Cryogenics Safety Review of the ATLAS Experiment at CERN

The ATLAS detector at CERN to be installed at 90 m depth in a 50,000 m3 underground cavern is of unprecedented size and complexity. This is reflected in the helium and nitrogen cryogenic systems required respectively by the magnets (three large superconducting toroids and the central solenoid with 1.6 GJ stored energy) and by the argon calorimeters containing 82 m3 of liquid which can be drained into two 50 m3 dewars in case of emergency. Further coolants of 11 m3 of liquid helium and 15 m3 of liquid nitrogen are stored underground. The potential hazards of the large quantities of cryogens in underground areas require specific attention. Design, construction and quality assurance strictly follow applicable safety rules and the cryogenic process and controls are conceived to actively cope with a number of faults. In severe cases of accidental coolant loss (helium, nitrogen) or argon, detection systems produce alarms which result in the activation of emergency gas extraction. Reviews with international experts confirmed the good safety standard of the systems.