Design of fault trees as a practical method for risk analysis of CCS: Application to the different life stages of deep aquifer storage, combining long-term and short-term issues

INERIS (French National Institute for Industrial Environment and Risks) is involved in assessing accidental and chronic risks in industrial or underground activities. Concerning carbon dioxide storage, INERIS performs integrated risk assessment studies, by integrating both its know-how in industrial safety and the knowledge developed in the context of other underground storages: hydrocarbons, landfill, nuclear waste. Concerning the future development of the CCS technology, a major question is the underground evolution of the CO2 at medium and long time scales. It is necessary to undertake a systemic approach in order to consider all targets at stake and all stages of the CCS chain. INERIS developed a specific method that includes the tools that are used in environmental, health and safety risks. At first, a risk analysis was performed, leading to identify the relevant risk scenarios. There we took into account the possible high content of impurities, and therefore the different exposure routes for man and for the soil/water environment. 8 main “Impacting phenomena” were defined, they cover the whole CCS chain (capture, transport, injection and long-term storage) and include both accidental and long-term effects. Each Impacting phenomenon gets a series of causes, that were represented in fault trees and were described in a dynamic graph through an adequate software tool. In a second step, the risk scenarios are to be quantified in terms of transfer and effects to the environment, and the estimated flows are to be compared to critical flows. This overall method consists of an integrated risk assessment, and helps in managing the risk for all life stages and all elements of the CCS chain, either at surface level or in the underground.