This report describes the activities performed so far according to the plan for task 10.4:” Supercritical fluids as refrigerants”. The project aims at defining the feasibility of future detector cooling systems based on refrigerant in supercritical state. The present document summarises the main achievements at this stage: Review of the literature available regarding thermal efficiency studies with carbon dioxide at supercritical state. Selection of the best suited supercritical refrigerant candidate for low temperature applications. Final designs of two dedicated test stands and description of the processes.