Nitrogen gas spillage in a confined space located in the Gran Sasso Underground Nuclear Physics Laboratory: an outstanding oxygen deficiency hazard case study

Abstract

This paper deals with the cryogenic risk arising from nitrogen spillage in a box located in Hall A of the underground laboratories of the Gran Sasso National Laboratory, Assergi (L'Aquila). This box will be used as a storage area for some sensitive material (crystals) which will be used for an experiment called "CUORE". Starting from the Fault Tree Analysis (FTA), in order to estimate the global risk for human activities, a consequence analysis has been performed, using EFFECTS software models. The gap between the latest and the real scenario has been covered by a real test during which a "monitored, measured and controlled" gas nitrogen flow has been spilled into the box. Furthermore, a description of a reliable base for computational fluid dynamics (CFD) analysis is treated.

A Near Field–Far Field model for assessing Oxygen Deficiency Hazard

“…Regarding the case where the limit value for the oxygen concentration is equal to 15 % ( Figure 5), the NF does not reach the dimension of the working environment during the entire simulation time of 90 min. This result is in accordance with the one obtained in the real test in Bonfini et al (2013). At the end of simulation, the distance (i.e.…”

“…The real test in Bonfini et al (2013) highlights that the sensor detects an oxygen concentration of 17 % after about 24 min. Thus, our NF-FF model is the best performing since it is the closest to the reality: differently from the other models, the NF-FF model reaches the measured value of oxygen concentration, even if with some minutes of delay.…”

“…In all figures there are two y-axes, the left one represents the order of magnitude of the volume for the NF, while the one on the right the order of magnitude of the volume for the FF. The common assumptions for applying our NF-FF model in the case studies proposed by Augustynowicz (1993), Bonfini et al (2013), and Delayen et al (2001) are: C N2,we (0) = C N2,oe (0) = 79 %; C O2,we (0) = C O2,oe (0) = 21 %; T we (0) = T oe (0) = 293.15 K; T ig,a (0) = 293.15 K; P ig,a;s,j,i (0) = 1; R = 8.314472 J K -1 mol -1 . We assumed that outdoor parameters, such as pressure, temperature, and air composition, are constant in time.…”

“…Case study of Bonfini et al (2013) Bonfini et al (2013 present an oxygen deficiency case study in a box used as a storage area and located in the underground laboratories of the Italian Gran Sasso Nuclear Physics Laboratory. Their case study compare the trends of oxygen concentration obtained through the application of their theoretical approach based on the version published in 2009 of the model of Fermilab (Fermilab, 2009), a real test, and a Computational Fluid Dynamics (CFD) simulation.…”

“…With reference to this case, the NF-FF model provides the results depicted in Figure 4 and Figure 5, assuming a limit value for the oxygen concentration equal to 17 % and 15 %, respectively. We have chosen these limits because they represent two significant concentrations in the real test in Bonfini et al (2013): an oxygen concentration of 17 % is the minimum oxygen concentration reached after about 24 min, while an oxygen concentration of 15 % represents a concentration that is never reached. The flow rate of the nitrogen spilled using gas bottles is equal to 0.375 m 3 s -1 , continuously from the time instant 0 min to the time instant 50 min.…”