The Sector 3-4 incident at the LHC: fault tree and corrective measures Ph. Lebrun Risk Analysis Review Committee CERN, 5 March 2009

Absence of soldering Resistance 200 nOhmBad contact with stabilizer No sensitive detection on bus bar Thermal runaway Meltdown, open circuitPower converter fast discharge Electrical arc Fault tree [1/3] Electro-thermal model Observed on magnet

Fault tree [2/3] Electrical arc Beam pipe perforation He vessel perforationSoot He discharge in insulation vacuum Contamination by sootInadequate sizing of relief devices (MCI) Pressurization of vacuum enclosures Mechanical damage to MLI Contamination by MLI ODH in tunnelBlast Trip AUG Loss of beam vacuum Break vent door

Fault tree [3/3] Pressurization of vacuum enclosures Pressure forces on vacuum barriers Plastic deformation of shellsBuckling of bellows Rupture of supports and ground anchors Displacement of magnets Mechanical damage to interconnects Secondary electrical arcs Damage to tunnel floor Used to estimate max pressure reached

Absence of soldering Resistance 200 nOhmBad contact with stabilizer No sensitive detection on bus bar Thermal runaway Meltdown, open circuitPower converter fast discharge Electrical arc Corrective measures [1/3] Measurement of joint resistance (calorimetry & electrical) Additional quench detection on bus bars

Absence of soldering Resistance 200 nOhmBad contact with stabilizer No sensitive detection on bus bar Thermal runaway Meltdown, open circuitPower converter fast discharge Electrical arc Corrective measures [1/3] Measurement of joint resistance (calorimetry & electrical) Additional quench detection on bus bars Mechanical clamping of joints?

Corrective measures [2/3] Electrical arc Beam pipe perforation He vessel perforationSoot He discharge in insulation vacuum Contamination by sootInadequate sizing of relief devices (MCI) Pressurization of vacuum enclosures Mechanical damage to MLI Contamination by MLI ODH in tunnelBlast Trip AUG Loss of beam vacuum Break vent door Revised MCI New relief devices Harden AUGHarden vent door

Corrective measures [2/3] Electrical arc Beam pipe perforation He vessel perforationSoot He discharge in insulation vacuum Contamination by sootInadequate sizing of relief devices (MCI) Pressurization of vacuum enclosures Mechanical damage to MLI Contamination by MLI ODH in tunnelBlast Trip AUG Loss of beam vacuum Break vent door Revised MCI New relief devices Harden AUGHarden vent door Trigger q-valves? Fire q-heaters?

Corrective measures [3/3] Pressurization of vacuum enclosures Pressure forces on vacuum barriers Plastic deformation of shellsBuckling of bellows Rupture of supports and ground anchors Displacement of magnets Mechanical damage to interconnects Secondary electrical arcs Damage to tunnel floor Reinforce ground anchors