating. Energy-dispersed X-ray analyzer (EDX) line scans of the cross section of the coated T91 tube specimen after 2000 h exposure to LBE at 600 1C show that the top oxide scale must consist mainly of alumina followed by a thin layer enriched in Cr. These layers protect the steel not only from LBE attack but also from oxygen diffusion into the coating and bulk material. The coating process needs some improvement to avoid coating regions with aluminum concentrations below 4 wt%; otherwise the oxide layer will grow in the same manner as the original material. Steels with 8–15 wt% Al alloyed into the surface suffer no corrosion attack for all experimental temperatures and exposure times.39 Technical concerns about surface treatment are the effect of cyclic loading on the low cycle fatigue endurance in air and LBE. Low cycle fatigue tests were conducted in LBE containing 10–6 wt% dissolved oxygen with T91 steel at 550 1C. T91 was employed in two modifications, one in the as-received state, and the other after alloying FeCrAlY into the surface by pulsed EB treatment (GESA process). Tests were carried out with symmetrical cycling (R ¼ 1) with a frequency of 0.5 Hz and a total elongation Det/2 between 0.3% and 2%. No fatigue effects from

Material Performance in Lead and Lead–Bismuth Alloy

9

LBE could be detected. Results in air and LBE showed similar behavior. Additionally, no difference was observed between surface treated and non-treated T91 specimens.14 A melting process of coating materials enhances bonding between the coating and the bulk materials. Heat deposition due to a pulsed electron beam exposure successfully demonstrated that remelted alumina or FeCrAlY coating was effective to protect the base metal property from LBE attack. Surface coating of material protects the base material. It is a very powerful method of preventing corrosion in the particular period. On the other hand, preservation of coating function requires for in-service inspection. Damaging patterns are separation from the base metal, cracking and intrusion of flowing LA and mass loss due to erosion effect.

5

ODS Steel

Takaya et al.40 investigated the corrosion resistance of ODS steels with 0–3.5 wt% Al and 13.7–17.3 wt% Cr, at 550 and 650 1C for up to 3000 h in stagnant LBE containing 10–6 and 10–8 wt% oxygen. The ODS steels were manufactured by hot extrusion of mechanically alloyed powders at 1150 1C, and consolidated bars were annealed by 60 min of heat treatment at 1150 1C, followed by air cooling. Chemical compositions of ODS materials are (13.7–17.3) Cr–(1.9–3.5) Al–(0.34–0.36) Y2O3–TiSiMn–bal/Fe wt%. Protective Al oxide scales formed on the surfaces of the ODS steels with 3.5 wt% Al and 14–17 wt% Cr, and no dissolution attack was seen in any of the cases. Addition of Al is very effective in improving the corrosion resistance of ODS steels in LBE. On the other hand, the ODS steel with 16 wt% Cr and no Al showed no corrosion resistance except in the case of exposure to LBE with 10–6 wt% oxygen at 650 1C. Thus, the corrosion resistance of ODS steels in LBE may not be improved by solely increasing Cr concentration. There is additional data reported by Hosemann et al. on ODS alloys in LBE. Specimens were exposed to flowing LBE in the DELTA Loop at LANL at 535 1C for 200 h and 600 h. The oxygen content in the LBE was about 10–6 wt%. The detailed manufacturing process was not disclosed. Conclusively, PM2000, which has a chemical composition of 20Cr–5.5Al–0.5Y2O3–0.5Ti– bal/Fe (wt%), showed a very dense, thin and protective oxide layer due to its higher Al content. The compositions of the oxide layers found on the Al alloyed materials change with depth. Elements are oxidized based on the amount of oxygen available for oxidation and the free energy of the oxide. It appears that at least 5.5 wt% Al in the alloy is necessary in order to form a protective Al enriched oxide.41 The oxide scale has duplex structure below 500 1C. Over 500 1C a diffusion zone in the base metal is apparently observed. The oxide layer appears to consist of three layers, that is, the duplex layers plus the diffusion zones. The oxide scale does become unstable. The outer magnetite layer is prone to be spalled off in the flowing LA. In such an environment, the Al coating is found to be effective in enhancing corrosion resistance. Re-melting processes, for example, by GESA electron beam exposure, makes a good Al layer. The disadvantage of the coating method is the disintegration or cracking due to an uncontrolled process. This cracking could be attributed to the local reduction of Al content. The ODS alloy is developed for cladding materials. Materials development is progressing in the direction of high-Cr Al-ODS alloys. The recommended Al composition in ODS alloys varied from 3.5 to 5.5. An adequate amount of Al will balance the corrosion resistance and mechanical strength. Excess Al will reduce mechanical strength. Understanding why the Al enrichment in Fe-base steel improves corrosion resistance in LA will be determined in future investigations. Oxide dispersion-strengthened steel aims at enhancing the strength of material applicable to the cladding materials of fast reactor. The addition of Al to ODS improves corrosion resistance in LBE at the fuel cladding temperatures. On the other hand, the excess addition of aluminum reduces the strength of materials. An optimization is needed to balance the two factors at around 5%.

6

Austenitic Stainless Steels

Austenitic stainless steels are candidate materials for the spallation target window in ADS. In MEGAPIE, however, F/M steel, T91, was used for the beam window in flowing LA and this was acceptable for limited time duration (4 months). The lifetime of the beam window of the T91 liquid Pb–Bi container in the MEGAPIE target was summarized based on the present knowledge of LBE corrosion, embrittlement and radiation effects in the relevant condition.42 It was suggested that the lower bound of the lifetime of the T91 beam window was determined when the steel became brittle at the lowest operation temperature, 230 1C, with a safety margin of 30%. Evaluation using the DBTT data and fracture toughness values of T91 specimens tested in LBE, a dose limit of about 6 dpa, corresponding to 2.4 Ah proton charge to be received by the target in about 20 weeks in the normal operation condition was set. In the ADS design, for example, the beam window material will produce about 1000 appm (3He þ 4He) a year by 1.5 GeV proton beam bombardment in the reactor core for austenitic stainless steel, Japanese Primary Candidate Alloy (JPCA), and F/M steel, F82H.43 The helium production of 1000 appm He suggests that the ductile-to-brittle transition temperature (DBTT) will increase by 400–500 1C.44 This increase set the design temperature at the beam window to be 450–500 1C. The use of a F/M steel may lead to a brittle fracture and those materials should be avoided in operations for extended times. Therefore, austenitic steel will be the candidate material. The production of hydrogen and helium in JPCA was slightly larger, 3 to 4%, than that of F82H because of the addition of nickel and boron. JPCA, in which chemical composition is 0.50Si–1.77Mn–0.027P–0.005S–15.60Ni–14.

10

Material Performance in Lead and Lead–Bismuth Alloy

22Cr–2.28Mo–0.24Ti–0.0031B–0.0039N–bal/Fe (wt%), was developed in order to reduce the helium embrittlement of austenitic steel for first wall and blanket structural components in fusion reactors.45 The optimized JPCA material is manufactured by vacuum induction melting, vacuum arc melting and solution-annealing at 1100 1C during 1 h. The TiC precipitates within the matrix and on the grain boundaries, serve as trapping centers for the helium produced during neutron irradiation. However, dissolution of the MC precipitates initiated the onset of helium embrittlement as well as high swelling during high fluence neutron irradiation. The improved stability of MC precipitates, which formed in the matrix during irradiation, prevents loss of ductility at 500 1C and below. The corrosion properties of an austenitic stainless steel at low temperature demonstrated good endurance for material usage in LBE during a short time, approximately at 300 and 470 1C for 3000 h for 1.4970 austenitic stainless steel,46 and at 420 1C for 2000 h for 1.497 0 austenitic stainless steel and 316 L at an oxygen concentration of 10–6 wt%.47 No dissolution was seen in the above results. A thin oxide scale may protect the material from attack in LBE. As demonstrated in Figure 4, a corrosion test under impinging flow was also conducted on JPCA and its electron beam (EB) welded bar at an oxygen concentration of 2–4x10–5 wt%.48 The EB welded metal of JPCA exhibited a dendritic structure 1 mm in width but a heat-affected zone was not visible. SEM observation showed no corrosion layer for the specimens tested at 450 1C and 1000 h. But at 3000 h a thin corrosion layer could be observed at 1–2 mm in depth. For the weld joint, the depth of corrosion layer as well as corrosion morphology showed the same results as with the parent material. The results of X-ray diffraction analyses showed how the oxide layer developed at 450 and 500 1C. Figure 6 shows X-ray diffraction analyses of the JPCA specimens under the conditions of 1000 h at 450 1C (top, JPCA-1), 1000 h at 500 1C (middle, JPCA-2) and 3000 h at 450 1C (bottom, JPCA-3). Oxidation of the JPCA at 450 1C progressed at the same manner as at 500 1C. There is an attempt of cold working to austenitic steel. Expected advantage is the change of the apparent increase of elastic strength and the material microstructural transformation. As austenitic steel is soft as compared to the F/M steel, erosion was observed in the BL-1 lead bismuth loop with heavy LBE flow at JAEA,49,61 and also reported in the LINCE lead bismuth loop at CIEMAT.63 The effect of 20% cold working on the compatibility of JPCA in flowing Pb–Bi eutectic at 450 1C from a corrosion behavior viewpoint was also done in the same flowing loop. The temperature was set as the practical operating condition of the proton beam window in the ADS design. Rivai et al. analyzed the tested JPCA.62 Pb–Bi penetrates into the matrix through the ultra narrow-channels within the ferrite layer and accumulates beneath the layer. On the contrary, no ferrite layer forms in 20% coldworked JPCA. Twenty-percent cold working limits the dissolution attack of Pb–Bi. The iron-chromium oxide layer, which forms from the a0 martensitic structure protects the surface from dissolution attack by Pb–Bi. However, localized superficial pitting corrosion occurs because of low oxygen concentration conditions and structural defects. For JPCA without cold working, ferritization occurs because of Ni and Cr dissolution into the Pb–Bi, resulting in the formation of a thin ferrite layer.48,49,51 A change to metallurgical characteristics of JPCA is induced by the twenty-percent cold working, and influence the corrosion behavior of the material in flowing Pb–Bi at 450 1C. Twenty-percent cold working causes slip or dislocation within crystals and therefore causes plastic deformation. Slip or dislocation and plastic deformation induce structural transformation of the JPCA from an austenitic structure (g, FCC, non-magnetic) into a martensitic structure (a0 , BCC, magnetic). Figures 7(a) and 7(b) shows the MFM analyses for the JPCA without cold working and the 20% cold-worked JPCA, respectively. In the MFM analyses, magnetic polarization is indicated by the strong dark color. The figures show clearly the magnetic polarization differences between the samples. Figure 7(b) reveals the existence of magnetic polarization bands in the 20% cold-worked JPCA structure bands, which do not exist in the JPCA, as shown in Figure 7(a). Non-magnetic structure is one of the characteristics of

Figure 6 X-ray diffraction analyses of JPCA specimens under the condition of 1000 h at 450 1C (top, JPCA-1), 1000 h at 500 1C (middle, JPCA2) and 3000 h at 450 1C (bottom, JPCA-3).

Material Performance in Lead and Lead–Bismuth Alloy

11

Figure 7 AFM-MFM observation of cross section for tested materials. (a) JPCA SS without cold working, and (b) 20% cold-worked JPCA SS.

austenitic stainless steel. The results show that the 20% cold working has transformed the structure of the non-magnetic austenite into a magnetic structure.62 Corrosion test results for austenitic stainless steels have been reported in LBE. The oxide layer formed on the steel is very thin at 400–450 1C, compared with F/M steels. Nickel dissolution from the base metal to flowing Pb–Bi causes ferritization. Twenty percent of cold working showed less ferritization and changed austenitic structure to martensitic one; those change corrosion properties in LBE. In ADS the beam window, which will be bombarded high-energy proton particle, has an issue of spallation irradiation damage. Austenitic stainless steels are free from DBTT issue.

7

Precipitation Formation

The dissolution of Ni, Cr, and Fe from structural materials into LA was studied. Saturated solubility of Ni in LA is calculated to be a couple of wt% at 450–500 1C.20 Corrosion–erosion tests have been conducted at the JLBL-1 facility of the JAEA. The main circulating loop was made of SS316 austenitic stainless steel, and consisted of the specimens at high temperature and low temperature, filters, a surge tank, a cooler, an electro-magnetic flow meter, a surface-level meter, thermocouples, and a drain tank.49 The loop was operated at a maximum temperature of 450 1C with a temperature difference estimated to be 10–7 wt%, according to measurements using an oxygen probe. The testing specimen tube is a cold-drawn seamless type SS316, which was produced as a tubing form with 13.8 mm outer diameter, 2 mm thickness and 40 cm length. The tube was solution-heat treated at 1080 1C for 1.5 min and then cooled rapidly. Figure 8 shows both the EDX analyses of the low-temperature specimen after corrosion–erosion testing for the 3000 h and the SEM image of an unused specimen. The surface of unused specimen was

12

Material Performance in Lead and Lead–Bismuth Alloy

characterized by the creviced structure. This feature resulted from the acid washing in the manufacturing process during the material preparation. It was found that precipitated materials existed with the solidified LBE on the tube. The precipitation consists mainly of Fe and Cr as measured using energy dispersive X-ray analyses and apparently looks crystalline. The quantitative analyses by means of a focused-ion beam, X-rays and Transmission Electron Microscope (TEM) showed that the weight concentration ratio was roughly Fe:Cr ¼ 9:1, for example. Nickel was not found in the crystals or in the solidified LBE. The precipitations occur in the lead–bismuth including impurities dissolved from SS316 at the high temperature portion of the test. Zhang and Li4,50 calculated the corrosion/precipitation rate for iron using a kinetic corrosion model and the temperature profile for the JLBL-1 loop. They reported that the observed deposition zones in the JLBL-1 loop could be exactly predicted using the nonisothermal and multi-modular corrosion model. The predicted corrosion rate is about 0.05–0.08 mm per 3000 h if the diffusion coefficient is selected as 3.9  10–9 m2 s
1. This agrees well with the experimental results of 0.03–0.1 mm. Ni-rich precipitation was found in the JLBL-1 loop after a total operation time of 9000 h was achieved. Figure 9 shows Ni-rich precipitation in an SEM (low magnification) and laser Microscope (high magnification) images on the surface of solidified LBE.51 The solubility of Ni is higher than that of Fe and Cr, around a couple of wt% in the temperature range of 350 to 450 1C. For the measurement of Ni in LBE, an Inductive Coupled Plasma atomic emission spectrometer (ICP, ULTIMA2) was used for analyses. It was found that the Ni concentration was below 0.1 wt%. In addition, Ni-rich precipitates were found not only at the high temperature part but also at the low temperature part, and on the surface of residual LBE. This was not the case for Fe–Cr precipitates. Fe–Cr precipitates were only found at the low temperature part. The driving force for Fe–Cr precipitates was concluded to be a difference of the saturation concentration at different temperatures. It can be assumed that the Ni-rich precipitates formed on the surface of the residual LBE during a cooling period, although the precipitation rate is not known for the establishment of such a Ni-rich structure.

Figure 8 EDX analyses of low-temperature specimen after corrosion-erosion test at JLBL-1 and SEM image of unused specimen.

Figure 9 Ni-rich precipitates of SEM (low mag.) and Laser Microscope (high mag.) on the surface of solidified LBE.38 High magnification image is taken by Laser microscope.

Material Performance in Lead and Lead–Bismuth Alloy

13

Precipitation is essential to materials performance used in molten LA alloy because of dissolution of the main element as Ni, Fe, and Cr. Austenitic stainless steel include high Ni comparative with other element, ferritalization will occur in the surface contact with the molten alloy. As saturated concentration depends on temperature, temperature difference drives precipitation at cold leg part in the flowing system.

8

Weldment

Performance of the weld joint material is required to be the base material equivalent to or higher. Weld line location is determined by considering the environment in which materials are used. For example, in the proton beam window, high-energy protons bombardment must be avoided to be irradiated directly welded part since weld part will loss ductility to failure. Corrosion performance in Pb–Bi of weldment, F82H co-material of F/M steels was reported for the electron beam welding as well as JACA comaterial of austenitic stainless steel in the previous chapter. It was concluded that welds at 450 and 500 1C weld performance is equivalent to the base material in corrosion resistance. The investigation was done for the welded part and heat affected zone.48 Martín-Muñoz et al. also reported weld joint performance under a stagnant LBE corrosion test. T91–T91 weld jointed in the tungsten inert gas (TIG) condition at 775 K and 316L–316L weld jointed in the TIG condition at 725 K were assessed to have the same corrosion properties with parent materials. In addition dissimilar welded material, 316L–T91, dissolution process occurred characterized by a typical depletion of Ni at higher temperature, 825 K.64 Weisenburger et al. tested P122 (12Cr) F/M steel welded joint in TIG at 550 1C in the stagnant LBE condition and reported that welded joint are covered with protective oxide layer spinel as well as the parent material surface.65 Heinzel et al. reported the weldment performance on P91 TIG (tungsten inert gas welding), P91 EB (electron beam welding) and frictions stir welding, with P92 (EB), PM2000 (EB) and combination of P91–PM2000 EB, tested 2000 h in stagnant liquid Pb at 550 1C. PM2000 included 5.6 w% Al and 22% Cr w% included in the matrix. Co-materials of PM2000 welded joint makes thin Al rich oxide protective surface but P91–PM2000 EB dissimilar joint had a lot of precipitation.66 Welded joint is necessary to build devices and microstructure often shows different from the parent materials. In order to keep material performance equivalent to the parent material in the molten LA alloys use, EB weld makes rather flatter jointed surface than TIG weld. In TIG weldment it must be paid attention in the internal weld line where often shows a convex pattern that will disturb a flow velocity profile of a molten LBE and accelerate erosion.

9

Wetting

The advantage of the Pb–Bi use is that boiling point (1670 1C) is higher than the melting point of the structural material, the neutron absorption cross section is smaller than the mercury, and chemically it is stable as compared with sodium. The disadvantage is the compatibility with the materials at high temperature and the generation of radioactive isotopes polonium, alpha particle emitter, for nuclear transmutation. Except for physical properties of molten lead bismuth, engineering issues for use is how to suppress material corrosion. It can be mentioned that if wetting property is low, the corrosion of material interfaced with molten lead bismuth may not be generated easily and the heat transfer properties are not good qualitatively. High wetting property, however, may cause the corrosion of the material. The wettability of lead–bismuth and materials was measured. Detail of experiment was reported but for understanding simple description was stated as follows. In experiment, material plate was placed on the platinum plate, which was setup on a quartz rod and a portion of solid lead bismuth was put on there. Lead bismuth was dissolved to liquid by raising the temperature. The contact angle from the projection image by the CCD camera is measured by changing the temperature. As a typical example, cast iron4SS316L4aluminum, of a good wettability in the order as shown in Figure 10. That is, it can be considered that the corrosion resistance is increased to include aluminum in the materials or to cover the surface of the materials, which has the poor wetting properties. Wetting property is deeply related with corrosion, heat transfer performance from points of boundary condition views and liquid metal embrittlement of materials that contact with a molten LBE. Also it is essential conditions of the measurement to ensure the acoustic impedance between the piping material and molten Pb–Bi for keeping high signal level in the application of flow meter mechanism of acoustic waves.

10 10.1

Miscellaneous Issues Related to Materials Performance Equipment Specification

ADS, Accelerator-Driven nuclear transmutation System, consists of high-energy proton accelerator and fast neutron reactor. It is possible to apply the material technology for fast reactors to ADS because it is cultivated in the fast breeder reactors developed hitherto, although it can be said not completed.

14

Material Performance in Lead and Lead–Bismuth Alloy

Figure 10 Contacting angle between liquid LBE and materials, Al, SS316L, and cast iron.

Ferrite martensitic steel, oxide dispersion strengthened alloy with excellent high-temperature strength is a candidate material design as a fuel cladding material member. Unique member in ADS is a proton beam window that high-energy protons to pass through. Otherwise design without window is alternative case. Design requirement free from brittle fracture favors austenitic stainless steel as a candidate material. From the viewpoint of power generation efficiency, in a nuclear power reactor of the lead–bismuth cooling, coolant temperature is designed at about 550 1C. On the other hand, it is not always necessary to determine the high temperature if the purpose of processing of high-level nuclear waste, for example, less than 500 1C is considered. Major elements of the austenitic stainless steel are Fe, Cr, and Ni. These elements are dissolved in lead–bismuth eutectics. The solubility of Ni is higher than other two elements. Ni dissolution causes ferritization from austenitic structure at the interface between lead bismuth and steel. As an example of the application of the F/M steel to proton beam window, there was a spallation neutron source facility, called MEGAPIE, at Paul Scherrer Institute. Performs international joint experiment for the purpose of ADS material development was carried in 1999–2014. LBE temperature employed in the short term proton irradiation experiment, over 4 months (2006.8–12), was 230–320 1C. Materials used in this project were the FM steel, T91, for beam window and also austenitic stainless steel, SS316L, for other parts.

10.2

Thermal Parameters in Use

Design issues for lead bismuth use are thermal flow condition itself. Melting point of lead–bismuth is 124.5 1C for the case of lead 45 – bismuth 55 wt%. When used in a flow process, minimum process temperature for lead bismuth use can be said 200 1C roughly if considering the margin in order to prevent re-solidification due to the occurrence of cold spots in the fluid. When using a steam generator, it is 280 1C or higher from the condition of ensuring heat transfer efficiency. The flow rate, 2 m s
1 can be considered as erosion prevention, for example, as a provisional value of the mainstream velocity. An evaluation problem of erosion in the secondary flow and narrow portion.49,63

10.3

Drive of Molten Lead Bismuth

There are mainly two methods to drive molten lead bismuth. They are mechanical drive system due to the rotation force of the impeller and the drive system by inductive electromagnetic force. A mechanical pump technology has been established with paying attention to the resonance of the shaft and bearing system. It is possible to know the LBE flow rate in the fluid from the output and the rotational speed of the mechanical pump. Leakage prevention LBE from the sealing portion can be controlled by the system by the larger external pressure using inert gas than the internal pressure of the bearing portion. Loss of mass at the impeller of mechanical rotation mechanism is not an issue because often these parts is manufactured by casting iron thicker enough to keep its mechanical functions.

Material Performance in Lead and Lead–Bismuth Alloy

15

Electromagnetic pumps have been used for the driving force of industrial use, for example, molten metal as aluminum for manufacturing industrial products. The principle is to use electromagnetic force produced by inductive magnetic field and inductive current. The issue for molten lead bismuth use from points of views of materials engineering is a trapping effect for ferritic dust species dissolved into the flowing lead bismuth from steels.

10.4

Electromagnetic Flow Meters

Electromagnetic flow meters have been used conventionally for measuring the flow rate of the opaque liquid lead–bismuth. The principle of electromagnetic flow meter is to measure the electrostatic potential generated by LBE flowing in a magnetic field. Relationship between the flow rate and the generated voltage is calibrated before measurement quantitatively. The issue from material points of views is to keep a stable contacting between flowing lead bismuth and electrode material. Disturbing factors are wetting property change, erosion of electrode and slug attachment on the surface of electrode. Expansion of the flow channel, reduction of the flow channel, material erosion problems such as the occurrence of vortex and secondary flow, heat transfer characteristics of the beam window in ADS and flow profile around the reactor fuel cladding tube require the measurement technology on velocity field and flow rate. Ultrasonic technology can be applied to those requests from laboratories. Ultrasonic flow meter based on the principle of the propagation time difference method is to measure the time difference by the speed of sound7stream to output the ultrasound between the upstream and downstream from the relationship between the flow. Pulsed Doppler flow velocity meter developed by Takeda makes it possible to measure the velocity distribution of the flow path directly.69 In principle it is possible to convert by integrating it to the flow rate. It is essential conditions of the measurement to ensure the acoustic impedance between the piping material and molten Pb–Bi for keeping high signal level. Without changing the speed of propagation of sound waves in the material, it is necessary to improve the wettability.

10.5

Oxygen Concentration Environment

The need for the oxygen concentration control is to achieve a stable oxide film on the surface of the materials. The range is dependent on temperature and steels for use. Approximately it ranges from 10–6 to 10–4 mass%. If the oxygen concentration in the molten Pb–Bi is small, the base material of the steel is subjected to dissolution and desorption. If the oxygen concentration is too high, lead oxide PbO (melting point 886 1C) is formed, which may blockade the flow path. In ADS, the proton beam, hydrogen ion, is injected into the molten lead bismuth in a nuclear reactor through the beam window material. Chemical activity situation is reducing conditions. Oxygen dissolved in the lead–bismuth can be consumed in the oxidation film formation of the steel material. As a result, the oxygen concentration in the Pb–Bi moves in a direction to deplete. In the MEGAPIE experiment, oxygen concentration was evaluated low and temperature of the molten Pb–Bi was low. The degree of corrosion materials was evaluated to be very low. Measurement of the oxygen concentration was not performed and oxygen control was not also done. In fact at large Pb–Bi use device, the oxygen concentration in the Pb–Bi is considered as one of the monitoring items.

11

Outlook

For the use of LA as coolant and spallation target it is important that the materials properties compilations and databases are extended to include mechanical properties of structural materials in LA, such as the effect of temperature and strain rate,52 fracture toughness,25,53 weldment48,54,64–66 and liquid metal embrittlement.55 They are essential to the design work for the concepts of the ADS systems. Erosion–corrosion of materials in flowing LA should be considered along with details of the flow profile. It was recognized that magnetite in the oxide layer is eliminated in the steady-stately flowing LA. There is evidence of erosion detected in the expanded flow channel of the JLBL-1 test specimen.48,49,61 The eroded part of the specimen coincides with regions in flowing LA, such as secondary flow or vortex flow. Erosion also was found in the LINCE loop at 725K.63 These facts suggest to pay attention to flow profile in the circulating loop and working temperature. In the last decade, research projects for Accelerator Driven nuclear transmutation System (ADS), Lead-cooled Fast Reactor (LFR), MEGAwatt Pilot Experiment (MEGAPIE) and MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) were launched. In order to design the conceptual model of the real spallation target, the performance of neutronics, reactor physics and thermal hydraulics has been studied along with the materials performances in lead bismuth or lead. For the materials bombarded by high-energy particles such as proton beams, the surface coating or surface treatment, defect formation mechanism including not only corrosion but also the synergetic effect of irradiation field, must be understood. For the materials applicable to the cladding of fuel rod, Fe–Al alloys seem to be effective in the usage of LA, but optimum Al concentration must be determined.

16

Material Performance in Lead and Lead–Bismuth Alloy

Since the explosion of nuclear power stations in Fukushima, quest of disposal problem in the development of new technologies of high-level radioactive raw waste is closed up, accelerator-driven transmutation system, lead bismuth eutectics is to be used as coolant and spallation target material, has been attracting attention as one of them. Conclusively it is reported finally that a new facility for basic research on ADS is going on designing and constructing the facilities to receive high-energy proton beam from LINAC at J-PARC.

References 1. Sekimoto, H., 2001. Introductory remarks on liquid metal cooled fast reactors, In proceedings of the ISTC-TITech Japan Workshop on Nuclear Reactors Technologies in Russia/CIS, July 13. 2. Sekimoto, H., Ryu, K., Yoshimura, Y., 2001. CANDLE: The new burnup strategy. Nucl. Sci. Eng. 139, 306–317. 3. OECD/NEA, 2007. Nuclear Science Committee, Working Party on Scientific Issues of the Fuel Cycle, Working Group on Lead−bismuth Eutectic published Handbook on Lead−bismuth Eutectic Alloy and Lead Properties, Materials Compatibility, Thermal-hydraulics and Technologies (ISBN 978−92−64−99002−9). 4. Zhang, J., Li, N.J., 2008. Nucl. Mater. 373, 351–377. 5. Fazio, C., Alamo, A., Almazouzi, A., et al., 2009. European cross-cutting research on structural materials for Generation IV and transmutation systems. Journal of Nuclear Materials 392, 316–323. 6. Bauer, G.S., Salvatores, M., Heusen, G., 2001. MEGAPIE, a 1MW pilot experiment for a liquid metal spallation target. Journal of Nuclear Materials 296, 17–33. 7. Groeschel, F., Fazio, C., Knebel, J., et al., 2004. The MEGAPIE 1MW target in support to ADS development: status of R&D and design. Journal of Nuclear Materials 335, 156–162. 8. Wagner, Werner, Gröschel, Friedrich, Thomsen, Knud, Heyck, Hajo, 2008. MEGAPIE at SINQ − The first liquid metal target driven by a megawatt class proton beam. Journal of Nuclear Materials 377, 12–16. 9. Cinotti, L., Giraud, B., Ait Abderrahim, H., 2004. The experimental accelerator driven system (XADS) designs in the EURATOM 5th framework programme. Journal of Nuclear Materials 335, 148–155. 10. Knebel, J.U., Aït abderrahim, H., Benamati, G., et al., 2005. “IP EUROTRANS: A European Research Programme for the Transmutation of High-Level Nuclear Waste in an Accelerator-Driven System,” Proc. 8th Information Exchange Mtg. Actinide and Fission Product Partitioning and Transmutation, LasVegas, Nevada, November 9−11, 2004, Organization for Economic Co-operation and Development. 11. Mukaiyama, T., Takizuka, T., Mizumoto, M., et al., 2001. Review of research and development of accelerator-driven system in Japan for transmutation of long-lived nuclides. Progress in Nuclear Energy 38 (1−2), 107. 12. TSUJIMOTO, K., SASA, T., NISHIHARA, K., TAKIZUKA, T., TAKANO, H., 2000. Accelerator-driven system for transmutation of high-level waste. Progress in Nuclear Energy 37 (1−4), 339. 13. Oigawa, H. , Ouchi, N. , Kikuchi, K. , et al., 2003.“Research and Development Program on Accelerator Driven System in JAERI,” Proc. GLOBAL 2003, New Orleans, Lousiana, November 16−20, American Nuclear Society (2003). 14. Glasbrenner, H., Dai, Y., Groschel, F., 2005. LiSoR irradiation experiments and preliminary post-irradiation examinations. Journal of Nuclear Materials 343, 267–274. 15. Joris Van den Bosch, A.D.S.,2008. Candidate Materials Compatibility with Liquid Meal in a Neutron Irradiation Environment, Doctoral Thesis, ISBN 978−90−8578−241− 4, 7. 16. Sheffield, R. L. , pitcher, E. J, 2009. ADS History in the USA, Proceedings of AHIPa09.10, Fermi Labo. 17. Gohar, Y., Gohar, O.U.S.R.Y., 2009. Spallation target design for accelerator-driven systems, Proceedings of AHIPa09.10, Fermi Labo. 18. Eric, J. Pitcher, 2008. The materials test station: A fast-spectrum irradiation facility. Journal of Nuclear Materials 377, 17–20. 19. Gromov, B.F., Orlov, Yu. I., Martynov, O.N., Ivanov, K.D., Gulevsky, V.A., 1995. Physical-chemical principles of lead−bismuth coolant technology. In: Borgstedt, H.U., Frees, G. (Eds.), Liquid Metal Systems. New York: Plenum Press, pp. 339–343. 20. Martynov, P.N., Orlov, Yu. I., Efanov, A.D., et al., 2001. Technology of lead−bismuth coolants for nuclear reactors, Proc. of the ISTC-TITech Japan Workshop on Nuclear Reactor Technologies in Russia/CIS, 80−105. 21. OECD, 2007. Handbook on Lead−bismuth Eutectic Alloy and Lead Properties, Materials Compatibility, Thermal-hydraulics and Technologies 109. 22. Martinelli, L., Balbaud-Célérier, F., Terlain, A., et al., 2008. Oxidation mechanism of a Fe−9Cr−1Mo steel by liquid Pb−Bi eutectic alloy (Part I). Corrosion Science 50, 2523–2536. 23. Martinelli, L., Balbaud-Célérier, F., Terlain, A., et al., 2008. Oxidation mechanism of an Fe−9Cr−1Mo steel by liquid Pb−Bi eutectic alloy at 470 1 C (Part II). Corrosion Science 50, 2537–2548. 24. Martinelli, L., Balbaud-Célérier, F., Picard, G., Santarini, G., 2008. Oxidation mechanism of a Fe−9Cr−1Mo steel by liquid Pb−Bi eutectic alloy (Part III). Corrosion Science 50, 2549–2559. 25. Auger, T., Hamouche, Z., Medina-Almaza`n, L., Gorse, D., 2008. Liquid metal embrittlement of T91 and 316L steels by heavy liquid metals: A fracture mechanics assessment. Journal of Nuclear Materials 377, 253–260. 26. Tamura, M., Hayakawa, H., Tanimura, M., Hishinuma, A., Kondo, T., 1986. Development of potential low activation ferritic and austenitic steels. Journal of Nuclear Materials 141–143. 1067–1073. 27. Furukawa, T., Müller, G., Schumacher, G., et al., 2004. Journal of Nuclear Science and Technology 41, 265. 28. Tan, L., Machut, M.T., Sridharan, K., Allen, T.R., 2007. Corrosion behavior of a ferritic/martensitic steel HCM12A exposed to harsh environments. NUMA 371, 161–170. 29. Masuyama, F., 1998. New developments in steels for power generation boilers, In: Viswanathan, R., Nutting, J. (Eds.), Advanced Heat Resistant Steels for Power Generation, Conference Proceedings. San Sebastian, Spain, April 27. 30. Viswanathan, R., Bakker, W., 2001. Materials for ultrasupercritical coal power plants – Boiler materials: Part 1. Journal of Materials Engineering and Performance 10, 81–95. 31. Klenowicz, Z., Darowicki, K., 2001. Waste incinerators: Corrosion problems and construction materials – A review. Corrosion Reviews 19, 467–492. 32. Hosemann, P., Hawley, M.E., Koury, D., et al., 2008. Nanoscale characterization of HT-9 exposed to lead bismuth eutectic at 550 1 C for 3000 h. Journal of Nuclear Materials 381, 211–215. 33. Hosemann, P., Swadener, J.G., Welch, J., Li, N., 2008. Nano-indentation measurement of oxide layers formed in LBE on F/M steels. Journal of Nuclear Materials 377, 201–205. 34. Yamaki, E., Kikuchi, K., 2010. A stability of oxide scales formed in LBE on HCM12A to external loading. Journal of Nuclear Materials 398, 153–159. 35. Sugawara, T., Kikuchi, K., Nishihara, K., Oigawa, H., 2010. Investigation of beam window buckling with consideration of irradiation effects for conceptual ADS design. Journal of Nuclear Materials 398, 246–250. 36. Heinzel, A., Kondo, M., Takahashi, M., 2006. Corrosion of steels with surface treatment and Al-alloying by GESA exposed in lead−bismuth. Journal of Nuclear Materials 350, 264–270.

Material Performance in Lead and Lead–Bismuth Alloy

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37. Muller, G., Schumacher, G., Zimmermann, F., 2000. Investigation on oxygen controlled liquid lead corrosion of surface treated steels. Journal of Nuclear Materials 278, 85–95. 38. Weisenburger, A., Heinzel, A., Muller, G., Muscher, H., Rousanov, A., 2008. T91 cladding tubes with and without modified FeCrAlY coatings exposed in LBE at different flow, stress and temperature conditions. Journal of Nuclear Materials 376, 274–281. 39. Muller, G., Heinzel, A., Konys, J., et al., 2004. Behavior of steels in flowing liquid PbBi eutectic alloy at 420–600 1 C after 4000–7200 h. Journal of Nuclear Materials 335, 163–168. 40. Takaya, S., Furukawa, T., Aoto, K., et al., 2009. Corrosion behavior of Al-alloying high Cr-ODS steels in lead−bismuth eutectic. Journal of Nuclear Materials 386−388, 507–510. 41. Hosemann, P., Thau, H.T., Johnson, A.L., Maloy, S.A., Li, N., 2008. Corrosion of ODS steels in lead−bismuth eutectic. Journal of Nuclear Materials 373, 246–253. 42. Dai, Y., Henry, J., Auger, T., et al., 2006. Assessment of the lifetime of the beam window of MEGAPIE target liquid metal container. Journal of Nuclear Materials 356, 308–320. 43. Nishihara, Kenji, Kikuchi, Kenji, 2008. Irradiation damage to the beam window in the 800MWth accelerator-driven system. Journal of Nuclear Materials 377, 298–306. 44. Dai, Yong, Wagner, Werner, 2009. Materials researches at the Paul Scherrer Institute for developing high power spallation targets. Journal of Nuclear Materials 389, 288–296. 45. Tanaka, M.P., Hamada, S., Hishinuma, A., Grossbeck, M.L., 1988. Post irrdiation tensile and fatigue behavior of Austenitic PCA stainless steels irradiated in HFIR. NUMA 155−157, 957–962. 46. Barbier, F., Rusanov, A., 2001. Corrosion behavior of steels in flowing lead−bismuth. J. Nucl. Mater. 296, 231. 47. Muler, G., Heinzel, A., Koney, J., et al., 2002. J. Nucl. Mater. 301, 40. 48. Kikuchi, K., Kamata, K., Ono, M., Kitano, T., Hayashi, K., Oigawa, H., 2008. Corrosion rate of parent and weld materials of F82H and JPCA steels under LBE flow with active oxygen control at 450 and 500 1 C. Journal of Nuclear Materials 377, 232–242. 49. Kikuchi, K., Saito, S., Kurata, Y., et al., 2004. Lead−Bismuth Eutectic Compatibility with Materials in the Concept of Spallation Target for ADS. JSME International Journal Series B 47 (2), 332–339. 50. Zhang, Jinsuo, Li, Ning, 2004. Corrosion/precipitation in non-isothermal and multi-modular LBE loop systems. Journal of Nuclear Materials 326, 201–210. 51. Kikuchi, K., Saito, S., Hamaguchi, D., Tezuka, M., 2010. Ni-rich precipitates in a lead bismuth eutectic loop. Journal of Nuclear Materials 398, 104–108. 52. Van den Bosch, J., Sapundjiev, D., Almazouzi, A., 2006. Effects of temperature and strain rate on the mechanical properties of T91 material tested in liquid lead bismuth eutectic. Journal of Nuclear Materials 356, 237–246. 53. Van den Bosch, J., Coen, G., Almazouzi, A., Degrieck, J., 2009. Fracture toughness assessment of ferritic−martensitic steel in liquid lead−bismuth eutectic. Journal of Nuclear Materials 385, 250–257. 54. Van den Bosch, J., Almazouzi, A., 2009. Compatibility of martensitic/austenitic steel welds with liquid lead bismuth eutectic environment. Journal of Nuclear Materials 385, 504–509. 55. Auger, T., Serre, I., Lorang, G., et al., 2008. Role of oxidation on LME of T91 steel studied by small punch test. Journal of Nuclear Materials 376, 336–340. 56. C. Rubbia, J.A. Rubio, S. Buono, et al., 1995. Conceptual Design Of A Fast Neutron Operated High Power Energy Amplifier, CERN/AT/95−44 (ET). 57. Müller, G., Schumacher, G., Zimmermann, F., 2000. Investigation on oxygen controlled liquid lead corrosion of surface treated steels. Journal of Nuclear Materials 278, 85–94. 58. Schroer, C., Wedemeyer, O., Skrypnik, A., Novotny, J., Konys, J., 2012. , Corrosion kinetics of Steel T91 in flowing oxygen-containing lead−bismuth eutectic at 4501 C. Journal of Nuclear Materials 431, 105–112. 59. Kikuchi, K., Khalid Rivai, A., Saito, S., Michael Bolind, A., Kogure, A., 2012. HCM12A oxide layer investigation using scanning probe microscope. Journal of Nuclear Materials 431, 120–124. 60. Rebelo de Figueiredo, M., Kikuchi, K., Hosemann, P., 2012. Oxide-Metal Interfaces Strength Measurements on Passive Films Formed in Heavy Liquid. Microscopy and Microanalysis 18 (Suppl 2), doi:10.1017/S1431927612005788. 61. Saito, S., Kikuchi, K., Hamaguchi, D., et al., 2012. Corrosion−erosion test of SS316L grain boundary engineering material (GBEM) in lead bismuth flowing loop. Journal of Nuclear Materials 431, 91–96. 62. Rivai, A.K., Saito, S., Tezuka, M., Kato, C., Kikuchi, K., 2012. Effect of cold working on the corrosion resistance of JPCA stainless steel in flowing Pb−Bi at 450 1 C. Journal of Nuclear Materials 431, 97–104. 63. Martín-Muñoz, F.J., Soler-Crespo, L., Gómez-Briceño, D., 2011. Corrosion behaviour of martensitic and austenitic steels in flowing lead−bismuth eutectic. Journal of Nuclear Materials 416, 87–93. 64. Martín-Muñoz, F.J., Soler-Crespo, L., Gómez-Briceño, D., 2011. Assessment of the influence of surface finishing and weld joints on the corrosion/oxidation behaviour of stainless steels in lead bismuth eutectic. Journal of Nuclear Materials 416, 80–86. 65. Weisenburger, A., Aoto, K., Müller, G., et al., 2006. Behaviour of chromium steels in liquid Pb−55.5Bi with changing oxygen content and temperature. Journal of Nuclear Materials 358, 69–76. 66. Heinzel, A., Müller, G., Weisenburger, A., 2013. Behavior of welds in liquid lead containing 10−6 wt% and 10−8 wt% oxygen. JNM 437, 116–221. 67. Ellingham, H.J.T., 1944. J. Soc. Chem. Ind. Trans. 63, 125–133. 68. Kikuchi, K., Okada, N., Kato, M., Uchida, H., Saito, S., 2014. HCM12A Cr-rich oxide layer investigation using 3D atom probe. Journal of Nuclear Materials 450, 237–243. 69. Kikuchia, K., Takeda, Y., Obayashi, H., Tezuka, M., Sato, H., 2006. Measurement of LBE flow velocity profile by UDVP. Journal of Nuclear Materials 356, 273–279. 70. Abad, M., Parker, S., Frazer, D., et al., 2015. Evaluation of the mechanical properties of naturally grown multilayered oxides formed on HCM12A using small scale mechanical testing. Oxidation of Metals 84, 211–231.