Following the Fukushima accident, safety has become an even more critical aspect in the design of the new generation of nuclear reactors. The ARTRUIM reactor design, a loop-type Sodium-cooled Fast Reactor (SFR), stems from this necessity. One of the key feature of this concept, introduced to meet the required safety standards, is the design of a compact and passive Decay Heat Removal System (DHRS). This component is tasked with storing the excess heat from the nuclear core during an emergency shut down, operating without external intervention for multiple days. To ensure the system's compactness, the design choice fell onto a modular storage, where the metallic Phase Change Material (PCM) Zamak (Zn-4%Al), selected to store the excess thermal heat, is encapsulated in multiple SS430 boxes.

In working condition, the encapsulated Zamak will first interact mechanically with the walls of the box, then it will undergo phase change (i.e. melting), that will lead to thermochemical reactions. This study has started from characterization of the materials individually, by conducting measurements of the heat capacity and latent heat values involved in the evolution of the system by Differential Scanning Calorimetry (DSC, Netzsch Jupiter F3). To investigate the thermochemical interactions, the microstructure of Zamak and SS430 is also observed after the two materials were put into contact and brought to working temperatures. This process of melting Zamak on SS430 will also allow the assessment of the wetting angle resulting from their interaction. Alongside the experimental campaign to characterize the two materials and their interactions, a numerical model was developed, incorporating the experimental data to accurately represent the materials and the effects of their interactions.

To further explore the behaviour of the system, an elementary unit box and the reciprocal numerical model is under development. In the experimental setup, IR thermography is used to observe the temperature distribution of the representative box, enabling the quantification of thermochemical interactions and determination of the system's thermophysical properties.