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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

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MandateI 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

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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 2001

I SEQUENCE OF FACTS

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ODH data

From R. Nunes

I SEQUENCE OF FACTS

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Mass-flow discharge

14:30 14:55 15:13 16:10 16:45 17:55 % N2 49 39 44 41 41 43 % O2 12 9 10 10 10 11 % He 39 51 46 47 47 46 Measurements on air outlet Pt3, 19-Sep-08

From L. Tavian & J. Inigo-Golfin

Point 32

Point 2

Point 1

Point 4Point 5

Point 6

Point 7

Point 8

SECTEUR 3-4

SECTEUR 2-3

SECTEUR 1-2SECTEUR 8-1 SECTEUR 7-8

SECTEUR 6-7

SECTEUR 5-6

SECTEUR 4-5

Point 33

PGCN2

NEUTRINO

TI 8TI 2

PMI 2

CessyEchenevex

Crozet

St Genis Prevessin

Meyrin

Ferney

Versonnex

Gex

SPS

N

STCV- 97- C:\CM/ LHCST01.DS4

PAM4

D

M

D

M

D

M

D

M

M

M

M

M

M

M

M

M

TUNNEL NON ACCESSIBLE

45 000 / 45 000 m3/h

36 000 / 36 000 m3/h

36 000 / 36 000 m3/h

45 000 / 36 000 m3/h

36 000 / 45 000 m3/h

36 000 /36 000 m3/h

36 000 /36 000 m3/h

36 000 /36 000 m3/h

M

M

9 000 m3/h 9 000 m3/h

0

5

10

15

20

25

30

0 60 120 180 240 300

Dis

char

ged

mas

s-flo

w [k

g/s]

Time [s]

Sub-sector1Sub-sector2 + Line E + Line CSub-sector3Total

Discharge temperature : ~40 – 60 K

I SEQUENCE OF FACTS

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Static Approach(I) – tunnel of volume Vo

filled only with air of pressure po.

(II) – tunnel after injecting some amount of helium under assumption that both gases do not mix together.

Adiabatic or isothermal compression of air

From M. Chorowski (WUT)

II ANALYZE - EXPLAIN

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Tunnel pressure increase

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

0 500 1000 1500 2000 2500

Max

imum

pre

ssur

e [b

ar]

Mass of He [kg]

100 K adia100 K isoT200 K adia200 K isoT300 K adia300 K isoT

~ 800 kg @ 11:19:30

Door rupture @ 11:19:30@ ~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.

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II ANALYZE - EXPLAIN

Preliminary result & conclusionReoccurrence of an interconnect arc flash/MCI atany 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 11-03-09);– Areas possible to access in powering phase II: see later this talk.

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III Recommendations

Recommendations (2/3)Seal machine tunnel towards experimental

cavernsProtect 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

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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].

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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 matrixSD bldg. with ODH/evacuation alarm and

overpressure protected

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III Recommend

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Max local pressure if only 1 UL door ‘open’ per sector

3.3km DP = 90 mb

PM s

haft

PM s

haft

SD building

DP

= 20

mb

III RecommendationPreliminary 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.

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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 poweringONLY 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

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III Recommendations

Access matrix – DRAFT for 2009/10

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III Recommendations

Sealing of experimental cavern is assumed to be completedThe 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?

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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);

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III Recommendations