Conclusion of the He Spill Simulations in the LHC Tunnel

The LHC, currently under construction at CERN, will make use of superconducting magnets operating in super-fluid helium below 2 K provided via a separate cryogenic distribution line. An accidental spill of part of the helium inventory (approx. 12 tons per octant of 3.3-km length each) in the 3.8-m diameter underground tunnel is a potential risk to personnel i.e. lack of visibility, cold, lack of oxygen. Using a finite volume model of a 100-m long typical tunnel section, several scenarios with different leak rates and temperatures were simulated. Further parameters considered were ventilation rate, slope of the tunnel, helium leak temperature, etc. in order to point out the most critical factors influencing temperature and helium concentration distribution in the tunnel. Finally, this analysis allowed us to determine a maximum mass flow that can be released in the tunnel without putting personnel at risk.