Task Force on Safety of Personnel in LHC underground areas following the sector 34 accident of 19-Sep-2008 Status report LPC 07/05/2009 B. Delille, S. Evrard, J. Inigo-Golfin, G. Lindell, G. Roy, L. Tavian, E. Thomas, R. Trant, C. Vollinger 1

Mandate  I Establish the sequence of facts related to safety of personnel, based on e.g. AL3 data and FB emergency intervention records.  II Analyse the LHC underground environmental conditions with respect to Safety of personnel and explain their development, in relation with original risk analyses (incl. tests) performed.  III Recommend preventive and corrective measures for the Safety of Personnel in the LHC underground 2

 Available data:  AL3 data (ODH, AFD);  FB intervention report;  He mass flow estimates;  Pt4: video surveillance A and B from access point  Manual actions on ventilation system & P3 outlet air measurements;  Sequence of facts from technical TF;  Eyewitnesses’reports from Pt4;  Geometry of tunnel [volume, length, …];  Position of equipment  Safety valves;  ODH sensors & AFD sensors;  Ventilation doors & inlets/outlets;  Available simulations:  EN-CV CFD simulation from March 2009  Wroclaw University of Technology, simulation from March 2009  Wroclaw University of Technology, ODH simulations from 1999  He spill and temperature simulations ( M. Vadon et. al.) from 2002  Available tests:  Wroclaw University of Technology, ODH propagation scaled tests from 1999  He spill test with QRL test cell inside a simulated tunnel from I SEQUENCE OF FACTS

4 ODH data From R. Nunes I SEQUENCE OF FACTS

Mass-flow discharge 5 Measurements on air outlet Pt3, 19-Sep-08 From L. Tavian & J. Inigo-Golfin Discharge temperature : ~40 – 60 K I SEQUENCE OF FACTS

Static Approach (I)– tunnel of volume V o filled only with air of pressure p o. (II) – tunnel after injecting some amount of helium under assumption that both gases do not mix together.  Adiabatic or isothermal compression of air 6 From M. Chorowski (WUT) II ANALYZE - EXPLAIN

Tunnel pressure increase 7 ~ :19:30 Door ~1.12 bar From L. Tavian II ANALYZE - EXPLAIN

The “scenario”  The accident results into He-release of ~2 tons within ~2 minutes;  Mass-flow of 15 to 26 kg/s for about 40 sec increases static pressure in “closed” ventilation area of sector 34 ;  At roughly 120 mbar static overpressure the sector door in UL44 gives in, thus creating a flushing of all sector 34;  Tunnel air and helium release to surface via UL44 and PM shaft to the SD surface bldg. 8 II ANALYZE - EXPLAIN

Preliminary result & conclusion Reoccurrence of an interconnect arc flash/MCI at any part of the cold machine cannot be excluded. and therefore the retained recommendations are  He release has to be confined to ventilation sector concerned in combination with a controlled release to the surface  No access to machine tunnel ventilation sector during machine conditions under which an interconnect arc flash/MCI might reoccur 9 III Recommendations

Recommendations (1/3) [Results of technical TF: Limit via machine protection systems the maximum possible amount of immediate He-release to 1100 kg (or 1500 kg for mid- arc)]  2-phase approach for machine powering (low- & high energy powering) – Threshold current value between phase I and phase II still has to be defined and agreed; – Technical means to control the different access phases still has to be defined and confirmed; – The TF expects an Engineering Spec. from the powering and access study team (see talk R.Schmidt, LMC ); – Areas possible to access in powering phase II: see later this talk. 10 III Recommendations

Recommendations (2/3)  Seal machine tunnel towards experimental caverns  Protect service caverns from ODH & overpressure from machine tunnel environment in case of MCI  Improve ventilation doors at the end of machine tunnel ventilation sector (pressure & tightness)  Controlled relief of the pressure from the ventilation area to the surface, i.e. mechanically improved ducts 11 III Recommendations

Recommendations (3/3)  Close beam pipe gate valves when no beam in the machine.  Empty the LHC from LHe when going into machine shutdown;  Heavy handling and transport restrictions for machine tunnel;  Equip machine tunnel sectors with sensors monitoring T, p & air speed [REs & LSSs]. 12 III Recommend

Preliminary compensatory measures for ‘09 shutdown: machine (1/2) Controlled release to surface from ventilation sector concerned via UL → PM-shaft → SD surface bldg.  UL doors “open”  No access to adjacent ventilation areas: see access matrix  SD bldg. with ODH/evacuation alarm and overpressure protected 13 III Recommend

14  Max local pressure if only 1 UL door ‘open’ per sector 3.3km  P = 90 mb PM shaft SD building  P = 20 mb III Recommendation Preliminary compensatory measures for ‘09 shutdown: machine (2/2) MCI: 40 kg/s at 200K Maximum local pressure expected 110 mb [final configuration with improved ventilation ducts: ~70 mbar]

Choice 1: UL doors open  Low overpressure (~20mb)  light sealing of Experimental caverns  No access to UL, US, restrictions in SD Choice 2: UL doors tights  High overpressure (~110mb)  heavy sealing + structure reinforcements  No access restrictions to Exp. facilities. All underground points have different topologies. Unique recommendation from TF but individual solutions only. 15 III Recommendations Preliminary compensatory measures for ‘09 shutdown: The impact for experiments (in brief)

Preliminary compensatory measures for ‘09 shutdown: experiments  Access to service cavern during phase II powering ONLY with implemented separation from machine tunnel  Access to experimental cavern during phase II powering ONLY with implemented separation from machine tunnel n.B.: Remember general condition of beam pipe gate valves being closed and protected against overpressure while NO beam 16 III Recommendations

Access matrix – DRAFT for 2009/10 17 III Recommendations  Sealing of experimental cavern is assumed to be completed  The matrix may change depending on the local implementation of the recommendation

Open Points Risk to personnel following “mechanical impact” to experiment beam tube and/or inner detectors from arc flash resulting in a loss of He containment into beam pipe. May similar scenario happen to ATLAS/CMS SC magnets? 18 III Recommendations

Proposal for other follow-up actions  Safety TF: elaborate detailed “matrix of access” to tunnel sectors/experiments/adjacent tunnels;  R. Schmidt’s team: Establish the threshold value for the current limit between the machine phases I & II;  EN/CV: carry out an implementation study for pressure release via ventilation ducts to the surface  EN/HE: implement re-enforced and “tight” ventilation doors  GS/SEM: implement SD bldg. protection  GS/ASE: install ODH/evac. Alarm in SD bldg’s  GS/ASE & BE/OP: Feasibility study for access interlocks other than RP during different machine phases.  TE/CRG: monitoring of T,p for future incident analyses (no online monitoring);  Working Group for structural integrity (initiated by S.Myers); 19 III Recommendations