Risk analysis and reliability of the GERDA Experiment extraction and ventilation plant at Gran Sasso mountain underground laboratory of Italian National Institute for Nuclear Physics

Mara Lombardi,Antonio Giampaoli,Massimo Guarascio,Mafalda Musti,Roberto Tartaglia,Roberto Perruzza,Maria Teresa Ranalli,Enzo Paolo Giovannone,Fabio Garzia

doi:10.1590/0370-44672016700141

Abstract

Abstract The aim of this study is the risk analysis evaluation about argon release from the GERDA experiment in the Gran Sasso underground National Laboratories (LNGS) of the Italian National Institute for Nuclear Physics (INFN). The GERDA apparatus, located in Hall A of the LNGS, is a facility with germanium detectors located in a wide tank filled with about 70 m3 of cold liquefied argon. This cryo-tank sits in another water-filled tank (700 m3) at atmospheric pressure. In such cryogenic processes, the main cause of an accidental scenario is lacking insulation of the cryo-tank. A preliminary HazOp analysis has been carried out on the whole system. The risk assessment identified two possible top-events: explosion due to a Rapid Phase Transition - RPT and argon runaway evaporation. Risk analysis highlighted a higher probability of occurrence of the latter top event. To avoid emission in Hall A, the HazOp, Fault Tree and Event tree analyses of the cryogenic gas extraction and ventilation plant have been made. The failures related to the ventilation system are the main cause responsible for the occurrence. To improve the system reliability some corrective actions were proposed: the use of UPS and the upgrade of damper opening devices. Furthermore, the Human Reliability Analysis identified some operating and management improvements: action procedure optimization, alert warnings and staff training. The proposed model integrates the existing analysis techniques by applying the results to an atypical work environment and there are useful suggestions for improving the system reliability.

Highlights

IntroductionTo improve safety one has to know where the risks are (Pasman et al, 2009)
Roberto TartagliaAccording to many authors, to improve safety one has to know where the risks are (Pasman et al, 2009)
To improve safety one has to know where the risks are (Pasman et al, 2009). This is certainly true when it is necessary to design the safety of complex systems, where the predictive analysis of failure modes requires identification of the hazardous conditions, to quantify their probability of occurrence and to define representative accident scenarios. The representativeness of these scenarios is subject to the knowledge of production processes and system parts and the quantitative risk analysis requires that all failure events be considered (Zhao et al, 2016)

Summary

Introduction

To improve safety one has to know where the risks are (Pasman et al, 2009) This is certainly true when it is necessary to design the safety of complex systems, where the predictive analysis of failure modes requires identification of the hazardous conditions, to quantify their probability of occurrence and to define representative accident scenarios. From the accidental risk analysis, during the identification phase, a pressure rise in the cryostat over the design value (a) and exceeding of the containment and insulation conditions (b) of the cryogenic liquid was identified and it was possible to identify a dominating critical scenario due to a mixing of the shielding water of the Water Tank with the cryogenic liquid (LAr), which leads to an explosive effect due to Rapid Phase Transition (RTP) This mode can be considered as a critical sub system of containment loss (mixture of LAr and Water)

Objectives

Methods

Results

Conclusion