# Design of the CIEMAT Corrosion Loop for Liquid Metal Experiments
###### Abstract  
The main components of a liquid breeder blanket in a fusion power reactor are lead lithium alloy (PbLi) and the steel structure in which the liquid is enclosed (EUROFER). Several compatibility tests have shown that structural materials always suffer from corrosion attacks. The governing mechanism can be attributed to the dissolution of the steel by the liquid breeder and is strongly related to the PbLi chemistry, velocity profile, and temperature. A new facility, CICLO-C (CIEMAT Corrosion Loop, Internally Coated), is dedicated to the study of corrosion in materials under the severe breeding blanket condition. An effort was made to design an experimental facility with a specific test section able to work at quite ambitious operation parameters: up to 550 \({}^{\circ}\)C and a 1 m/s flow of PbLi. Furthermore, an innovative tantalum coating was introduced in the whole loop to avoid impurities coming from the pipeline, which can disturb the measurements, and to better preserve the installation. breeder blanket; liquid metal; materials compatibility; high-temperature corrosion; coatings +
Footnote †: journal: Applied  
tritium breeder, a neutron multiplier, and a tritium carrier, hence playing an important role in reactor operation. The advantages of using PbLi are due to the nuclear properties of the eutectic (since the breeder and neutron multiplier are combined in the same material) and the chemical properties (since the eutectic does not exhibit an explosive reaction when in contact with air and water) [6,7]. The main drawback is its compatibility with materials due to its high corrosion grade. Corrosion can result in significant material thinning/wastage and the deposition of corrosion products, which may cause severe flow restrictions and excessive accumulation of radioactive material in unshielded regions. Within the European Fusion Technology Program, much effort has been placed on developing appropriate steels because of safety requirements, as it is mandatory to minimize problems associated with induced radioactivity in the structural materials. Several ferritic-martensitic steels, such as MANET, OPTIFER, F82H, CLAM, and so on, have been developed worldwide. The progress of the research activities in Europe has resulted in the formulation of the RAFM steel named EUROFER (9% Cr, 1% WVTa) [8]. The implementation of structural materials in blanket applications required a detailed study on chemical compatibility with a special focus on corrosion behavior. Considering that the structural material must maintain its integrity under large temperature gradients, severe thermal cycling, and intense irradiation, the compositional and microstructural changes due to selective dissolution and intergranular corrosion can lead to material failures [9]. The former consequence results in a loss of mechanical integrity, the creation of several impurities flowing in the system, and consequent load losses that increase the requirements for pumping power, decreasing the energy conversion efficiency and complicating system maintenance [10]. Several experiments have been performed over the past years in different international facilities, focusing on various aspects of PbLi flow and its interaction with structural and functional materials for fusion applications [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]. Although a good understanding of lithium lead behavior has been achieved, many compatibility problems with EUROFER as a structural material are still unresolved, especially in several blanket relevant conditions. These include cases of a high lithium lead flow rate together with a high temperature [21], chemical compatibility with coating materials [22], or the effect of radiation on the corrosion layer [23]. The changing experimental conditions have demonstrated that the corrosion attack can drastically change when the temperature changes at a given flow velocity [24], both of which are very important parameters for EUROFER corrosion dynamics.