Corrosion of structural materials by liquid metals used fusion, fission and spallation

J.-L. Courouau (1) , D. Feron (1)

1 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)

Liquid metals (lithium, sodium, lead and its liquid alloys Pb-Li or Pb-Bi) are used as coolants for fusion, fission or spallation reactors due to their thermal and nuclear properties. However, these liquid metals are corrosive when they come into contact with solid metallic materials. Preserving structural alloys (no- and low alloyed steels, stainless steels, nickel based alloys) in contact with these liquid metals requires the knowledge of the corrosion phenomena that may occur mainly liquid metal embrittlement and general corrosion with mass transfer. Liquid metal embrittlement is a particularly case of stress corrosion cracking in liquid metals which results in a decrease of the toughness or the ductility of the structural materials. It is also known as liquid metal cracking. Under specific combination of liquid metals, stressed solid metals or alloys and temperatures, an intergranular cracking of the solid alloys is sometimes observed. If wetting is a key factor, temperature, stress and strain rates, solid and liquid metal compositions are also influencing factors. Some results are shown with susceptible couples like ferritic/martensic steels in liquid lead (or its eutectics Pb-Li or Pb-Bi), and with also non susceptible couples like austenitic stainless steels in liquid sodium.General corrosion mechanisms in liquid metals is governed by thermodynamics and may be divided into two main phenomena et61485;Reaction with impurities dissolved oxygen in the liquid metal leads to oxidation of the solid metal when the reaction is thermodynamically possible and may lead to some protective oxide layers. If the activities of carbon (and other soluble elements like nitrogen) in the liquid and in the solid metals are different, carburation or de-carburation of the solid metals may occur, mainly at high temperature (above 600DC) as these phenomena are linked to the diffusion properties.et61485;Dissolution of the solid metal into the liquid metal may occur also and it is the main general corrosion phenomena when oxidation is not possible. The dissolution of alloying elements is function of their solubility in the liquid metal as nickel is very soluble in liquid lithium, liquid sodium or liquid lead, nickel alloys are not suitable for these environments where temperature and flow rates are also important parameters. The alloys containing some nickel, like austenitic stainless steels, will undergo ferritization of the dissolution zone due to the loss of nickel which is an austenite stabilizer. These phenomena show that the chemistry of the liquid metal is a key parameter for general corrosion of structural materials. As the solubility is generally decreasing with temperature, mass transfer may play also an important role in non-isothermal systems with dissolution process in the hottest section and precipitation in the coldest part of the circuits.If sodium does corrode, these phenomena are considered today under control for austenitic steels. For liquid lead and its liquid alloys, corrosion of steels, including liquid metal embrittlement, are important issues which need mitigation strategies including coatings or the development of specific alloys (steels forming a self-healing protective alumina layer) for instance.

Mots clés: liquid metals; sodium; lead; lead-bismuth; stainless steel; corrosion

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique Nucléaire Théorique [nucl-th]

J.-L. Courouau, D. Feron. Corrosion of structural materials by liquid metals used fusion, fission and spallation. 1st IAEA Workshop on Challenges for coolants in fast spectrum system, Jul 2017, Vienne, Austria. ⟨hal-02417812⟩