Monte Carlo reliability analysis of a safety plant of the Italian Gran Sasso high energy physics national laboratory by means of the MARA code

The Gran Sasso National Laboratory (LNGS) of the Istituto Nazionale di Fisica Nucleare (INFN), the Italian government agency for nuclear physics, is the biggest underground physics laboratory in the world. The Laboratory is located inside the left motorway tunnel crossing the Gran Sasso mountain in the motorway connecting Rome to Teramo in central Italy. The Laboratory consists of three big Halls, connected through a network of tunnels, where nuclear physics experiments are performed. The unique access of the Laboratory is through the left motorway tunnel. The physics experiments run inside the Laboratory involve the use of considerable quantity of flammable, toxic and other dangerous materials that in case of an accident could pose hazards to the personnel as well as to the highway users. This situation requires that detailed safety analyses be made in order to evaluate the risk associated to the experimental activities and that state-of the-art safety systems be installed for prevention of accident occurrences, early accident detection, warning and protection so as to minimize the consequences of an accident inside the Laboratory. Then, reliability and availability analyses of the safety systems are mandatory in order to keep the control of their overall performance. In this paper we present the results of a Monte Carlo reliability analysis activity which was performed on the high-expansion foam fire-fighting safety system installed in one of the main halls of the Laboratory. The analysis was carried out by means of the MARA (Montecarlo Availability Reliability Analysis) code.