The ambitious goal of achieving Net-Zero energy targets in European countries by 2050 necessitates a significant increase in the penetration of renewable energy in the electrical grid. This transition is essential to decarbonising key sectors that contribute to greenhouse gas emissions. However, the rapid growth of renewable power generation presents challenges to maintaining grid flexibility, as current energy storage technologies, such as electrochemical batteries, face scalability limitations due to high costs associated with extended storage durations and increased capacity. In this context, there is a critical need for cost-effective, long-duration energy storage technologies to ensure a smooth transition to a Net-Zero future. This paper investigates the discharging performance of a novel Molten Salt/Slags Packed Bed Thermal Energy Storage (TES) technology within a Power-to-Heat-to-Power (P2H2P) Carnot Battery concept, leveraging supercritical CO2 Brayton cycles. A Computational Fluid Dynamics (CFD) model of the thermocline-based TES technology is developed and validated against experimental data from the literature. The validated model is then employed to assess the discharging performance of the TES tank under the boundary conditions dictated by the P2H2P/CB concept. A key focus of this study is monitoring the thermocline thickness and its impact on the discharging outflow temperature, which typically declines after a specific discharging duration. The TES system demonstrates an estimated Round-Trip Efficiency (RTE) of up to 90%. Moreover, this TES technology incorporates industrial waste as filler materials, specifically steel slags, which could be beneficial in regard of increased energy storage density and potentially cost reduction.