Juergen Konys

Development of oxygen meters for the use in lead-bismuth

Liquid lead and the eutectic lead-bismuth alloy (PbBi) are considered both as a spallation target and coolant of an accelerator driven system (ADS) for the transmutation of long-lived actinides from nuclear waste into shorter living isotopes. It is known that both, pure lead and PbBi, exhibit a high corrosivity against austenitic and ferritic steels, because of the high solubility of nickel and iron in PbBi. One way of reducing the strong corrosion is the in situ formation of stable oxide scales on the steel surfaces. Thermodynamic calculations and experimental results have confirmed, that the control of oxygen in lead or PbBi within a defined activity range can lead to acceptable corrosion rates. To control the level of oxygen dissolved in lead or PbBi, a sensor for measuring the oxygen activity is required. Within the sodium fast breeder reactor development, an adequate technique was established for estimating oxygen in liquid sodium. This knowledge can be used for other metal/oxygen systems like oxygen in PbBi. For measuring the oxygen activity and calculating its concentration, the relevant thermodynamic and solubility data have to be considered. Two reference electrode systems: Pt/air and In/In 2 O 3 (both based on yttria-stabilized zirconia as solid electrolyte) are investigated to evaluate their electromotive force (EMF)-temperature dependency in saturated and unsaturated oxygen solutions. Results with both types of oxygen meters in PbBi at different oxygen levels were compared with theoretical calculations. The experimental data indicate that the design, construction and integration of an oxygen control unit in a large scale PbBi-loop seems to be very feasible.

Corrosion of ferritic–martensitic steels in the eutectic Pb–17Li

Abstract Three different ferritic–martensitic steels were exposed to Pb–17Li under dynamic conditions at 480°C up to 8000 h. On the surface of all 7–10% Cr reduced-activation steels, a two-layer oxide scale consisting of MnCr 2 O 4 spinel and (Fe,Cr) 2 O 3 formed during the heat treatment. This was detected by means of XPS and AES analysis. It was found that the corrosive attack started with the dissolution of MnCr 2 O 4 spinel and (Fe,Cr) 2 O 3 . When the oxide scale was dissolved by the liquid metal the corrosive attack continued into the steel matrix. Investigations of the corrosion mechanism have revealed that the steel elements Fe and Cr were strongly dissolved. Those steel elements, which have a low solubility in Pb–17Li, like W, Mo, V, remained in the matrix and were enriched in the surface near layer.

Quantification of the Long-Term Performance of Steels T91 and 316L in Oxygen-Containing Flowing Lead-Bismuth Eutectic at 550°C

The long-term performance of ferritic/martensitic steel T91 and austenitic 316L in oxygen-containing flowing lead-bismuth eutectic at 550°C was investigated by exposing the materials for up to 15,000 h in the CORRIDA loop. The velocity of the liquid-metal flow was 2 m/s and the concentration of dissolved oxygen averaged 1.6 × 10 -6 mass %. The resulting corrosion processes and products were analyzed and quantified using metallographic methods.

Investigations on the transformation behavior of the intermetallic phase (Fe, Cr)2Al5 formed on MANET II steel by aluminizing

The present work describes investigations on the transformation behavior of the intermetallic phase (Fe, Cr)2Al5 which forms on martensitic 10%Cr steel during aluminizing. In order to improve the mechanical properties of the coating and to incorporate the metallic Al overlayer, a subsequent heat treatment is necessary after aluminizing. Heat treatments were carried out in Ar at 700°C and 1075°C for several exposure times. It was found at 700°C that the (Fe, Cr)2Al5 scale starts to transform into the softer (Fe, Cr)Al phase (referring to hardness) at the scale-substrate interface. This process is time dependent. The (Fe, Cr)Al phase gets further transformed into the α-Fe(Cr, Al) solid solution. After heat treatment at 1075°C for 0.5 h the (Fe, Cr)2Al5 scale is completely transformed. The resulting scale can be subdivided into an upper layer of (Fe, Cr)Al phase, an intermediate band of pores and a lower layer of α-Fe(Al, Cr) solid solution.

Scale structure of aluminised Manet steel after HIP treatment

Abstract Coatings on low activation steels are required in fusion technology in order to reduce the tritium permeation rate through the steel into the cooling water system by a factor of at least 100. Alumina seems to be a promising coating material. However, an appropriate coating system must also have the potential for self-healing since the ceramic alumina scale tends to fail if mechanical stress is applied. A technology is introduced here to form a ductile Al enriched surface scale on Manet II steel (Fe-10.3%Cr) with an alumina overlayer. This technology consists of two main process steps. Hot dip aluminising has been performed at 700°C for 30 s in order to introduce Al to the near surface zone. The very hard intermetallic scale Fe 2 Al 5 which forms during the immersion process gets completely transformed into FeAl 2 , FeAl and α-Fe(Al) phases during a subsequent hot isostatic press (HIP) process step at high pressure at 1040°C for 30 min. The pressures chosen for the HIPing were 1000 and 2000 bar. Without HIPing pores form due to the Kirkendall effect. The influence of the high pressure on the heat treatment (1040°C, 30 min) will be discussed in this paper.

Comparison of microstructure and formation of intermetallic phases on F82H-mod. and MANET II

Abstract This paper describes investigations on the formation and transformation of aluminde phases on F82H-mod. steel and for comparison on MANET II, as reference materials. In order to achieve the desired mechanical properties of both steels, a fully martensitic microstructure has to be adjusted by a special heat-treatment. For the improvement of the microstructure of the Al based permeation barrier, a heat treatment after hot dip aluminising is necessary as well. To meet both requirements, heat treatments at different temperatures (700°C/100 h or 1075°C/0.5 h for MANET II and F82H-mod.) were performed for comparison after hot dipping, followed by a subsequent annealing at 750°C for 2 h. At the highest temperature, the perfectly adhering aluminide scale can be subdivided into an upper FeAl phase, an intermediate band of pores and a lower part of α-Fe(Al) solid solution phase. Differences in microstructure and phase composition between MANET II and F82H-mod. are described by microanalytical techniques.

Aspects of Minimizing Steel Corrosion in Liquid Lead-Alloys by Addition of Oxygen

The concept of minimizing steel corrosion in liquid lead-alloys by addition of oxygen strongly depends on the availability of efficient devices for oxygen transfer and reliable oxygen sensors. The accuracy of electrochemical oxygen sensors is analyzed on the basis of theoretical considerations and results from experiments in stagnant lead-bismuth eutectic (LBE). Additionally, the feasibility of gas/liquid oxygen-transfer and the long-term performance of electrochemical sensors in flowing liquid metal are addressed based on operation of the CORRIDA loop, a facility for testing steels in flowing LBE.Copyright