Experimental and numerical study of constrained melting of metallic phase change material (PCM)

The ATRUIM reactor design, a loop-type Sodium-cooled Fast Reactor (SFR), stems for the necessity of enhanced safety. One of the key safety features of this concept 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 and electricity for multiple days. To ensure the system’s compactness, the design choice fell onto a modular storage, where the metallic PCM selected to store the excess thermal heat, Zamak (Zn-4%Al), is encapsulated in multiple SS430 boxes.

In working condition, the PCM will undergo a solid-liquid phase change while in contact with the inside walls of the stainless steel box. In order to develop a representative CFD model to describe the phase change of Zamak and its mechanical and chemical interactions with the walls, the material properties and behaviours under transient melting conditions must be investigated. At laboratory scale, some necessary experimental measurements have been performed (TMA, DSC) to obtain the physical and chemical parameters required to characterize the materials and their sensibility in the numerical model.

An experimental setup representative of the elementary unit box of the DHRS is built to validate the CFD model at a larger scale (25x15x15cm). Since the PCM is enclosed in the box, it is not possible to directly observe the melting process. One of the possible ways explored to follow the position of the melting front is to reconstruct it using inverse method by recording the temperature map of the outside of the box with IR imaging and correlating it to the temperature simulated according to the thermal conditions inside the box.

The CFD physics’ models employed have shown good capabilities of simulating the phase change process. The experimental campaign on material characterization and on the setup representative of the elementary unit box will continue.

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