Thermochemical energy storage systems from carbonates, mainly those based on calcium carbonate, have been gaining momentum in the last few years. However, despite the considerable interest in the process, the Technology Readiness Level (TRL) is still low. Therefore, facing the progressive development of the technology at different scales is essential to carry out a comprehensive risk assessment and a Failure Mode Effect and Analysis (FMEA) process to guarantee the safety and operation of the technology systems. In this study, the methodology was applied to a first-of-its-kind prototype, and it is a valuable tool for assessing safe design and operation and potential scaling up. The present work describes the methodology for carrying out these analyses to construct a kW-scale prototype of an energy storage system based on calcium carbonate. The main potential risks occur during the testing and operation stages (>50% of identified risks), being derived mainly from potential overheating in the reactors, failures in the control of the solar shape at the receiver, and potential failures of the control system. Through the assessment of Risk Priority Numbers (RPNs), it was identified that the issues requiring more attention are related to hot fluid path to avoid loss of heat transfer and potential damages (personal and on the facilities), mainly due to their probability to occur (>8 on a scale of 10). The results derived from the FMEA analysis show the need for specific control measures in reactors, especially in the calciner, with high operation temperatures (1000 °C) and potential effects of overheating and corrosion.